Early Monday morning storm update

Quick update on the situation this morning...

Scattered showers and thunderstorms are forming and moving northeast across AR early this morning, with some crossing the Mississippi River and other forming pretty quickly over west TN at 4:45am. Severe limits have not been crossed by most of the storms, but they are moving into an area that has the ingredients for them to become severe. The most concerning severe weather parameters seem to be lining  up over much of southern west TN and extreme northern  Mississippi according to realtime analysis of the event from the Storm Prediction Center website.

While a squall line has not yet formed, according to Little Rock Doppler Radar, several clusters and mini-lines have formed over Arkansas.  As they move east, I expect some will merge and form some sort of larger line, particularly north of the metro region.  Any storms that can gather enough strength could become severe with damaging wind the primary threat and a few tornadoes the secondary threat.  A Tornado Watch remains in effect for west TN and northeast AR until 9am. The threat of severe weather will continue through rush hour until approximately 8am.  We remain under a Slight Risk of severe weather.

MemphisWeather.net will cover the storm throughout the duration of the event. Remember that roads will be wet and storms will be in the area during the morning commute. Slow down, use low-beam headlights and wipers, and maintain a safe distance.

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Update on severe weather expectations for tonight

Latest severe weather risk outlook for tonight from the NWS/Storm Prediction Center

It's amazing how similar tonight and last Thursday night's severe weather episodes seem to be, outside of the difference in timing of the event.

Thursday, I was expecting scattered severe storms to fire up in the mid to late afternoon and a squall line to race through in the late evening. The scattered storms never got going much, outside of one near Jackson, TN, while the squall line came through a couple of hours earlier than expected. Today, we are once again watching for scattered severe supercells to possibly form through the evening hours, followed by a potential squall line early Monday morning.  Both events saw the Mid-South in a moderate risk a day ahead of the event, though for tonight the Memphis metro is on the southern edge of the moderate risk versus in the middle of it thanks to a slightly more northerly track to the culprit low pressure system. It will be interesting to see exactly how this event plays out.

We'll be watching StormView Radar closely for isolated to scattered storms to fire up anytime through the evening and early overnight hours.  A little Weather 101... If these storms can "break the cap" and "become surface-based," we have a threat of tornadoes on our hands. If not, the threat is lower. This is what is called a "conditional" chance of severe weather - the severity of the storms is based on the conditions named above. The "cap" is like a lid on the atmosphere that keeps storms at bay. Without going into detail, if the lid, which is holding all of the energy under it, is released (or broken), then storms can literally explode upwards. The storms also need to become surface-based, which in essence means they get their energy from the heating at the surface of the earth. If a storm can't tap into the energy of the lowest levels of the atmosphere, it is what is referred to as an "elevated" storm. Typically, a storm must become surface-based to be tornadic.

So, the details on tonight's forecast... or at least my best educated guess. If storms can form and meet the above parameters, we could be looking at scattered supercellular thunderstorms beginning anytime and lasting through the early overnight hours. I put the chance of storms such as these at about 40%. If they form, you need to have your severe weather action plan in place. Later in the night, probably between 3-6am, a line or lines of storms are expected to move into the region from Arkansas and sweep across the metro area.  This line could be very similar to Thursday evening's line, posing a damaging wind threat, along with isolated tornadoes.  Any tornadoes that form tonight could be strong, as wind at the lower and mid levels of the atmosphere is strong enough to support them.

By morning rush hour, most activity will be moving east and scattered showers will remain as the cold front itself passes through. Lows tonight will be in the mid 60s, but expect wind to shift to the northwest and temperatures to fall into the 50s during the day. Calmer weather should persist for much of the rest of the work week.

When planning for severe weather, please visit the MWN Storm Center for the latest radar, severe weather watches and warnings, and severe weather safety tips. It's also an excellent idea to check your NOAA Weather Radios for fresh batteries and have them programmed to alarm in case of severe storms. Overnight severe weather is a great concern as many people could be unaware of what's going on outside until it's too late. MWN will also provide coverage of the severe weather threat as best as possible throughout the overnight hours via Facebook and Twitter and MWN's web products.

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Significant severe weather outbreak expected tonight

Sunday/Sunday night severe weather risk areas from the NWS/Storm Prediction Center

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MEMPHIS TN
527 AM CST SUN FEB 27 2011

...SIGNIFICANT SEVERE WEATHER OUTBREAK EXPECTED TONIGHT THROUGH
MONDAY MORNING ACROSS THE MID-SOUTH...

SEVERE WEATHER IS LIKELY TONIGHT INTO MONDAY MORNING ACROSS THE
MID-SOUTH INCLUDING THE POTENTIAL FOR WIDESPREAD DAMAGING WINDS AND
A FEW STRONG TORNADOES. THERE IS A MODERATE RISK OF SEVERE
THUNDERSTORMS ACROSS EAST ARKANSAS...THE MISSOURI BOOTHEEL...MOST
OF WEST TENNESSEE...AND A SMALL PART OF EXTREME NORTHWEST
MISSISSIPPI. THE MODERATE RISK AREA IS GENERALLY ALONG AND TO THE
NORTHWEST OF A LINE FROM WEST HELENA ARKANSAS TO HERNANDO
MISSISSIPPI TO HUNTINGDON TENNESSEE. THIS INCLUDES THE CITIES OF
MEMPHIS...JONESBORO...AND JACKSON. TO THE SOUTHEAST OF THIS AREA
INCLUDING MUCH OF NORTH MISSISSIPPI...A SLIGHT RISK OF SEVERE
THUNDERSTORMS EXIST. THE SLIGHT RISK AREA INCLUDES TUPELO.

A POWERFUL LOW PRESSURE SYSTEM AND AN ASSOCIATED COLD FRONT WILL
MOVE INTO THE REGION TONIGHT. WITH INCREASING INSTABILITY AND
STRENGTHENING WINDS IN THE UPPER ATMOSPHERE ACROSS THE
MIDSOUTH...SEVERE THUNDERSTORMS WILL DEVELOP AHEAD OF THIS SYSTEM
BEGINNING THIS EVENING. THE INITIAL THREAT OF SEVERE WEATHER WILL
COME FROM SCATTERED THUNDERSTORMS THAT MOVE INTO EAST ARKANSAS
AND THE MISSOURI BOOTHEEL AFTER 7 PM...AND INTO WEST TENNESSEE
AFTER 10 PM. A FEW OF THESE THUNDERSTORMS MAY BECOME SEVERE WITH
THE POTENTIAL FOR A FEW STRONG TORNADOES. A SQUALL LINE IS THEN
FORECAST TO MOVE INTO EAST ARKANSAS AFTER 10 PM...CROSSING THE
MISSISSIPPI RIVER AFTER 1 AM MONDAY. THIS SQUALL LINE WILL HAVE
THE POTENTIAL FOR WIDESPREAD DAMAGING WINDS ALONG WITH A FEW
EMBEDDED TORNADOES. A FEW STRONG TORNADOES ARE ALSO POSSIBLE WITH
THE SQUALL LINE OR ANY THUNDERSTORMS THAT MAY DEVELOP JUST AHEAD
OF THE LINE. ANY OF THE SEVERE THUNDERSTORMS TONIGHT AND MONDAY
MORNING WILL ALSO HAVE THE POTENTIAL TO PRODUCE LARGE HAIL. HEAVY
DOWNPOURS MAY ALSO CAUSE LOCALIZED FLASH FLOODING. THE SEVERE
WEATHER THREAT WILL CONTINUE ACROSS PORTIONS OF WEST TENNESSEE AND
NORTH MISSISSIPPI THROUGH MONDAY MORNING...CROSSING THE TENNESSEE
RIVER BY NOON.

NOW IS THE TIME TO PREPARE FOR THIS SEVERE WEATHER EVENT. SINCE
THIS SEVERE WEATHER EVENT WILL CONTINUE THROUGHOUT THE OVERNIGHT
HOURS TONIGHT AFTER MANY PEOPLE HAVE GONE TO SLEEP...IT IS
ESPECIALLY IMPORTANT THAT YOU CHECK THE BATTERIES IN YOUR NOAA
WEATHER RADIO... MAKE SURE THE RADIO IS WORKING PROPERLY...AND SET
THE RADIO TO ALARM FOR WHEN SEVERE WEATHER WATCHES AND WARNINGS ARE
ISSUED. ALSO...KEEP IN MIND THAT MOBILE HOMES ARE ESPECIALLY
VULNERABLE TO THE DANGERS OF HIGH WINDS. PLAN NOW TO KNOW WHERE
YOU WOULD SEEK A SAFE SHELTER IF SEVERE WEATHER OCCURS.

PLEASE KEEP IN TOUCH WITH THIS DEVELOPING WEATHER SITUATION THROUGH
NOAA WEATHER RADIO...COMMERCIAL RADIO...OR TELEVISION.


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Damage surveyed in Crittenden and Shelby Counties - up to 95 mph wind noted

The following survey notes were taken by the National Weather Service following a damage survey from the storms that occurred Thursday evening, February 24, 2011.

...PRELIMINARY SUMMARY FROM CRITTENDEN AND SHELBY COUNTIES...

