Wednesday evening severe weather update: overnight and Thursday

The Memphis metro is under a Tornado Watch until 3am. Though the tornado threat in the immediate metro is low, it is not zero, as storms that move into the region will encounter a very dynamic wind environment with strong low level wind blowing at highway speeds and a favorable upper level jet stream that will support strong to severe storms.

Tornado Watch #63 valid until 3am CDT. The highest tornado threat is south of the metro.

The main round of heavy rain and thunderstorms will arrive by 10pm with rain and storms continuing through much of the night, moving out by dawn. Total rainfall overnight will likely be around 2". The primary severe weather threats will be damaging wind (as wind near 3000' will be blowing at 60-70 mph and could easily be transported to the surface by a thunderstorm), large hail, copious lightning (put the thundershirt on Fido if you need to), and flash flooding.

We highly recommend having a way of receiving severe weather warnings overnight, a method that will wake you up if dangerous weather is headed your way. A NOAA Weather Radio will do the job, as will reliable severe weather warning apps. We obviously highly recommend the MemphisWeather.net app with StormWatch+ activated and setup to push severe weather alerts to your phone (video: Configuring StormWatch+). StormWatch+ will wake you up, but only if your programmed location is under a Severe Thunderstorm or Tornado Warning. (Link: "Will my phone alert me if I silence it?") Links are at the bottom of this post for info or download. In addition, cell phones should be charging before you go to bed, just in case power outages occur before you have a good charge.

On Thursday, a good part of the day will likely be dry as the atmosphere re-energizes ahead of the next round of potential severe weather. Temperatures will soar into the upper 70s by afternoon with dewpoints in the mid 60s. As a cold front moves into the region, the instability (reflected in CAPE [Convective Available Potential Energy] values of 1500-2000 J/kg, which is plenty sufficient for strong storms) created by the warm, humid air will be lifted by the approach of the front and thunderstorms are expected to develop. Once again, wind energy will be sufficient for strong to severe thunderstorms to form. These storms are likely to be more of the supercell variety, which means the primary threats will be large hail, damaging wind, and potentially tornadoes. The area of most concern is near and east of the Mississippi River, including the metro, from mid-afternoon through the evening. These storms will also be capable of producing torrential rain in their path.

Once again, we recommend keeping a close eye on the weather tomorrow afternoon and evening in particular, and be ready to quickly heed any warnings that are issued. Also, consider your normal afternoon routines for picking up kids and/or commuting home in case storms are ongoing at those times.

An Enhanced Risk (3/5) of severe weather is forecast for most of the metro, where damaging wind, large hail, and a tornado are all possible from mid-afternoon through the evening.

Once the cold front passes in the evening hours (exact time TBD), the severe weather threat ends and we'll be heading into a stretch of cooler, drier days that include the first weekend in April.

Follow MWN on social media via the links below for the latest information and live nowcasting during severe weather events. You can also follow our Twitter feed via the MWN mobile app.

Erik Proseus
MWN Meteorologist

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March out like a lion! Heavy rain/severe weather threats end the month

Pleasant spring weather gives way to heavy spring rain and a few strong thunderstorms as March goes out like a lion! Already with a foot of rain for the month (12.01"), Memphis International Airport has recorded its fourth wettest March on record. If the forecast amount of rainfall occurs in the next 48 hours, March 2016 will be the wettest on record, eclipsing the current "high water mark" of 13.04" set in 1927. Let's get into the details.

The setup

High pressure that has been controlling our weather for a few days moves east of the region tonight, turning our wind to a southerly direction tomorrow as "double barrel" low pressure forms in the Plains, with one center of the low in Nebraska and another moving east across north Texas over the next 24 hours. That will setup a scenario in which abundant moisture will be pulled north from the Gulf of Mexico on a developing low level jet stream (in the lowest 2000-5000' of the atmosphere) and increasingly gusty southerly surface wind. With plenty of moisture in place, upper level disturbances that move through the area ahead of the low pressure systems will help to initiate and focus rain and thunderstorms across the region.

The surface setup at mid-day Wednesday shows the double lows over the Plains and widespread rain and thunderstorms ahead of the system, including over the Mid-South.

Wednesday/Wednesday Night

This process will begin tomorrow with rain and some thunderstorms breaking out over the area, as well as moving in from the southwest, mainly during the afternoon hours. However, the focus of one of these upper level disturbances will be moving out of the ArkLaMiss region east into north MS Wednesday evening into Wednesday night, resulting in heavy rainfall and the threat of a few strong storms. In fact, the heaviest rain over the next couple of days is expected Wednesday night.

The Storm Prediction Center has placed most of the metro in a Slight Risk (category 2/5) of severe storms for Wednesday into Wednesday night when a few storms will be capable of large hail or damaging wind (see graphic below). (In fact, a large area from the central Gulf Coast all the way to the Corn Belt are under a Slight Risk as severe storms could be widespread.)

A Slight Risk of severe weather (yellow, category 2/5) covers most of the metro for Wednesday and Wednesday night.

Thursday

Once the main disturbance passes by to our east late Wednesday night, there will not be as strong of a focus for rain and storms heading into early Thursday. However, with the lows still to our west and their cold front approaching, we will still be in the "warm sector" of the storm system with southerly wind flow over the area. With less widespread rain, instability will increase markedly Thursday as temperatures warm well into the 70s and dewpoints (a measure of near-surface moisture) will rise into the 60s. This combination of ingredients will mean the threat of storms remains possible, particularly as the cold front itself approaches late Thursday. The index typically most widely used to measure instability is CAPE, or Convective Available Potential Energy - energy in the atmosphere that is "available" to produce convection, or thunderstorms. The graphic below shows forecast CAPE values for Memphis from a series of model runs called an ensemble.

A model "ensemble" means that the model was run numerous times with small "tweaks" to the way the model is run. In this case, the GFS model was run numerous times and the graphic displays the Convective Available Potential Energy (CAPE) values for Memphis for Wednesday and Thursday from each of those model runs. CAPE is a measure of instability of "storm fuel". Values of 200-300 J/kg on Wednesday are sufficient for thunderstorms, but values of 1200-1500 J/kg on Thursday afternoon are more supportive of strong storms.

Though we expect less overall rain Thursday than Wednesday night, storms are expected to be scattered to numerous, and stronger (due to higher CAPE), especially mid-day through the afternoon. Though SPC only has the metro in a Marginal Risk (category 1/5) for Thursday as of this post, I wouldn't be surprised to see that raised tomorrow or Thursday if current forecast conditions remain favorable. By late Thursday (late afternoon or early evening), the cold front will pass through and our rain and thunderstorm chances will end, beginning an extended period of dry and cooler, but seasonal, weather  heading into the weekend.

Heavy rain threat

As for the heavy rain threat, the greatest threat over the region, with particular emphasis on north Mississippi, is Wednesday after dark. On Thursday, very heavy rainfall will also be possible in localized areas under storms, but the threat won't be as widespread. Flash Flood Watches are in effect for all of north MS from Wednesday afternoon through Thursday (see graphic below).

Flash Flood Watches are in effect for a large area south of Memphis through Thursday.

Total rainfall amounts will likely be well over an inch in most areas of the region with 2-4" amounts likely in north MS. Below are model simulations of total rainfall for Memphis, as well as the NOAA precipitation forecast for the Mid-South.

Another look at the GFS Ensemble model data (similar to above), only this time for total rainfall. You'll notice that the mean, or average of all of the models, is about 2 1/4" of rain in Memphis, while the primary GFS model is indicating about an inch less than that. The range of values provided gives an idea of the range of scenarios possible. A "clustering" of data values provides higher forecaster confidence in a given scenario.  In this case, most scenarios indicate 1.5-2.5" of rain.

NOAA's Weather Prediction Center forecast rainfall amounts through Friday morning. Graphic courtesy WxBell.

Keep the umbrella handy the next couple of days, but be thankful that we'll get a good pollen-washing rain! And keep a close eye on the MWN Forecast and severe weather updates the next couple of days in case strong storms develop and move towards the Memphis metro.

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador

Meteorologist Erik Proseus is an NWA Digital Seal Holder

MWN meteorologist awarded national Seal of Approval

MemphisWeather.net is proud to announce that meteorologist Erik Proseus has been awarded the Digital Seal of Approval by the National Weather Association (NWA). Similar to the television broadcaster Seal of Approval, the Digital Seal is awarded to meteorologists who provide content via digital means, rather than via over-the-air broadcast. Since the program's inception in 2014, only four individuals nationwide have earned this distinction.

In order to be awarded the Digital Seal, applicants must complete all steps in a rigorous process, which includes acceptance into the application process by the NWA Executive Director, passing a 100-question exam covering all aspects of meteorology with a score of at least 80%, receiving high marks on a series of blog posts or multimedia webcast submissions by a national expert panel, and receiving final approval from the NWA President. A digital seal panel evaluates applicants blog post or webcast content on communication skills, use of graphics, meteorological competency, flow of presentation, use of terminology, and a "Feature" (educational or editorial) article.