* COUNTIES: CRITTENDEN IN ARKANSAS...SHELBY IN TENNESSEE
* LOCATIONS: CRAWFORDSVILLE...MARION...MILLINGTON...AND BARTLETT
* TIME OF EVENT: FEB 24 2011 BETWEEN 6:30 PM AND 7:05 PM
* ESTIMATED PEAK WIND: 85-95 MPH
* INJURIES: NONE

* SUMMARY OF DAMAGES: DAMAGING STRAIGHT LINE WINDS MOVED THROUGH
EASTERN CRITTENDEN AND NORTHERN SHELBY COUNTY. THE PATH OF
DAMAGE BEGAN NEAR THE TOWN OF CRAWFORDSVILLE. SEVERAL TREES WERE
DOWN OR SUFFERED LIMB DAMAGE. SHINGLES OR METAL ROOFING WAS
RIPPED OFF SEVERAL STRUCTURES. SEVERAL PICKUP TRUCKS AND LARGE
TRACTORS FOR FARMING HAD BROKEN WINDOWS. WINDS IN THIS AREA WERE
ESTIMATED AT AROUND 80 TO 85 MPH. WIND DAMAGE WAS ALSO FOUND AT
THE DELTA ACRES SUBDIVISION LOCATED 5 MILES NORTH OF MARION
ALONG HIGHWAY 77. SEVERAL TREES AND FENCES WERE BROKEN OR DOWN
IN THIS AREA. SIDING AND SHINGLES WERE OFF OF ALMOST ALL THE
HOUSES IN THIS SUBDIVISION. WINDS IN THIS LOCATION WERE
ESTIMATED AT 70 TO 80 MPH. THE STORM CONTINUED TO MOVE EAST AND
CROSSED THE MISSISSIPPI RIVER. THE DAMAGE PATH CONTINUED NEAR
MEEMAN-SHELBY FOREST STATE PARK. POWERLINES WERE DOWN...TREES
AND A METAL SHED WERE ALSO DAMAGED. A SMALL PLANE WAS FLIPPED
OVER AT THE CHARLES W BAKER AIRPORT AND A NEARBY FIRE DEPARTMENT
SUSTAINED SOME ROOF DAMAGE. WIND SPEEDS IN THIS AREA WERE
ESTIMATED AT 70 MPH. THE STORM ENTERED MILLINGTON AT AROUND 6:55
PM...PRODUCING TREE AND SHINGLE DAMAGE ACROSS THE CITY. TREES
AND POWERLINES WERE SNAPPED ALONG NAVY ROAD AND SINGLETON ROAD
ON THE NAVAL BASE. WIND SPEEDS IN MILLINGTON WERE ESTIMATED AT
85 TO 95 MPH. SHINGLE DAMAGE WAS ALSO NOTED ACROSS BARTLETT.
WIND SPEEDS ARE ESTIMATED AT 60 TO 70 MPH. NO TORNADO DAMAGE WAS
NOTED IN THE DAMAGE ALONG THIS STORM PATH.

The following damage pictures were taken by MemphisWeather.net near the intersection of Kirby-Whitten and Old Brownsville Roads in north Bartlett.  Click each for larger images.

Metal shed lifted from it's foundation and flipped through a fence

Trampoline blown approximately 200 feet across a vacant lot until it reached the fence

A/C unit tilted on it's side at the house where the trampoline above originated

Another potential severe weather event and how it compares to Thursday's severe weather

As things have started to settle down from Thursday night's severe weather episode and most folks power is now restored, I thought it necessary to at least start talking about the next potential severe weather event to impact the Mid-South.

We experienced a very cool and cloudy day today with high temperatures about 30 degrees colder than Thursday, when the Mid-South was in a warm sector ahead of the line of storms that blasted through Thursday evening. Temperatures will drop only a little overnight, reaching the mid 30s as clouds hang tight. By Saturday afternoon, a warm front will again move through, scouring out the clouds and sending temperatures back into the lower 60s. Sunday is "setup" day once again as the Mid-South remains firmly entrenched in the warm sector ahead of yet another strong weather system. We could see scattered showers and perhaps a few thunderstorms during the day as high temperatures will be similar to Thursday - in the lower to mid 70s - with fairly muggy and breezy conditions.

The potential severe weather event will occur late Sunday night or early Monday morning. A couple of differences from the Thursday evening system:

1) The low pressure center that is forcing a strong cold front through the region will be much further north this time - moving from Kansas into the southern Great Lakes rather than across northern Arkansas into the Ohio Valley.
2) The timing of the storms will be early morning versus early evening, which could play a key role in available instability, as it will be during the "coolest" part of the day versus the warmest, and thus potentially limiting one of the factors necessary.

On the other hand, even given the typically less-favorable low pressure track well to our north, jet stream dynamics at all levels will be favorable for the development of high winds and isolated tornadoes, very similar to the Thursday night event. While any tornado activity would again be more likely in supercells ahead of a squall line, these storms would have to form during the overnight hours Sunday night rather than during peak heating. While this is certainly not uncommon, it seems less likely at this time of year and given the recent history of a lack of pre-squall line supercells on Thursday afternoon.

My expectation is that we will see scattered showers and isolated non-severe thunderstorms on Sunday, followed by a somewhat "quiet" period much of Sunday night, then a fast-moving squall line containing high wind and an isolated tornado threat sometime around dawn on Monday morning (a very similar scenario to Thursday evening).  It should be noted that one of the short-range models (the NAM) is beginning to push the timing of the line into the mid-morning hours Monday. Given the potential for a fast-moving squall line and the models typically underplaying forward propagation in this type of system, I believe it could be quicker than that. Stay tuned and begin reviewing those severe weather safety tips once again!

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SKYWARN Storm Spotters - the eyes and ears of the NWS

SEVERE WEATHER AWARENESS WEEK CONCLUDES WITH A LOOK AT SKYWARN.

SEVERE WEATHER CAN STRIKE DURING ANY MONTH OF THE YEAR AT ANY TIME OF THE DAY OR NIGHT. WHEN SEVERE THUNDERSTORMS THREATEN... THE NATIONAL WEATHER SERVICE CALLS SKYWARN VOLUNTEERS INTO ACTION.

SKYWARN VOLUNTEERS ARE THE EYES AND EARS OF THE NATIONAL WEATHER SERVICE... PROVIDING INSTANT REPORTS OF SEVERE WEATHER... INCLUDING HAIL... HIGH WINDS... AND DANGEROUS CLOUD FORMATIONS.

SKYWARN SPOTTERS KEEP A CLOSE EYE ON THE SKY ANYTIME SEVERE THUNDERSTORMS APPROACH. MANY COMMUNITIES DEPLOY SPOTTERS AROUND THE EDGE OF THE CITY AND USE THEIR EARLY REPORTS OF IMPENDING HAZARDOUS WEATHER TO WARN THE COMMUNITY. SOME SPOTTERS RELAY REPORTS FROM THEIR HOME OR BUSINESS WHILE OTHER MORE ADVENTUROUS VOLUNTEERS BRAVE THE ELEMENTS AND TRY TO GET AS CLOSE TO THE STORM AS POSSIBLE.

WHO ARE THESE SKYWARN VOLUNTEERS? A LARGE NUMBER OF SKYWARN STORM SPOTTERS IN THE MID-SOUTH ARE AMATEUR RADIO OPERATORS... OR HAMS. THESE PUBLIC-SERVICE MINDED INDIVIDUALS MAKE IDEAL STORM SPOTTERS... SINCE THEY HAVE THE ABILITY TO COMMUNICATE THEIR REPORTS. THEY ARE WILLING TO BE TRAINED AND THEY HAVE A REAL INTEREST IN HELPING THE NATIONAL WEATHER SERVICE AND THEIR LOCAL COMMUNITIES PREPARE FOR SEVERE WEATHER. AMATEUR RADIO OPERATORS ARE ON CALL 24 HOURS A DAY... 365 DAYS A YEAR... EVEN THOUGH THEY RECEIVE NO COMPENSATION OF ANY KIND FOR THEIR HARD WORK.

MANY OTHER GROUPS PARTICIPATE IN THE SKYWARN PROGRAM... INCLUDING LAW ENFORCEMENT AGENCIES... FIRE DEPARTMENTS... UTILITY COMPANIES... RESCUE SQUADS... AND THE NEWS MEDIA. IN SOME AREAS... INDIVIDUAL CITIZENS ARE TRAINED AS SPOTTERS AND ARE ASKED TO RELAY THEIR REPORTS TO THE NATIONAL WEATHER SERVICE. SPOTTERS ARE A VITAL LINK IN THE WARNING PROCESS. IT IS IMPORTANT TO HAVE AS MANY TRAINED SPOTTERS IN EACH COUNTY AS POSSIBLE.

NOTE: The National Weather Service will be conducting basic SKYWARN spotter training on Saturday, February 26, 2011 at the Agricenter in Cordova at 10:00am.  The class is free with no reservations required and will last a little over two hours. Teens are welcome to attend with their parents. For more information, contact the National Weather Service at (901) 544-0401.

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NOAA Weather Radio and the Emergency Alert System

...NOAA WEATHER RADIO AND THE EMERGENCY ALERT SYSTEM...

SEVERE WEATHER AWARENESS WEEK CONTINUES. TODAY WE WILL FOCUS ON WEATHER RADIO AND THE EMERGENCY ALERT SYSTEM.

WEATHER RADIO IS THE VOICE OF THE NATIONAL WEATHER SERVICE. IT PROVIDES CONTINUOUS WEATHER INFORMATION 24 HOURS A DAY... EVERY DAY OF THE YEAR. THE NATIONWIDE NETWORK OF WEATHER RADIO STATIONS PROVIDES THE PUBLIC WITH THE FASTEST MOST RELIABLE SOURCE OF UP-TO-DATE WEATHER INFORMATION DIRECTLY FROM THE NATIONAL WEATHER SERVICE.

YOU NEED A SPECIAL RADIO TO RECEIVE WEATHER RADIO BROADCASTS... A RADIO THAT IS CAPABLE OF RECEIVING SIGNALS IN THE VERY HIGH FREQUENCY PUBLIC SERVICE BAND.

BROADCASTS MAY VARY... BUT GENERALLY INCLUDE AREA FORECASTS... PRESENT WEATHER CONDITIONS... SHORT-TERM FORECASTS... CLIMATIC DATA... RIVER AND LAKE STAGE FORECASTS... AND OTHER SPECIALIZED INFORMATION. THE BROADCASTS ARE UPDATED CONTINUOUSLY.

WEATHER RADIO IS USEFUL ANYTIME... BUT IT IS MOST IMPORTANT WHEN SEVERE WEATHER THREATENS. DURING PERIODS OF SEVERE WEATHER... ROUTINE PROGRAMMING IS INTERRUPTED... AND THE FOCUS SHIFTED TO THE LOCAL SEVERE WEATHER THREAT. IN AN EMERGENCY... A WARNING ALARM TONE IS BROADCAST THAT ACTIVATES SPECIALLY DESIGNED RECEIVERS TO TURN ON AUTOMATICALLY... OR TO PRODUCE A VISUAL OR AUDIBLE ALARM.

A PRIMARY SOURCE OF WEATHER INFORMATION IS THE EMERGENCY ALERT SYSTEM. E A S IS A SYSTEM OF COMMUNICATIONS LINKS THAT UTILIZE DATA IN A DIGITAL FORM. IT IS A RELIABLE MEANS OF LINKING THE NATIONAL WEATHER SERVICE... EMERGENCY MANAGEMENT AGENCIES... AND THE RADIO AND TELEVISION BROADCAST MEDIA TOGETHER. E A S HELPS PARTICIPATING RADIO AND TELEVISION STATIONS RECEIVE AND RELAY WEATHER WARNINGS... AND OTHER EMERGENCY INFORMATION IN A TIMELY MANNER.

FOR MORE INFORMATION ON WEATHER RADIO... CONTACT THE NATIONAL WEATHER SERVICE OFFICE IN MEMPHIS TENNESSEE.

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Thursday mid-day update on today's severe weather event

Severe weather risk for today, courtesy NWS-Storm Prediction Center

Tornado chances for today. Hatched area indicates 10%+ chance of EF2 or greater.

As of 12:00pm, environmental conditions are evolving about as expected. The warm front is moving north through the Memphis metro, bringing the unstable, warm, and muggy airmass into the region. North of the front, temperatures are in the 50s, while south of the front they are at or above 70 degrees already. Some breaks are observed in the clouds to the south of the front, which will allow high temperatures to reach the mid 70s with partial sun. A few spots south of the metro area could see highs in the upper 70s to near 80 with enough sun. With temps in the 70s and dewpoints in the 60s, the airmass will be unstable enough to support severe thunderstorms. The Storm Prediction Center has maintained the Moderate Risk of severe weather for the entire region and placed us in a 15% likelihood of a tornado within 25 miles of any point (see maps above).

So, by mid-afternoon (after 3pm), expect scattered storms to begin forming and quickly become strong to severe with large hail, damaging wind, and isolated tornadoes possible. These scattered supercell thunderstorms will continue around the region through evening before a pre-frontal trough arrives during the late evening hours (between 8-11pm). The trough will bring with it more organized line segments or perhaps a full-blown squall line of thunderstorms, which are expected to be severe. Tornadoes are once again a concern, as well as straight-line wind, as wind at 3-5,000 feet will be blowing at 60-75 mph. The cold front will arrive in the 11pm-1am time frame and could bring a few more thunderstorms, though I don't expect them to be "as severe" as the earlier storms.

MWN is now operating in "Severe Weather Mode."  The MWN Storm Center has all the information you need as far as safety tips, watches/warnings, radar, and more. You should also keep an eye on StormView Radar as storms begin forming this afternoon.  It is also advisable, especially if you follow MWN on social media channels, to read our policy on severe weather coverage (PDF).  We'll bring your the latest information throughout today's event.

MWN meteorologist Erik Proseus was interviewed by 600WREC's Tonya J. Powers this morning regarding severe weather safety. To listen to the interview, click here (MP3).

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Flooding and Flash Flood Awareness Day

Flooding from a stream that overflowed its banks on May 1, 2010

..FLOOD AND FLASH FLOOD AWARENESS DAY...

SEVERE WEATHER AWARENESS WEEK CONTINUES TODAY WITH A LOOK AT FLOOD AND FLASH FLOOD SAFETY.

FLOODS AND FLASH FLOODS OCCUR EVERY YEAR IN THE MID-SOUTH. RIVER FLOODING OCCURS SEASONALLY WHEN WINTER OR SPRING RAINS OR TORRENTIAL RAINS ASSOCIATED WITH TROPICAL STORMS FILL RIVER BASINS WITH TOO MUCH WATER TOO QUICKLY. FLASH FLOODS OCCUR SUDDENLY... USUALLY OCCURRING WITHIN HOURS OF EXCESSIVE LOCALIZED RAINFALL. THESE FLASH FLOODS CAN BECOME RAGING TORRENTS WHICH RIP THROUGH RIVER BEDS... URBAN STREETS... OR VALLEYS SWEEPING EVERYTHING BEFORE THEM.

WHEN A FLASH FLOOD WARNING IS ISSUED FOR YOUR COUNTY... OR THE MOMENT YOU FIRST REALIZE THAT A FLASH FLOOD IS IMMINENT...   ACT QUICKLY TO SAVE YOURSELF. YOU MAY ONLY HAVE SECONDS.

A FLOOD WATCH MEANS IT IS POSSIBLE THAT HEAVY RAINS WILL CAUSE FLOODING IN THE SPECIFIED AREA. STAY ALERT TO THE WEATHER... AND THINK ABOUT WHAT YOU WOULD DO IF WATER BEGINS TO RISE OR IF YOU RECEIVE A WARNING. WATCH FOR DEVELOPMENT.

HERE ARE SOME FLASH FLOOD SAFETY RULES:

GET OUT OF AREAS SUBJECT TO FLOODING. THIS INCLUDES DIPS... LOW SPOTS... VALLEYS... STREAM BANKS... AND FLOOD PLAINS.

AVOID ALREADY FLOODED AND HIGH VELOCITY FLOW AREAS. DO NOT ATTEMPT TO CROSS A FLOWING STREAM ON FOOT WHERE WATER IS ABOVE YOUR ANKLES.

IF DRIVING... KNOW THE DEPTH OF WATER IN A DIP BEFORE CROSSING. THE ROAD BED MAY NOT BE INTACT UNDER THE WATER. DON'T DRIVE INTO A POOL OF WATER OR WHERE WATER IS FLOWING. WATER UP TO THE BUMPER WILL LIKELY STALL A CAR.

IF THE VEHICLE STALLS... ABANDON IT IMMEDIATELY AND SEEK HIGHER GROUND. RAPIDLY RISING WATER MAY ENGULF THE VEHICLE AND ITS OCCUPANTS AND SWEEP THEM AWAY.

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE FLOOD DANGERS. HEAVY RAIN EVENTS FREQUENTLY OCCUR AT NIGHT!

DO NOT CAMP OR PARK YOUR VEHICLE ALONG STREAMS OR DRAINAGE AREAS PARTICULARLY DURING THREATENING CONDITIONS.

SEVERE WEATHER AWARENESS WEEK CONTINUES TOMORROW WITH A LOOK AT NOAA WEATHER RADIO AND THE EMERGENCY ALERT SYSTEM.

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Severe weather outlook for Thursday

The severe weather threat for the Mid-South continues for Thursday as models are merging towards an outcome that seems plausible.  One of the questions posed in recent MWN blog posts has been with regards to the placement of the low pressure system and warm front. It now appears that the warm front will move through the metro area completely, stalling to our north and placing much of the region in the "warm sector."  This is an area where Gulf moisture will flow freely into the region and atmospheric dynamics will be maximized ahead of the approaching low.  The low pressure center itself will pass by to our north, likely moving across northern AR and then into western KY.  Again, we'll be in a favorable quadrant of the low for severe weather. The only real remaining question is instability, which will go up if we get any sunshine tomorrow and be somewhat minimized if we get rain showers during the day.

For these reasons, the Storm Prediction Center has issued a somewhat rare "Moderate Risk" area that encompasses the tri-state for tomorrow.  According to the NWS, only about 10 times a year are moderate risk areas issued for Day 2.  The risk area is shown in the map below.  The second map shows the probability of severe weather within 25 miles of any one point, with the hatched area (over west TN, N MS, and AR) indicating a 10% chance or greater of "significant severe" weather within 25 miles of any point.  In other words, it appears our chance of seeing severe weather in the metro is about 50/50 (which is pretty high).