“The Digital Seal of Approval was created by the National Weather Association to provide a means for the public to recognize trusted sources in the weather industry that provide information in the digital space,” stated Proseus. “I’m honored to be one of the first in the nation to earn this distinction and look forward to continuing to provide the best possible forecasts, as well as educating the public on weather hazards that affect Memphis and the Mid-South, and how to remain safe when they threaten.”

From the National Weather Association:
The public deserves the most accurate and timely weather forecast and warning information, in terms they can understand, to take appropriate action. For quality of life and the safety of all, weathercasters and other media representatives should commit to provide and continually improve this service. The NWA Broadcast Meteorology Committee promotes the development of quality television, radio and internet weathercasting among NWA members. Through the NWA Seal of Approval program, the NWA grants television/radio and digital Seals of Approval to NWA member weathercasters in the broadcast media (TV/Radio Seal) and in cyberspace (Digital Seal) who meet or exceed standards set by the NWA.


About Erik Proseus:
Erik is the owner of Cirrus Weather Solutions, LLC - a private meteorological firm based in Bartlett, TN, webmaster and meteorologist for MemphisWeather.net (MWN) and JacksonWeather.net, author of the MWN Blog, and social media connoisseur. He has made Memphis and Mid-South weather and climate his career, hobby, and passion for over 20 years. Having lived in the region since childhood, he knows the often-complicated weather patterns of the Mid-South well and relays his knowledge through various social and electronic channels, while providing a vast array of weather information, products, and services on MemphisWeather.net.

MWN is the official weather provider for the Memphis in May International Festival, the Memphis Redbirds AAA baseball team, and the Levitt Shell Summer Concert Series, as well as other smaller organizations and events. Erik's mission through Cirrus Weather Solutions, LLC is to use his meteorological expertise and honed communication skills to prepare, inform, and educate the public on current, future, and past weather conditions and events. The result has been the growth of the MemphisWeather.net social following to nearly 30,000 users who rely on the hyper-local reporting and no-nonsense, no-hype approach provided by MWN.

Erik also conceptualized and developed the StormWatch+ brand, which includes an all-weather alerting utility that pushes National Weather Service inclement weather alerts to smartphone apps based on the user's requested locations and preferences.

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Early spring cold front brings a chance of strong storms

Warm and windy conditions precede the next big frontal system to move through the region. The parent low pressure system has already dumped inches of snow, accompanies by very strong wind, in Colorado, which has prompted Blizzard Warnings in the northeastern portion of the state and the closure of the the Denver Airport this afternoon!

That low will move from the Front Range into the Midwest and Great Lakes regions as it drags a cold front across the Plains tonight and into the Mississippi River Valley by early Thursday. A line of strong storms is expected to form this evening in far eastern OK south toward the Dallas metroplex, then move east across AR overnight.

Locally: thunderstorms early Thursday

With respect to the Mid-South, and specifically the Memphis metro, the best thing we have going for us as this system approaches is timing. Fortunately, the strongest forcing, or lift, associated with the approach of the cold front arrives around our diurnal minimum - meaning at the coolest part of the day, in the early morning hours. A round of showers and thunderstorms is still expected early Thursday morning, but the severity should be on the low end.

The upper level trough that is driving the front and its associated mid and upper level wind pattern is strong, but without the aid of very buoyant air (meaning it is very warm and will rise quickly once forced upwards by a cold front), the strength of the storms should be kept in check. A few strong storms with straight-line wind of 50+ mph is possible, but the tornado and hail threat will be very low with these storms. Plus, as quickly as it moves through (perhaps in just a few hours), downpours could be heavy but a prolonged heavy rain event that produces flooding is also not expected. Rainfall totals from this system, which exits the metro by late morning, should be generally under an inch.

The Storm Prediction Center places the majority of the metro in a "Marginal Risk" (category 1 of 5) of severe storms for late tonight and early Thursday morning. (The reason we are outlooked in a Marginal Risk in both the Day 1 and Day 2 outlooks, as shown below, is because the SPC "day" starts and ends at 6am. Thus, there is a low-end severe risk west of the Mississippi River before 6am and a similar risk east of the river after 6am.)

A Marginal (category 1/5) Risk of severe storms is forecast generally from the metro westward for late tonight (early Thursday) as a few scattered strong storms are possible towards daybreak. A higher risk is indicated to our west as storms in AR lose strength during the early morning hours Thursday.

A Marginal (category 1/5) Risk of severe storms is forecast generally from the metro eastward for Thursday morning after 6am as a few scattered strong storms are possible during the morning hours. A higher is indicated to the east of the metro as the storms move into a more favorable environment.