Thunderstorms are possible overnight tonight and early tomorrow as the warm front moves through the region from south to north, though these storms will stay below severe limits. A lull in the action is expected tomorrow morning and early afternoon before storms begin to fire to our west by mid-afternoon. I expect the greatest threat of severe weather, including tornadoes, to be between 5-10pm in the immediate area, earlier in east AR and later to our east.  Very heavy rain, damaging straight-line wind, large hail, and frequent lightning are all possible to probable as well.

To review severe weather safety rules, visit previous MWN blog articles on Severe Thunderstorms, Lightning, and Tornadoes. If you haven't already, form a severe weather plan with your family (including any children living at home) and share it with them.

MWN will have you covered during this potential severe weather event through all of our various means of communication, including the website, blog, Facebook, and Twitter.

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Special Weather Statement concerning Thursday's severe weather potential

Severe weather risk for Thursday from the Storm Prediction Center

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MEMPHIS TN
257 AM CST WED FEB 23 2011

...STRONG STORM SYSTEM TO AFFECT THE MID-SOUTH LATE TONIGHT AND THURSDAY...

AN INTENSIFYING STORM WILL TRACK FROM THE SOUTHERN PLAINS INTO THE OHIO VALLEY BEGINNING LATE TONIGHT THROUGH EARLY FRIDAY MORNING... BRINGING A LIKELY THREAT OF SEVERE WEATHER AND POTENTIAL FLASH FLOODING TO THE MID-SOUTH. THUNDERSTORMS ARE FORECASTED TO DEVELOP TONIGHT ALONG AND AHEAD OF A WARM FRONT THAT WILL SURGE NORTH THROUGHOUT THE DAY ON THURSDAY... BECOMING STATIONARY ACROSS THE NORTHERN MID-SOUTH COUNTIES BY THURSDAY AFTERNOON. AT THE SAMETIME WIND FIELDS WILL BE INCREASING THROUGHOUT THE DAY AS WELL AS INSTABILITY. THIS WILL SET THE STAGE FOR STORMS TO BEGIN ROTATING... WITH THE GREATEST THREAT OF SEVERE WEATHER EXPECTED LATE THURSDAY AFTERNOON AND EVENING AS A COLD FRONT ADVANCES EAST OVER THE AREA. TORNADOES... LARGE HAIL... DAMAGING WINDS AND A CONTINUED THREAT FOR FLASH FLOODING IS LIKELY DURING THIS PERIOD.

THIS WILL BE THE FIRST SEVERE WEATHER EVENT OF THE YEAR AND RESIDENTS ACROSS THE MID-SOUTH ARE HIGHLY ENCOURAGED TO REVIEW SEVERE WEATHER SAFETY RULES NOW IN PREPARATION FOR THIS STORM EVENT. STAY TUNED TO THE LATEST INFORMATION CONCERNING THIS EXPECTED SEVERE WEATHER OUTBREAK.

Tornado Awareness Day

...TORNADO AWARENESS DAY...

YOUR SAFETY DEPENDS ON BEING CONSTANTLY ALERT TO THE POSSIBILITY OF TORNADOES FROM THE THUNDERSTORMS THAT APPROACH YOU. THIS IS ESPECIALLY TRUE DURING TORNADO WATCHES. A CAREFUL LOOKOUT SHOULD BE KEPT DURING ANY PERIOD OF SEVERE WEATHER ACTIVITY. PLAN IN ADVANCE WHERE YOU WILL GO AND WHAT YOU WILL DO IF A TORNADO THREATENS YOU.

REMEMBER... A TORNADO WATCH MEANS THAT TORNADO DEVELOPMENT IS POSSIBLE... SO WATCH THE SKY FOR DEVELOPING THUNDERSTORMS AND ALL THE HAZARDS THEY BRING. STAY TUNED TO WEATHER RADIO... COMMERCIAL RADIO OR TELEVISION FOR WEATHER STATEMENTS OR WARNINGS.

A TORNADO WARNING... USUALLY ISSUED FOR 1 OR 2 COUNTIES AT A TIME... MEANS THAT A TORNADO HAS BEEN SIGHTED... OR INDICATED BY WEATHER RADAR. PERSONS IN THE PATH OF THE STORM NEED TO IMMEDIATELY FIND SHELTER... PREFERABLY IN A STURDY BUILDING... BELOW GROUND IF POSSIBLE.

HERE ARE SOME TORNADO SAFETY RULES.

IN HOMES OR SMALL BUILDINGS... GO TO THE BASEMENT OR STORM SHELTER OR TO AN INTERIOR ROOM... SUCH AS A CLOSET OR BATHROOM... ON THE LOWEST LEVEL. GET UNDER SOMETHING STURDY SUCH AS A HEAVY TABLE OR A BED.

IN MOBILE HOMES AND VEHICLES... ABANDON THEM AND GO TO A STORM SHELTER OR STURDY STRUCTURE. IF THERE IS NO SUCH STRUCTURE NEARBY... LIE FLAT IN A DITCH RAVINE... GULLY... CULVERT... OR A LOW SPOT WITH YOUR ARMS AND HANDS SHIELDING YOUR HEAD.

IN LARGE BUILDINGS SUCH AS SCHOOLS... FACTORIES... HOSPITALS... NURSING HOMES... AND SHOPPING CENTERS... GO TO THE PREDESIGNATED SHELTER AREA. INTERIOR HALLWAYS ON THE LOWEST FLOOR ARE USUALLY BEST. STAY AWAY FROM ROOMS THAT ARE LARGE IN AREA BECAUSE THEY HAVE WEAKLY SUPPORTED ROOFS.

AT ALL TIMES... STAY AWAY FROM WINDOWS.

Photo of Murfreesboro, TN tornado taken by Titus Bartos, TitusBartos.com/PhotoBlog/


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Chance of severe weather remains in place Thursday

Possible setup for severe thunderstorms on Thursday, courtesy NWS-Memphis

According to today's computer model output, the severe weather threat remains intact for what could be the first severe weather event of 2011 across much of the Mid-South. There are still questions that linger, including the eventual track of the surface low pressure system that will move over the region and the amount of instability in the atmosphere, as well as the exact timing of the cold front. All of these factors affect the degree of severe weather, as well as the timing.

The NAM and European models have a slightly faster solution and move the surface low across northeast Arkansas into western Kentucky during the evening - a track favorable for severe weather as the entire area would get into what is called the "warm sector" of the storm, where warm moist Gulf air can flow unabated into region. The GFS model takes the low a little farther south, almost directly over Memphis, and is slower by about 6 hours. It also is the wettest solution, though the severe weather threat would be lower due to the warm sector remaining to our south.  The warm sector is the most favorable region for severe thunderstorms in most cases.  At this time, the favored model solution is the NAM/Euro, which is depicted in the graphicast provided by the NWS above.

The one thing I do expect is a lot of rain, with the possibility of flash flooding.  I would expect anywhere from 1-3" of rain depending on the ultimate placement of the fronts and low pressure track. Thunderstorms will first appear overnight Wednesday night (though these will likely be below severe limits with an outside chance of small hail) followed by a possible lull in the action during the morning hours Thursday. As the low and cold front approach, the "main event" will occur between Thursday mid-afternoon and midnight Thursday night.

Expect further blog updates as forecast confidence increases. Facebook and Twitter will be the best sources for real-time information during the event itself.

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Lightning Awareness Day

SEVERE WEATHER AWARENESS WEEK CONTINUES TODAY WITH A LOOK AT LIGHTNING SAFETY.  HERE ARE SOME LIGHTNING SAFETY RULES.

ANY LIGHTNING SAFETY PLAN SHOULD INCORPORATE THE 30/30 RULE. THE 30/30 RULE STATES PEOPLE SHOULD SEEK SHELTER IF THE FLASH TO BANG DELAY (LENGTH OF TIME IN SECONDS BETWEEN A LIGHTNING FLASH AND ITS SUBSEQUENT THUNDER) IS 30 SECONDS OR LESS AND THAT THEY REMAIN UNDER COVER UNTIL 30 MINUTES AFTER THE FINAL CLAP OF THUNDER.

MOVE INSIDE A WELL CONSTRUCTED HOUSE... A LARGE BUILDING... OR AN ALL METAL VEHICLE. STAY AWAY FROM ELECTRICAL APPLIANCES AND DO NOT USE THE TELEPHONE.

IF YOU ARE IN A BOAT... GET OFF THE WATER AND INTO A SUBSTANTIAL BUILDING... OR AT LEAST INTO AN ENCLOSED AND ALL-METAL VEHICLE WITH THE WINDOWS UP. IF YOU'RE CAUGHT IN AN OPEN METAL BOAT... LIE DOWN IN THE BOAT WITH CUSHIONS BETWEEN YOU AND THE METAL SIDES AND BOTTOM.

IF YOU ARE CAUGHT OUTDOORS... GET DOWN TO AVOID BEING THE HIGHEST POINT FOR A LIGHTNING DISCHARGE. IF YOU'RE CAUGHT IN A FLAT OPEN FIELD OR IF YOU FEEL YOUR HAIR STANDING ON END... CROUCH DOWN AND COVER YOUR HEAD WITH YOUR HANDS. THAT WAY... ONLY YOUR FEET WILL TOUCH THE GROUND.