You'll notice that higher risk categories are "outlooked" for areas west and east of the metro. This isn't because we have bluffs or a Pyramid! It simply reflects the timing of the storms' arrival. Late tonight, the storms will be stronger to our west and diminishing in strength after midnight as they get closer and lose the heating of the day that contributes to their strength. Later, after the storms move east of us Thursday afternoon, they will again gain strength as they arrive in an atmosphere that has benefited from Thursday's heating of the day. It's all about the timing in this case!

Bottom line it for me!

What: Showers and thunderstorms ahead of an early spring cold front
Where: The entire Memphis metro
When: Between 5-11am Thursday
How strong: A few storms could have strong wind and localized downpours

Expect wind to shift to the west by late morning and remain gusty Thursday with temperatures in the mid 50s to lower 60s and partly sunny skies by afternoon. Temperatures will drop back down into the mid to upper 30s Friday morning outside the urban core. Friday and Saturday will be seasonal with good weather expected for Saturday morning egg hunts.

Easter Sunday brings a return of southerly moisture and warmth with warm temperatures but increasing chances of showers and thunderstorms again by afternoon and evening. Early morning worship services or egg hunts should see dry and mild conditions.

Erik Proseus
MWN Meteorologist

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Meet StormWatch+, your NEW national weather app!

As many of our loyal readers know, a couple years ago we "un-bundled" the StormWatch+ severe weather alerting technology from the MemphisWeather.net brand and created a national iOS app called, aptly, StormWatch+. The centerpiece of the app was the push notification alerts, but it also included a basic radar display, local conditions, and the NWS forecast for the user's current location.

I'm proud to announce that the StormWatch+ app has been re-released as version 3.0 with an entirely redesigned interface for displaying both local and national weather information! It features a brand new radar display that is fast, smooth, and stretches from coast to coast, PLUS includes overlays like storm tracks, watches/warnings, severe weather outlooks from the Storm Prediction Center, and even global (yes, global!) satellite. Zoom out from street level to a nationwide view instantly, drop in satellite imagery and storm tracks, then hit loop. Within seconds you'll have the national picture in a smooth animation!

Not only did we start from scratch on the graphics, but you can now get current conditions and the National Weather Service pinpoint forecast for anywhere in the nation (not just your current location) by entering a city, ST or zip code in the location box. And we don't use computer model data that changes hourly and can't be trusted past three days for our forecasts - no way! Ask any meteorologist and they'll tell you that models are for use in preparing a forecast, not the forecast itself! By using the NWS point forecasts, you get "human-powered" weather the way MWN has always delivered it.

In addition, if you have locations across the U.S. set in the alert settings screen, two taps will take you straight to the current conditions, forecast, and radar for those locations! In sum, StormWatch+ is now ready to compete with the "big boys" of the weather app world and their huge corporate backing. My goal is to see StormWatch+  become MANY people's go-to weather app in the coming months!

Now, I'm certainly not asking you to abandon your MWN app or the StormWatch+ alerting within it. There's no need to buy the alert feature in both apps (unless you want to program 6 locations for alerts!). However, if you want a free nationwide app to use for forecasts, radar, etc. while traveling, or just to check out the weather where grandma lives, I highly recommend you give StormWatch+ a try! It's free, why not?! Then, let us know how it compares to the "nationally-known" apps from household names we all recognize. We would love some great reviews in the App Store! Certainly you may send your suggestions directly to us and they will be considered for future releases.

And of course, if you have friends or family living somewhere other than the Memphis area, and they have an iPhone or iPad, tell them to download the StormWatch+ app from the App Store!  They'll get the proven reliability of our mobile weather alerting no matter where they are, as well as enjoy high fidelity, reliable weather information nationwide, backed by the same source you trust for Memphis weather.

Learn more about StormWatch+ and download it from our website: www.StormWatchPlus.com.

Erik Proseus
MWN Meteorologist

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First week of spring - snow, then warmer!

After weeks of above normal temperatures, spring officially begins with - what else - snow and Freeze Warnings! After an unusually warm winter, astronomists deem it spring and "the lost winter" shows up!

Today - cold and "snow"?

What may be the last gasp of winter arrives with accumulating snow on the northeastern seaboard and cold temperatures across the eastern U.S. An upper level low diving south across the region is responsible for our clouds and scattered showers this afternoon, while cold surface high pressure over the Plains and low pressure off the Atlantic coast combine to bring a gusty north wind and chilly temps to the Mid-South today.

A deep (strong) upper level low pressure system at 500mb (about 18,000') is located over northwest TN this afternoon, which is driving the formation of showers in the region. The degree of upper level "energy" is shown by the colors with strong values over the metro early this afternoon according to the GFS model.