MOVE AWAY FROM MOTORCYCLES... SCOOTERS... GOLF CARTS... BICYCLES... TRACTORS... AND OTHER METAL FARM EQUIPMENT. AVOID WIRE FENCES... CLOTHES LINES... METAL PIPES... DRAINS... RAILROAD TRACKS... AND OTHER METALLIC OBJECTS.

AVOID LONE TREES AND THE TALLEST TREES. IF CAUGHT IN THE WOODS... PICK A SMALL GROVE OF TREES AS YOUR SHELTER... AND STAND AT LEAST 5 FEET FROM THE TRUNK OF THE NEAREST TREE TO AVOID FLYING BARK IF THE TREE IS STRUCK.

AVOID STANDING IN A SMALL ISOLATED SHED OR OTHER SMALL UNGROUNDED STRUCTURE IN OTHER AREAS.

IF IN A GROUP OF PEOPLE IN AN OPEN AREA... SPREAD OUT BEFORE YOU KNEEL DOWN.

ON WEDNESDAY... A TORNADO DRILL WILL BE CONDUCTED BETWEEN 9 AND 10AM IN TENNESSEE... ARKANSAS... AND MISSISSIPPI.

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Actual severe weather during Severe Weather Awareness Week?

Area being monitored for the potential for severe weather on Thursday

The timing would be impeccable, but the chances are increasing that some of the safety tips we pass on this week regarding severe weather might actually be needed before the week is out.

After today's cold front, the atmosphere will reset for the next strong cold front/low pressure system that will move through the region on Thursday. The computer models are working out their differences, but some parameters required for severe weather look like they will be in place.  The track of the low pressure system could be one of the last ingredients to come into place, and it may or may not be ideal. The other uncertainty is in the amount of energy available (atmospheric lift) as the system moves through. Given a favorable track for the low, that uncertainty could be overcome. The one thing that does look favorable, though also not ideal, is strong winds and wind shear.  The upper level jet stream will be just to our north, while the low and mid level jet streams will be over the region.

We'll continue to monitor this developing scenario and bring you the latest via the MWN Storm Center, MWN Forecast, this blog, Facebook and Twitter. In the meantime, pay attention to the severe weather safety tips that you hear throughout the week. This storm system will be capable of damaging straight line wind, lightning, hail, flooding, and possibly even tornadoes.

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Severe Thunderstorm Awareness Day

...SEVERE THUNDERSTORM AWARENESS DAY...

SEVERE WEATHER AWARENESS WEEK IN THE MID-SOUTH BEGINS WITH A LOOK AT SEVERE THUNDERSTORMS.

THERE ARE APPROXIMATELY TWO THOUSAND THUNDERSTORMS IN PROGRESS AROUND THE WORLD AT ANY GIVEN TIME. MOST OF THESE STORMS ARE BENEFICIAL AND BRING NEEDED RAIN. ONLY A SMALL FRACTION... LESS THAN ONE PERCENT... ARE CLASSIFIED AS SEVERE. SEVERE THUNDERSTORMS ARE THOSE THUNDERSTORMS THAT PRODUCE HAIL ONE INCH IN DIAMETER OR LARGER AND/OR STRONG WIND GUSTS OF 58 MPH OR GREATER. HAIL THAT IS ONE INCH IN DIAMETER IS ABOUT THE SIZE OF A QUARTER.

A SMALL FRACTION OF SEVERE THUNDERSTORMS PRODUCE TORNADOES. ALL THUNDERSTORMS ARE CAPABLE OF PRODUCING DEADLY LIGHTNING. THE HEAVY RAIN OR LIGHTNING ACTIVITY IN A THUNDERSTORM DO NOT HAVE ANYTHING TO DO WITH A THUNDERSTORM BEING CLASSIFIED AS SEVERE.

SOME OF THE SEVERE THUNDERSTORMS SAFETY RULES ARE AS FOLLOWS.

FIND SHELTER IMMEDIATELY. GO TO A STURDY BUILDING THAT WILL WITHSTAND HIGH WINDS. AVOID ELECTRICAL APPLIANCES AND TELEPHONES.

IT WOULD BE A GOOD IDEA TO BRING YOUR CAR INSIDE A GARAGE AND TO SECURE LOOSE OBJECTS.

REMEMBER... A SEVERE THUNDERSTORM WARNING MEANS THAT A SEVERE THUNDERSTORM IS OCCURRING. THE SEVERE THUNDERSTORM HAS BEEN DETECTED BY THE DOPPLER RADAR OR REPORTED TO THE NATIONAL WEATHER SERVICE BY OUR SKYWARN SPOTTER NETWORK OR THE LOCAL LAW ENFORCEMENT AGENCY IN A PARTICULAR COUNTY.

A SEVERE THUNDERSTORM WATCH MEANS THAT CONDITIONS ARE RIGHT FOR SEVERE THUNDERSTORMS TO DEVELOP... BUT NONE HAVE BEEN OBSERVED. KEEP AN EYE ON THE SKY AND LISTEN TO COMMERCIAL BROADCASTS OR WEATHER RADIO FOR ANY SUBSEQUENT WARNINGS.

WHEN A SEVERE THUNDERSTORM WARNING IS ISSUED FOR YOUR LOCATION.... TREAT IT THE SAME AS YOU WOULD A TORNADO WARNING. SEVERE THUNDERSTORMS CAN PRODUCE DAMAGING WINDS... LARGE HAIL... DEADLY LIGHTNING... AND OCCASIONALLY TORNADOES.

FOR MORE TIPS ON BEING PREPARED IN CASE OF SEVERE WEATHER, PLEASE VISIT THE NWS-MEMPHIS WEBSITE ON PREPAREDNESS.

TOMORROW'S SEVERE WEATHER TOPIC WILL BE LIGHTNING.

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Another pattern shift and severe weather awareness campaign

A week ago, the Mid-South was just beginning a warm-up that would finally end a streak of cold and snowy weather that brought nearly 10" of powder/slush/ice since the first of the year. That pattern shift resulted in a very warm "spring-like" period this past week with temps in the 60s to lower 70s as high pressure dominated much of the central U.S.

This weekend, we are starting to see the overall pattern change again, though not to another brutally cold one. As we head towards March, a more progressive pattern will return with cold fronts every few days and temperature swings more typical of early spring - warmth ahead of frontal systems and brief cool snaps behind them.  This pattern also favors better chances of thunderstorms, so expect to see them in the forecast more often, rather than just rain (or heaven forbid, snow!).

The first front to have a noticeable effect on our weather will arrive Monday. Ahead of it, look for windy and warm conditions Sunday and Monday, followed by a quick cool-down with lows back in the 30s Tuesday and Wednesday mornings and seasonal daytime temperatures in the 50s. We'll warm up once again late in the week as yet another potentially potent front moves into the region Friday. Thunderstorms will be possible with both of these fronts this week, though the late week system seems to have more potential for thunder.

The timing of this pattern change is also appropriate as the Mid-South enters Severe Weather Awareness Week.  Each day this coming week, a different severe weather topic will be the focus. The National Weather Service, in conjunction with state Emergency Management Associations and media partners, will lead residents through safety topics and an education campaign to remind everyone of the importance of preparing for severe weather.  MemphisWeather.net will also participate by relaying information from the NWS and TEMA and answering your severe weather questions.  This week's topics will be:

Sunday - SKYWARN storm spotters
Monday - Flooding and Flash Floods
Tuesday - Lightning
Wednesday - Tornadoes, including a statewide tornado drill
Thursday - Severe Thunderstorms
Friday - NOAA Weather Radio and the Emergency Alert System

Finally, on Saturday (Feb. 26) at 10am, the NWS will be presenting their annual Memphis storm spotters course at the Agricenter.  Reservations are not required and teenagers are welcome and encouraged to attend.  Topics will include the basics of storm spotting, what to look for and where to look for it, and reporting your sightings to the NWS. Brief appearances are made by local TV meteorologists, as well as the local chapter of the American Meteorological Society/National Weather Association.

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Severe Weather Awareness Week begins Monday

Next week, MWN will be participating in severe weather awareness week with the National Weather Service and emergency management agencies, as well as local media. Various weather topics will highlighted throughout the week as we do our part to educate you on the threats associated with severe weather.


PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE MEMPHIS TN
915 AM CST FRI FEB 18 2011

...SEVERE WEATHER AWARENESS WEEK IN THE MID-SOUTH IS NEXT WEEK...

THE NATIONAL WEATHER SERVICE IN COOPERATION WITH EMERGENCY
MANAGEMENT AND THE MEDIA WILL PARTICIPATE IN SEVERE WEATHER
AWARENESS WEEK ACROSS TENNESSEE...ARKANSAS...AND MISSISSIPPI FROM
MONDAY...FEBRUARY 21ST THROUGH FRIDAY FEBRUARY 25TH.

THE NATIONAL WEATHER SERVICE AND THE MISSISSIPPI...ARKANSAS...AND
TENNESSEE EMERGENCY MANAGEMENT AGENCIES ARE AGAIN ASKING FOR YOUR
HELP IN SPREADING INFORMATION ABOUT THE THREAT OF SEVERE WEATHER AND
THE LIFE SAVING MEASURES TO BE TAKEN WHEN SEVERE WEATHER OCCURS.

SEVERE WEATHER WATCHES AND WARNINGS ARE INEFFECTIVE WHEN THE PUBLIC
DOES NOT RECEIVE THE MESSAGE OR DOES NOT KNOW HOW TO RESPOND TO
SEVERE WEATHER BY USING KNOWN AND EASY SEVERE WEATHER SAFETY
PROCEDURES TO PROTECT THEIR LIVES WHEN INCLEMENT WEATHER THREATENS.

WHETHER IN THE FORM OF SEVERE THUNDERSTORMS...TORNADOES...OR FLASH
FLOODS...SEVERE WEATHER CAN DEVELOP VERY QUICKLY. ONCE A TORNADO
APPROACHES...OR FLOODING DEVELOPS...IT IS TOO LATE TO START WORKING
ON THE PREPAREDNESS PLAN. WHEN SEVERE WEATHER DEVELOPS...AND WARNINGS
ARE ISSUED...WE MUST TAKE IMMEDIATE ACTION TO PROTECT OURSELVES.
PREPARING FOR SEVERE WEATHER IS THE THEME OF THIS PROGRAM.

THE PURPOSE OF SEVERE WEATHER AWARENESS WEEK IS TO DRAW ATTENTION
TO THE MANY ASPECTS OF SEVERE WEATHER WHICH AFFECT ALL OF US...TO
FOCUS ON SAFETY...AND TO LEARN WHAT TO DO WHEN HAZARDOUS
WEATHER THREATENS. AGAIN...SEVERE WEATHER AWARENESS WEEK IS FROM
MONDAY...FEBRUARY 21ST THROUGH FRIDAY FEBRUARY 25TH.

$$

Tired of winter? A hint of spring arrives very soon!

U.S. snow depth at midnight on Feb. 11, 2011 (Google Earth image - click for larger version)

After receiving 9.4" of snow in the last 33 days (as recorded at Memphis International Airport), Memphians are excited about the possibility of a lengthy warm spell.  This appears to be exactly what we have in store beginning Sunday and lasting right through next week.  The upper atmosphere is undergoing a major pattern shift this weekend which will bring a thaw to much of the central and eastern U.S. after record snowfall in many locations.  The map above shows snow depth across the United States as of midnight last night (Friday morning) in which 47 of the lower 48 states had snow.  For the Mid-South, the pattern shift will mean an extended period of high temperatures in the 60s  and milder conditions overnight, as indicated by the MWN Forecast.

The model graphics below show the temperatures at the 5,000-foot (850mb) level of the atmosphere, which are commonly used by forecasters to predict surface high temperatures.  The purple line is 0 degrees C (32 F, or the freezing level), while blue lines are sub freezing and red lines are above freezing.  Each line is +/- 3 degrees C from it's neighboring line, so the first red line next to the purple line is 3C (or about 37 F), the next one is 6C (or about 42 F), etc. The top graphic (click to enlarge) is the 5,000-foot temperatures last night (Thursday, Feb 10) at 6pm and the bottom graphic is the forecast for next Tuesday evening at 6pm (Feb. 15).  Notice that the freezing line (purple) was along the Gulf Coast last night and by Tuesday it will have retreated to the Great Lakes!  While blue lines encompassed much of the nation last night, by Tuesday, we're all in the red - a sure sign of a big warm-up!  I think we're all ready for a taste of spring.

850mb temperatures at 6pm Thursday, 2-10-11. The freezing line (purple) is on the Gulf Coast.

850mb temperature forecast for Tuesday, 2-15-11, at 6pm.
The freezing line (purple) is over the Great Lakes.

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Snowfall Accumulations from February 9, 2011

NWS-Memphis analysis of snowfall totals. Click for larger image.

NOAA experimental snowfall analysis for Feb. 9 snowfall. Click for larger image.

Below are the snowfall accumulations from yesterday's storm by county for the Memphis service area, as provided by NWS-Memphis.  The first map above is put together by the NWS-Memphis office based on actual snowfall totals received.  The second map is a new experimental snowfall analysis tool which also clearly shows the areas that received heavier snow.

County   Snowfall (inches)

In Missouri...
Dunklin........1-3
Pemiscot.......3-5

In Arkansas...
Clay...........3-5
Craighead......1-3
Crittenden.....2-5
cross..........2-4
Greene.........1-3
Lawrence.......2-6
Lee............7-8
Mississippi....1-3
Phillips.......M
Poinsett.......2-3
Randolph.......3-7
St. Francis....3-7

In Tennessee...
Carroll........2-4
Chester........2-3
Crockett.......1-2
Decatur........2-4
Dyer...........1
Fayette........2-4
Gibson.........1-2
Hardeman.......2-3
Hardin.........2
Haywood........2-3
Henderson......2-4
Henry..........1-3
Lake...........1-2
Lauderdale.....1-3
McNairy........2-3
Madison........2
Obion..........2-3
Shelby.........3-5
Tipton.........3
Weakley........1-2

In Mississippi...
Alcorn.........2-3
Benton.........4-5
Calhoun........M
Chickasaw......M
Coahoma........M
DeSoto.........4-6
Itawamba.......2-3
Lafayette......4-6
Lee............3
Marshall.......M
Monroe.........4
Panola.........4-5
Pontotoc.......4
Prentiss.......3
Quitman........M
Tallahatchie...5
Tate...........M
Tippah.........3-4
Tishomingo.....2-4
Tunica.........6
Union..........4
Yalobusha......M

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Top 10 snowfalls at Memphis

Below are the snowiest winters in recorded Memphis history, as well as the biggest "storms" by snowfall amount.  Memphis has officially received 6.6" of snow so far this winter (2010-2011). We are a ways from reaching the top 10!

Top 10 Snowiest Winters in Memphis
1. 25.1 inches, 1917-18
2. 24, 1891-92
3. 23.8, 1967-68
4. 20.7, 1984-85
5. 20.5, 1959-60
6. 18.2, 1909-10
7. 17.5, 1904-05
8. 16.4, 1947-48
9. 15.6, 1894-95
10. 15.6, 1914-15

Top 10 Biggest Snows in Memphis History
1. 18 inches, March 17, 1892
2. 17.3 inches, March 21-23, 1968
3. 14.3 inches, Dec. 22, 1963
4. 11.8 inches, Jan. 16, 1948
5. 9.6 inches, Jan. 7, 1884
6. 9.6 inches, Feb. 3, 1886
7. 9 inches, March 7, 1875
8. 8.5 inches, Jan. 4, 1878
9. 8.5 inches, Dec. 7-8, 1917
10. 8.1 inches, Jan. 3, 1985

Source: National Weather Service

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Weather 102: Snow ratios and the liquid water equivalent

A couple of days ago I posted a "Weather 102" entry on the basics of the wet-bulb effect and how it plays into the onset of a winter precipitation event. Tonight, I'll continue the "Weather 102" series by providing some basic information on snow ratios and the liquid water that goes into producing snow.

Most of the time when it snows in the Mid-South, we receive a wet, heavy, "sticky" snow that makes for good snowballs, snowmen, and other snow concoctions and slushy streets if it comes down hard enough. Rarely do we see snow that blows freely once it reaches the ground and produces small drifts in the wind.  This is much more common in northern locations. Have you ever thought about why?

In basic terms, it comes down to the water content of the snow and the temperature of the air in which those water molecules freeze (which happens to be much below the expected 0 C/32 F) and subsequently fall through.  The term typically used to describe the water content of snow is the snow ratio, or more accurately snow to liquid water ratio.  The widely-accepted average snow ratio is 10:1.  In other words, for every 10" of snow that falls, when melted, an inch of liquid water results.  Thus, going the other direction, if a snowfall is expected to be produced from .25" of liquid water, 2.5" of snow would result.  In wet snows, the snow ratio may be lower - say 8:1 or 9:1.  Thus, the same .25" of liquid would produce 2.0-2.25" of snow (lower accumulation, but wetter snow).  With dry snow, the ratio goes up, say to 15:1 or 20:1.  Again, given the same .25" of liquid water, the snow accumulation with a dry snow may be 4-5" (higher accumulation, drier snow).

What determines the snow ratio?  Without getting too detailed (I'll save that for Weather 103 or 104!), the temperature of the column of air the snow encounters has a great deal to do with it. In the Mid-South, we typically see snow with surface temperatures in the 28-34 degree range. and temperatures aloft (in the levels below where the snow forms) below freezing but not exceptionally cold. These "warmer" temperatures, especially with a surface temperature near freezing or above, promote high water content in the snow and lower snow ratios (8:1 to 11:1). In addition, wetter snowflakes tend to stick together as they fall and bump into one another, creating what appears to be very large flakes, which are actually multiple flakes aggregated together. Where temperatures are colder at the surface (mid 20s or lower) and aloft, the snow is drier, with lower water content and higher snow ratios. This is more typical up north where it is usually colder when it snows. In addition, drier flakes do not stick together as easily when they fall, so we observe many more smaller flakes at the ground.