Some of these showers are producing a mix of snow and graupel ("soft hail" or "snow pellets," or as I sometimes reference them as - "dippin dots"). Even though the temperatures at the surface are in the mid 40s to near 50, the freezing level is dropping below 2,000 feet and the temperatures at 5,000 feet are between 15-20° F. This is supportive of freezing precipitation aloft that simply doesn't have enough time to completely melt as it falls to the ground. All of this will end with sunset tonight and skies will clear.

Temperatures at about 2,500' are below freezing (blues) as shown by the GFS model valid at 1pm today. This is contributing to the mixed precipitation that is occurring at the surface. All precipitation at this level is snow.

Temperatures at 18,000' are very cold around the upper level low, approaching -35°C, according to the GFS model valid at mid-day.

Tonight - protect outdoor plants

High pressure moves east and will be over the Mid-South Monday, meaning a slightly warmer day, but a very cold start to spring break week for many school kids. Freeze Warnings and Frost Advisories warn of air cold enough to cause damage to some of the young plants that have started to grow already in the previously-mild March air. Many places in the outer suburbs of the metro - indeed much of the region outside the Memphis heat island and the MS/AR Delta - will see temperatures fall below freezing for a few hours early Monday morning. If you're worried about outdoor vegetation, tonight is a good night to offer them some protection from the cold with a blanket or other cover, or bring them in the garage or covered patio if possible.

Later this week - warming with a chance of thunder

By Tuesday, we'll be back in a more springlike pattern as wind turns southerly and becomes gusty and temperatures respond by climbing towards 70° under abundant sunshine. Wednesday will be similar with the morning chill a thing of the past and more clouds overhead as our next weather-maker approaches. Rain and probably some thunderstorms will be a good bet Thursday. The latest computer models that go out that far are making this system more "progressive," which means it moves through a little more quickly. In fact, most of the rain could be done by noon if the current model solutions are correct. That would limit the instability that comes with daytime heating this time of year so hopefully storms remain at bay.

StormWatch+ Re-Energized!

Tomorrow marks the roll-out of version 3.0 of our StormWatch+ national weather app. In work for several months, this version marks a significant improvement in the "front end" of the app, which admittedly had been lacking. While the severe weather push notification alerts are not being changed, pretty much everything else is. The result is what I am hoping will become a weather app of choice for nationwide use to get day-to-day, reliable weather information, including local radar, current conditions, and the general forecast.

We've gone to great things to ensure a beautiful, fast-loading, smooth radar display with precipitation typing and multiple layer selections that cover the entire nation, but also can be zoomed to your neighborhood (sorry, no screenshots ahead of tomorrow's release!). The forecasts are driven by the professionals at the National Weather Service, not a computer model that flip-flops 4 times a day or more. You know me - no crap apps here! NWS "point forecasts" are quality controlled by meteorologists in the the area that you request the forecast for.  In sum, we are hoping that StormWatch+ becomes #yourNEWweatherapp, especially for those outside the Memphis area, or for use by Mid-Southerners that travel and want a reliable app that will work nationwide.

StormWatch+ does not replace your MemphisWeather.net app for local use and you don't have to purchase StormWatch+ Alerts for push notifications from that app, as the MWN app has the same capability. However, it is free to download and removes the geographic boundaries that the MWN app applies. I hope many of our iPhone and iPad users will consider giving it a try! Unfortunately for Android users, it is currently only available for iOS, but we hope that its success will lead us to develop an Android version! You can download StormWatch+ here and then get the free upgrade to version 3.0 tomorrow when it is released. I think you'll like the great improvement you see! Check it out!

Erik Proseus
MWN Meteorologist

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Waterlogged Mid-South begins to dry out, and a little commentary

Recap of the past week

What an amazing weather week! The stage was set with daily record rainfall amounts on Wednesday and Thursday as nearly 8" of rain fell on the city, creating flash flooding scenarios, filling tributaries, and saturating the ground. That was followed by additional rounds of rainfall to end the week that dropped varying amounts, but exacerbated the flooding problem since all rain became runoff.

Estimated precipitation totals from March 8-10 courtesy NWS-Memphis.

The wet period ended late Sunday evening with a potent upper level system and accompanying surface low passing through the region, bringing a round of severe storms that promoted Tornado Warnings in the metro. Officially, the Memphis airport received 10.61" of rain since last Tuesday night, which puts March 2016 in 5th place for wettest March on record - and it's only the 14th. Another 1.25" is all that is needed to become the wettest March on record.

7-day rainfall amounts from the NWS show a swath of 10-12"+ amounts from northern Louisiana across southeast AR, and into the metro. Graphic courtesy WeatherBell.