So, for tomorrow's snow event, temperatures will be colder than the past few snow events and conditions in the lowest few thousand feet of the atmosphere will be more conducive to a drier snow. The models are pointing to snow ratios in the 15:1 range. Thus, when calculating the amount of snow we will receive tomorrow, I am using a ratio of about 15:1.  With Monday's snow, it was closer to 9:1 as temperatures were 32-33 degrees. Wednesday's snow won't be nearly as good for packing snowballs, but it might mean that the roads are better able to handle it, since it won't stick so much as just blow around.  We'll see if I am right tomorrow!

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Winter Storm Warnings and Advisories posted for Wednesday

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE MEMPHIS TN
409 PM CST TUE FEB 8 2011

...ANOTHER WINTER STORM TO BRING ACCUMULATING SNOW TO THE MID-SOUTH WEDNESDAY AND WEDNESDAY EVENING...

.LOW PRESSURE WILL DEVELOP ALONG THE TEXAS GULF COAST ON WEDNESDAY AND MOVE EASTWARD INTO CENTRAL FLORIDA BY THURSDAY MORNING. DEEP GULF MOISTURE WILL OVERSPREAD MUCH OF THE MID-SOUTH BY WEDNESDAY MORNING COMBINING WITH ARCTIC AIR THAT WILL BE IN PLACE.

AS A RESULT...SNOW IS EXPECTED TO DEVELOP WEDNESDAY MORNING ACROSS WESTERN SECTIONS OF THE REGION AND SPREAD EASTWARD THROUGH THE DAY. HEAVIER SNOW SHOULD DEVELOP BY WEDNESDAY AFTERNOON AND CONTINUE THROUGH WEDNESDAY EVENING. SEVERAL INCHES OF SNOW IS EXPECTED ACROSS THE WARNING AREA BEFORE THE SNOW TAPERS OFF LATE WEDNESDAY EVENING.

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CRITTENDEN-
INCLUDING THE CITIES OF...WEST MEMPHIS
409 PM CST TUE FEB 8 2011

...WINTER STORM WARNING IN EFFECT FROM 6 AM TO 9 PM CST WEDNESDAY...

THE NATIONAL WEATHER SERVICE IN MEMPHIS HAS ISSUED A WINTER STORM WARNING FOR SNOW...WHICH IS IN EFFECT FROM 6 AM TO 9 PM CST WEDNESDAY. THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

* SNOW ACCUMULATIONS: 2 TO 4 INCHES.

* TIMING: WEDNESDAY MORNING THROUGH WEDNESDAY EVENING.

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DESOTO-MARSHALL-SHELBY-
INCLUDING THE CITIES OF...SOUTHAVEN...OLIVE BRANCH...BARTLETT...GERMANTOWN...COLLIERVILLE...MEMPHIS...MILLINGTON
409 PM CST TUE FEB 8 2011

...WINTER STORM WARNING IN EFFECT FROM NOON WEDNESDAY TO MIDNIGHT CST WEDNESDAY NIGHT...

THE NATIONAL WEATHER SERVICE IN MEMPHIS HAS ISSUED A WINTER STORM WARNING FOR SNOW... WHICH IS IN EFFECT FROM NOON WEDNESDAY TO MIDNIGHT CST WEDNESDAY NIGHT. THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

* SNOW ACCUMULATIONS: 2 TO 4 INCHES.

* TIMING: WEDNESDAY MORNING THROUGH WEDNESDAY EVENING.

* IMPACTS: SIGNIFICANT SNOW ACCUMULATIONS COMBINED WITH TEMPERATURES SEVERAL DEGREES BELOW FREEZING FOR THE DURATION OF THE EVENT WILL LIKELY LEAD TO SNOW COVERED ROADS AND HAZARDOUS DRIVING CONDITIONS. WINDS MAY ALSO GUSTS BETWEEN 15 AND 25 MPH ACROSS PORTIONS OF THE AREA WHICH WOULD LEAD TO THE POTENTIAL FOR BLOWING AND DRIFTING SNOW.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WARNING FOR HEAVY SNOW MEANS SEVERE WINTER WEATHER CONDITIONS ARE EXPECTED OR OCCURRING. SIGNIFICANT AMOUNTS OF SNOW ARE FORECAST THAT WILL MAKE TRAVEL DANGEROUS. ONLY TRAVEL IN AN EMERGENCY. IF YOU MUST TRAVEL... KEEP AN EXTRA FLASHLIGHT... FOOD... AND WATER IN YOUR VEHICLE IN CASE OF AN EMERGENCY.

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TIPTON-FAYETTE-
INCLUDING THE CITIES OF...COVINGTON...SOMERVILLE
409 PM CST TUE FEB 8 2011

...WINTER WEATHER ADVISORY IN EFFECT FROM NOON WEDNESDAY TO MIDNIGHT CST WEDNESDAY NIGHT...

THE NATIONAL WEATHER SERVICE IN MEMPHIS HAS ISSUED A WINTER WEATHER ADVISORY FOR SNOW...WHICH IS IN EFFECT FROM NOON WEDNESDAY TO MIDNIGHT CST WEDNESDAY NIGHT. THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

* SNOW ACCUMULATIONS: 1 TO 2 INCHES.

* TIMING: WEDNESDAY MORNING THROUGH WEDNESDAY EVENING.

* IMPACTS: LIGHT SNOW ACCUMULATIONS COMBINED WITH TEMPERATURES SEVERAL DEGREES BELOW FREEZING FOR THE DURATION OF THE EVENT WILL LIKELY LEAD TO SNOW COVERED ROADS AND HAZARDOUS DRIVING CONDITIONS.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER WEATHER ADVISORY FOR SNOW MEANS THAT PERIODS OF SNOW WILL CAUSE PRIMARILY TRAVEL DIFFICULTIES. BE PREPARED FOR SNOW COVERED ROADS AND LIMITED VISIBILITIES... AND USE CAUTION WHILE DRIVING.

Tuesday mid-day update on Wednesday's snow event

Not a lot has changed since last night's post as of this time. The GFS model still seems to be an outlier, predicting about an inch of snow for Memphis with more south. The other models are clustering around of solution of 2-4" accumulation.  Timing of the snow in the metro area now appears to be about noon through midnight Wednesday with the best chance at accumulation in the late afternoon hours, prior to rush hour. Most of the snow we get will likely be on the ground by 7pm with light snow showers or flurries continuing through the night. The highest snowfall totals in this region of the country will be south and west of Memphis, with an axis of heavy snow likely across central AR into northwest MS.  My forecast of 2-4" of snow stands for now with the higher end of that range likely seen to the south of the city and the lower end to the north.

To give you an idea of where this storm is coming from, and the huge portion of the country that it is affecting, check out the map below (taken at noon today) showing the forecast track of the low pressure system responsible for the snow and the huge area covered by winter weather watches, warnings, and advisories (color-filled counties from NM/CO all the way to AL):

The next map shows the probabilities of a 4"+ snowfall from 6am Wednesday to 6am Thursday. This shows the axis of heaviest snow from southeast OK through AR to northwest MS. Memphis is right on the edge of a "moderate probability" (40%) of 4" of snow. I expect some place in central AR, near or south of Little Rock, is going to see a heavy snow event of 8" or more!

Probabilities of a 4" snow event from the National Weather Service (click image for larger image)

Finally, from the NAM model, the expected snow totals FROM THIS MODEL are shown below. While it seems to be overdoing it for places to our west, I think it's not as bad for our area and generally shows 2-4" for the metro counties (light blue and yellow colors).

Tuesday 6am NAM computer model output showing 2-4" over Memphis (click image for larger view)

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Much anticipated first call for Wednesday's snow from MWN

Somehow today's snowfall caught many folks seemingly by surprise, despite the good coverage and forecasting of it by weather folks across the area. While totals north of the metro were likely higher than most of us anticipated (northwest TN received anywhere from 3-6"+), widespread 1-2" amounts within the Memphis area were pretty much dead on with forecasts and the timing forecast was great as well.  Rain changed to snow in the 7-9am timeframe, depending on the side of the city that you call home and accumulating snow was about done by 11am, though light snow showers and flurries continued into the early afternoon.

I believe the reason people were caught off-guard by today's snow is the same reason coaches don't want their sports teams looking past the next game - they might overlook a seemingly less worthy opponent and get caught flat-footed. In this case, there's been so much talk about the Wednesday snow (for nearly a week now) that the Monday storm got overlooked. Now that today's event is done, let's go ahead and start talking about it's more-hyped big brother. First the knowns:

1) Weak low pressure at the surface and aloft will move out of Texas and along the Gulf coast and will generally be weakening as it does.
2) The airmass leading into this system is colder than today's was, thus we will have an all-snow event. There will be no transition from rain and no ice expected.
3) Accumulation is pretty much a given (the amount is not) and the snow will be somewhat drier than today's wet good-packing snow and will not be quite as good for snowmen!
4) Someplace in Arkansas, probably in the west-central portion of the state, is going to get dumped on.  I wouldn't be surprised to see a foot of snow somewhere over there. Closer to home, snow will likely be deeper as you go SOUTH, into northwest MS, than north into west TN.
5) Timing seems to be fairly similar among all models with the accumulating snow expected from mid-afternoon Wednesday through midnight or shortly after - roughly 9 hours of snow.
6) A Winter Storm Watch has been posted for much of AR, west TN, and northwest MS for Wednesday.