The week ahead

Fortunately the next several days are looking much drier. Despite a couple of opportunities for light precip, no heavy rainfall is expected. In fact, we'll be back up to 80 degrees tomorrow with mostly sunny skies after a pleasantly sunny day today that saw temps in the 70s. Slight chances of rain will occur Tuesday night with a cold frontal passage and again Wednesday night as a weak system slides by to our south. A general cooling trend is expected as we head towards the weekend with rain chances returning late Friday into Saturday, but no heavy rain expected. Click here for the latest forecast from MWN.

NWS forecast for precipitation amounts over the next week. No heavy rain is expected, though a few passing systems could bring light amounts. This forecast subject to revision. Graphic courtesy WeatherBell.

Commentary

In the wake of this past weekend's weather, I have a few comments to make and I'll keep them brief.

• I'm PROUD and GRATEFUL for the contributions of my #TeamMWN interns, past and present. Several months ago, my wife and I registered for an out-of-town retreat for this past weekend. There was no changing it, and we had a great time. But somebody had to keep you all up to date! Enter current interns Patrick and Zeb and former interns William and Kevin, who were pulled "off the shelf." All four of them were in various stages of spring break and/or travel plans of their own, but all committed time to MWN to keep the home fires burning! You were in good hands and I was able to preserve my marriage! LOL. Outstanding work, gentlemen. Thank you!
• I returned in time to nowcast the evening severe weather event with Patrick. In case you weren't aware, we typically tag-team big events to make sure everything is covered and you all get the info you need. Fortunately, lingering effects of a weekend of flu-like symptoms (no really, how great is that?) didn't keep me out of the game! Despite some serious-looking storms, an amazing light show, and a bunch more unneeded rain, we are fortunate there wasn't more damage.
• Side note: if you put bullets 1 & 2 together, you'll know why I believe my wife is a saint. We got a planned weekend away, and she got stuck with a sick husband! Then I came home and worked a severe weather event. I love you honey! :-) 
• Enough of the mushy stuff... a couple of comments on last night's Tornado Warnings, particularly the Shelby County warning:

1. The storm that produced the warning had a history of producing a tornado, but had traveled over lightly-populated area as it approached the metro from the southwest. The National Weather Service had received no reports as the storm neared the metro despite a Tornado Warning being in effect and decent rotation being observed on radar. 
2. As it neared the southwest tip of the metro, the NWS opted for a Severe Thunderstorm Warning for northwest DeSoto County and the heart of Memphis and Shelby County as rotation had become fairly broad and there were no ground reports from the storm of damage. Shortly after issuing, an unconfirmed report of a funnel cloud was received in northwest DeSoto County.
3. In an abundance of caution and with broad rotation, but no "tornadic signature," evident on radar, a Tornado Warning was issued for Southaven and much of the southern and central sections of Shelby County, including Memphis. With a storm that had a history of "nefarious behavior," a possible funnel reported, and a highly-populated area ahead of it - after dark - that was absolutely the right call. You simply can't make a mistake the other direction and not warn the public. Once the storm had traveled over some of that population center and no reports were received of damage, as well as the storm becoming less organized, it was also a good call to cancel the Tornado Warning early.
4. Sirens... We had a "YUGE" (as Trump would say) number of questions on their sounding or not sounding when people thought they should/shouldn't. I've discussed the purpose of sirens before and regular readers and followers know you shouldn't count on them, especially indoors at night with pouring rain and wind. They are for outdoor use only. I'll make two points on their use. First, depending on where you live, the siren activation policy is different, even across Shelby County. Memphis and Shelby County (outside of Bartlett, Collierville and Germantown) currently sound for their entire area of responsibility if any part of Shelby County is under a warning. Bartlett, Collierville, and Germantown sound them if any part of their individual municipality is affected. Memphis was pursuing a more targeted siren policy some time ago, but so far that has not transpired. Second, the sirens are manually activated by the authorities in the respective jurisdictions, not by the NWS. That means that they are also DE-ACTIVATED manually. Sometimes it takes several minutes, especially if a warning is cancelled early, for that jurisdiction to shut down their sirens. It's not surprising then that sirens will still be sounding for a bit after a warning is cancelled.  Thirdly, in general, many of the sirens will wail for a couple of minutes, stop for a couple minutes, then start back up again. This is because they use mechanical motors and running them for 30-60 minutes straight burns the motors up. To keep their lifespan high, the cycling is necessary. We have an Outdoor Siren Page on MWN that you may wish to visit.

Erik Proseus
MWN Meteorologist

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Rainy pattern is here to stay - how long and how much?

7pm UPDATE

Flash Flood Warnings have been extended further east and now include areas near the Mississippi River on the TN/MS side (red boxes in the graphic below). A stationary front is oriented just east of where the Flash Flood Watches are in effect (green shaded counties) with the axis of heaviest rainfall just west of that front.