What is not a given, and would answer everybody's question - "How much?" - is this: computer models are generally falling into one of two trains of thought regarding the strength of the low and snowfall amounts. These two "camps" have been bullheaded about staying in their respective camps for some time and farther apart than I would like as we get within 48 hours of the event commencing.

One train of thought, which is led by the well-known and respected GFS model, shows a very weak system passing well to our south and bringing only an inch or snow of snow.  One of the better mid-range models, the European (or ECMWF), also shows a pretty weak system as of the past couple of days, but seems to be bringing a little more snow than the GFS, even given it's lack of punch.  (It should be noted that last week the GFS showed accumulations of a foot or more before it flip-flopped back to the low end of the spectrum.)

The second train of thought followed by the well-known NAM (which has seemed to overestimate snow amounts the past few times) and other higher-resolution models, as well as the mid-range Canadian GEM, is stronger with the upper-level low, and thus dumps more precipitation on the region. The range from these models seems to be 3-5".

So, given all of this, my initial estimate for the metro area is 2-4", beginning after 2pm Wednesday and ending around midnight (12:00am Thursday). Higher amounts in that range will generally be over northwest MS, while lower amounts would be north of the big city. I'll update as conditions warrant and certainly will be covering this storm on Facebook and Twitter just as with the others in this endless string of winter!

As a side note: a rapid and noticeable warming trend appears to be taking shape heading into the weekend. It appears as though it may be a fairly long-lasting one as well!  Perhaps this will be the last Mid-South snowstorm of the winter... we'll see!

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NWS: Winter Storm Watch issued for Wednesday

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE MEMPHIS TN
329 PM CST MON FEB 7 2011

...ANOTHER WINTER STORM TO BRING ACCUMULATING SNOW TO THE MID-SOUTH WEDNESDAY AND WEDNESDAY NIGHT...

.A STRONG MID LEVEL SHORTWAVE OVER THE PACIFIC NORTHWEST THIS AFTERNOON WILL DIVE SOUTHEAST ACROSS THE CENTRAL PLAINS AND INTO THE MID SOUTH BY MID-WEEK. THIS UPPER SYSTEM WILL HELP TO INDUCE SURFACE LOW PRESSURE ALONG THE NORTHWEST GULF COAST WHICH WILL MOVE EASTWARD THROUGH THURSDAY. ABUNDANT GULF MOISTURE WILL OVERSPREAD MUCH OF THE FORECAST AREA BY WEDNESDAY MORNING. AN ARCTIC AIRMASS SHOULD BE IN PLACE ACROSS THE MID SOUTH PRIOR TO THE ONSET OF PRECIPITATION. SNOW SHOULD DEVELOP WEDNESDAY MORNING ACROSS WESTERN SECTIONS AND SPREAD EAST THROUGH THE DAY. HEAVIER SNOW SHOULD DEVELOP OVER THE WATCH AREA BY WEDNESDAY AFTERNOON AND CONTINUE THROUGH WEDNESDAY EVENING. SEVERAL INCHES OF SNOW WILL BE POSSIBLE BEFORE SNOW ENDS THURSDAY MORNING.

...WINTER STORM WATCH IN EFFECT FROM WEDNESDAY MORNING THROUGH
LATE WEDNESDAY NIGHT...

THE NATIONAL WEATHER SERVICE IN MEMPHIS HAS ISSUED A WINTER STORM WATCH... WHICH IS IN EFFECT FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT.

* SNOW/SLEET/ICE ACCUMULATIONS: GREATER THAN 4 INCHES POSSIBLE.

* TIMING: WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT.

* IMPACTS: SIGNIFICANT SNOW ACCUMULATIONS WILL BE POSSIBLE ACROSS THE WINTER STORM WATCH AREA. TEMPERATURES SHOULD REMAIN SEVERAL DEGREES BELOW FREEZING FOR THE DURATION OF THE SNOW EVENT. THIS WILL LIKELY LEAD TO SNOW COVERED ROADS AND HAZARDOUS DRIVING CONDITIONS IN AREAS THAT RECEIVE SIGNIFICANT SNOW ACCUMULATIONS. WINDS MAY ALSO GUSTS BETWEEN 15 AND 25 MPH ACROSS PORTIONS OF THE AREA WHICH WOULD LEAD TO THE POTENTIAL FOR BLOWING AND DRIFTING SNOW.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WATCH MEANS THERE IS A POTENTIAL FOR SIGNIFICANT SNOW... SLEET... OR ICE ACCUMULATIONS THAT MAY IMPACT TRAVEL. CONTINUE TO MONITOR THE LATEST FORECASTS.

More snow - details on Monday's system and an initial look at mid-week

The National Weather Service in Memphis has issued a Winter Weather Advisory for all of east AR, most of west TN, and DeSoto and Tunica Counties in northwest MS for Monday. East of the river, including the Memphis metro area, this advisory is in effect from 6am to 6pm.  The map to the left (click for larger version) shows the Advisory area and expected snow amounts.

Above normal temperatures exist across the Memphis metropolitan area this afternoon with highs in the 50s today, but a cold front will move through this evening, bringing wind around to the north. In addition, an upper-level disturbance over Texas will approach the area with an area of precipitation.  As temperatures fall overnight, light rain will begin after midnight, changing to light snow around dawn as the mercury reaches the middle 30s. By 9am, we should see all precipitation falling in the form of snow. Snow could fall at a pretty good clip during the morning hours before tapering off to flurries during the afternoon. I expect temperatures to remain in the low to mid 30s all day Monday with a north wind making it feel 20-25 degrees colder than this afternoon. Snow accumulations will likely be around 1-1.5" in the city and surrounding suburbs by early afternoon. Roads will likely become hazardous and slushy, especially secondary streets.

The next winter weather storm will move through the region Wednesday. This storm system has been hyped (or shall I say discussed) since the middle of last week when mid-range models went nuts with snow amounts and the degree of cold air behind it. As expected, those same models have moderated considerably, though another bout of winter weather appears likely. We'll monitor the situation and bring you the latest, especially after tomorrow's snow ends, but right now there still appears to be the potential for accumulating snow of a few inches late Wednesday into early Thursday. The good news is, after that round of weather, signs point towards a less active and warmer pattern heading into next weekend!

MWN will continue to bring you the latest information on the web, Facebook, and Twitter. School closings, should they be required, will be posted on the blog (click the Metro School Closings tab at top).

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Weather 102: Basics on the wet-bulb process and why you should care

Warning: this post is a little technical and lengthy! I've tried to simplify it for the average reader.  Let me know how I've done!

In developing winter weather scenarios, meteorologists (often not in front of you, lest they forever be known as weather geeks!) will often refer to the "wet-bulb temperature," or the wet-bulb process.  In it's simplest form, the wet-bulb temperature is a combination of the air temperature (or what is actually called the dry-bulb temperature) and the amount of water vapor in the air, typically measured by the dewpoint temperature.  Temperature and dewpoint are terms you have probably heard before.  Dewpoint is a measure of the amount of moisture in the air, which, if the air were cooled to that temperature, there would be 100% relative humidity.  So, if the temperature is 40 degrees and the humidity were 55%, the dewpoint would be 25.  In other words, cooling the air down to 25 degrees would produce 100% humidity.

The wet-bulb, on the other hand, falls between the air temperature and the dewpoint temperature.  It is defined as the lowest temperature that can be reached by evaporation only.  As rain/snow falls from clouds, evaporation takes place as the precipitation falls into drier air.  As the evaporation occurs, the amount of moisture in the air goes up, the dewpoint increases, and the temperature decreases, bringing them closer together.

"Wet-bulbbing" is important in winter weather scenarios (and actually all precipitation onset situations) because as the initial precipitation falls from clouds, it first saturates the atmosphere it is falling into through evaporation.  This process (called "evaporative cooling") lowers the temperature and increases the dewpoint.  If the temperature lowers to a point below freezing (when the wet-bulb temperature is below freezing), a temperature in the upper 30s could end up falling into the lower 30s and producing winter weather!

An example of the wet-bulb process can be seen as precipitation began on January 9, 2011 in the graph of temperature and dewpoint in Bartlett below.  Notice the temperature (white) fall and dewpoint (yellow) quickly rise between 6-8pm.  The 30 degree temperature ended up in the mid 20s and the dewpoint rose from the single digits to the lower 20s.  Precipitation falling shortly after 6pm did not reach the ground, instead evaporating and causing the wet-bulb process to occur. By 8pm, moderate snow was reaching the ground.  The difference between the temperature and dewpoint until 6pm also delayed the initial onset of the precipitation, likely resulting in virga (precipitation seen falling from the clouds but evaporating before reaching the surface).

The wet-bulb process occurred between 6-8pm on January 9, 2011.

Why bring this up now? Well, the process is occurring right now in the Memphis area!  Very light precipitation is falling from the clouds and evaporating. The difference between temperature and dewpoint is about 10 degrees (38 and 28). Through the evening, those two numbers will approach each other (nearing the wet-bulb temperature) and light rain will change to light snow due to the surface temperature falling!  Watch for it on the WXLIVE! graphical page, noting the temp/dewpoint graph.

You can get an idea of what the wet-bulb temperature is by moving air over wet skin. Are you cold when you first get out of the shower? In essence, you're experiencing the wet-bulb temperature of your bathroom!  The air feels cooler when exposed to a wet surface - you!

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