Models have insisted that the front would pull back to the west tonight, moving the heavy rain axis west of the metro with it. However, with all of the rain along the river, this "cooled" air is effectively keeping the front to our east. As long as it stays east, we'll remain under the conveyor with waves of heavy rain and thunderstorms.

The latest high-resolution model data (HRRR model) now thinks the front could move back to about Memphis by rush hour tomorrow. If that is correct, then periods of heavy rain will continue overnight. The HRRR model prints out overnight rainfall totals ranging up to 4-5" west of the river to less than an inch on the far eastern side of the metro (below).

Predicted rainfall totals for the overnight hours (through 6am Thursday) from the high-resolution HRRR model. Graphic courtesy WxBell.

If these totals are realized, significant flooding issues could result, especially in urban areas, and creeks and streams will overflow their banks. The Loosahatchie River is already predicted to crest above flood stage tomorrow. Additional rainfall will only exacerbate these types of issues.

FLASH FLOODING OVERNIGHT IS ESPECIALLY DANGEROUS. It is very hard to see how deep water is (or even see that you are about to drive through low-lying flooding or pooling on roadways). Nearly half of all flooding deaths occur in vehicles. Remember - turn around, don't drown!

UPDATE 7:20pm
The Flash Flood Watch has been extended east to include the rest of the metro (shaded green counties).

In addition, the NWS Weather Prediction Center is monitoring our area for flooding as the "warm conveyor belt" continues to affect the same areas. There is concern that it will move very little overnight in the metro.

ORIGINAL POST (1:30pm)

There's really no much more that needs to be said, but there's a lot that can be said. I'll try and split the difference.

Weather systems like this, in which fronts stall, low level jet streams are active, abundant moisture is shooting out of the tropics like a firehose, and waves of upper level energy pulse through the region, are very difficult to predict where the heaviest will fall. Last weekend, we warned of perhaps half a foot of rain, especially in east AR. Forecast totals in the metro dropped early in the week as it looked like the heaviest would remain west of the local area.

Within the past 24-36 hours, those forecast totals are starting to climb again. The rainfall forecast from the NWS Weather Prediction Center from 6am this morning through 6pm Saturday aare shown below with generally mentioned amounts of 3-5" possible for the metro. However, you'll need to add the inch and a half received overnight to that! So far this morning, the airport has received nearly an inch more.

NWS Weather Prediction Center rainfall forecast from 6am Wednesday through 6pm Saturday.

As of 1pm, a Flash Flood Watch has been issued for most of the metro, except Fayette and Marshall Counties, and all areas west of the river (green shaded counties below). Flash Flood Warnings are also in effect west of the river (red boxes in the graphic below). The lighter green irregular-shaped areas are river Flood Warnings, which includes the Loosahatchie River in the metro.

As of now, we're expecting another round of steady, occasionally heavy, rain and some thunderstorms later this afternoon through the evening hours. There are some indications that  the axis of heavy rain will shift from the Mississippi River area westward overnight. However, another wave of rain will move in tomorrow with thunderstorms again possible. Thursday is likely to be the heaviest rain with this system here in the metro. The area is outlooked within a moderate risk of rainfall exceeding flash flood guidance, meaning there is a 10-15% chance that more rain will fall than the ground can handle and flash flooding will ensue.

The Excessive Rainfall Outlook for Wednesday indicates a large area in the Lower Mississippi Valley  west into eastern TX that will be prone to flash flooding. A Moderate Risk exists from the Memphis area southwest into the MS Delta.

By Friday, the overall upper level pattern begins to shift as a low over deep south TX/northern Mexico - which is ultimately responsible for this pattern - moves towards the Mid-South and a front moves to our east. That will mean less very heavy and steady rain over the same areas, but continued elevated rain and thunderstorm chances into Friday and Saturday as the low moves into the region. Driven more by daytime heating, rain and thunder chances should be highest in the afternoon and evening time frame as we head into the weekend. One last round of potential thunderstorms arrives late Sunday as an upper level low moves overhead with dry and very warm weather expected to start next week.

So, for the next few days, we strongly recommend avoiding driving into or through areas known to hold water or flood in heavy rain; if you come across these areas, avoid them - turn around don't drown; and be sure your street gutters and other areas where water flows around your home are free of debris. If you are typically affected in some way by rising water during heavy rain, expect those problems again and prepare now.

Follow our social channels for the latest information and be sure to get the MWN mobile app for current radar loop, forecast, and Flash Flood Warnings delivered via StormWatch+!

Erik Proseus
MWN Meteorologist

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Does Lowe's sell gopherwood? Flooding rain potential this week

A gorgeous weekend is in the books as high temperatures reached 70 degrees both Saturday and Sunday with a good deal of sunshine. Warm weather is here to stay, but the sunshine will be replaced by clouds, increasing wind, and, by mid-week, rain measured in inches.

Starting the week off, dry and warm conditions are expected Monday and most of Tuesday as high pressure off the Atlantic coast brings in warm southerly wind and a storm system out west begins to set up. This will mean occasionally gusty wind and above average temperatures with highs in the lower 70s and lows in the 55-60° range.

To our west, an unusually deep (strong) upper level low pressure system will eventually "cut off" from the main air flow across the country and sink south into Mexico, where it will "sit and spin" for a couple of days (see first graphic below). At the same time, the jet stream level wind, which typically blows west to east across the nation will buckle. It's common for ridges and valleys to form in the jet stream, but in this case a valley will become a cliff! As the wind moves into the western U.S., it will dive south around the anomalously low pressure in Mexico, then shoot back to the north over the Southern Plains (see second graphic below).

Anomalies, represented as standard deviations, in the upper level pressure pattern (18,000') on Wednesday morning. Unusually low pressure over Mexico (6 standard deviations below normal) will feed abundant tropical moisture north on the eastern side of the low into the south-central U.S. and eventually the Mid-South. Graphic courtesy WxBell.

The jetstream pattern on Wednesday morning is also highly unusual pattern with a low pressure area over northern Mexico and "meridional flow" (north-south, rather than west-east) over the center of the country. The jet stream from the south will transport record-breaking atmospheric moisture north into the eastern Plains, shifting east towards the Mid-South later in the week. Graphic courtesy WxBell.

The graphics above are effective Wednesday morning, but the general pattern will remain in place for a couple of days, meaning that whatever weather pattern they create at the surface will be stagnant. Unfortunately, that pattern for the south-central U.S. into the lower Mississippi and Ohio Valleys will be a wet one. The upper low over Mexico will serve to pull abundant amounts of atmospheric moisture north, transported by the south-to-north jet stream. Under the jet stream, and with possibly record-breaking amount of moisture in place, rainfall will be heavy and persistent, leading to flooding concerns across LA, AR, and southern MO Wednesday, and periods of heavy rain in the metro by Thursday. Bouts of severe storms are also possible the first half of the week, mainly southwest of the Mid-South.

Atmospheric moisture is depicted using precipitable water values (PWAT) for Wednesday morning. An "atmospheric river" of moisture that leads from the tropics into the central U.S. will feed tremendous rainfall amounts under it's core. Due to it's location, this atmospheric river has been dubbed the "Mayan Express" (similar to the "Pineapple Express," which feeds moisture from the central Pacific near Hawaii into California during periods of heavy rain there). Graphic courtesy WxBell.

By late in the week, the upper low over Mexico will finally start to move, but it will head northeast across eastern TX into AR and the Mid-South. This means that even though the flooding threat should diminish, an unsettled pattern will remain in place for the metro with periods of showers and thunderstorms all the way into next weekend. 

Rain chances will generally drop a bit each day after Thursday, but we'll still be dealing with decent chances of rain and thunder each day through next Saturday, and possibly Sunday. It also means that we'll remain in a warm pattern with highs remaining near 70° and lows in the upper 50s or warmer as surface moisture levels (dewpoints) remain high. Rainfall totals this week could be over a foot in parts of LA, 8-10" north into central AR, and a very large area of 3-5" totals, including the metro. 

Forecast rainfall totals through next Sunday morning from the NWS. Totals above 5" are evident west of the Mississippi River, which 3-5" is expected in the metro. Graphic courtesy WxBell.

Areas that typically experience high water with heavy rain will likely see that occur this week, especially on Thursday and possibly into Friday. In addition, Mississippi River water levels are already running higher than normal. With excessive rainfall upstream from the Mid-South, I expect those with interests tied to the river will need to continue to monitor water levels through March.

Stay tuned for later forecasts and be prepared for possible flooding late this week. We'll have daily updates either on this blog or our social media feeds listed below.

Erik Proseus
MWN Meteorologist

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February 2016 Climate Data and Forecast Accuracy

February Recap

After a very warm start to the winter, then an "average" January, February was back into the warmth with temperatures that averaged over 2.5° above normal. February precipitation was also wetter than average after a drier January, though no winter precipitation occurred during the month. Three days had precipitation totals over 1.5" with spotty flash flooding occurring on the 2nd. No severe weather occurred during the month. The end of February also marked the end of meteorological winter with temperatures averaging much above normal and precipitation slightly below normal.

Winter Recap

With Leap Day in the rearview mirror, it brings us to the end of meteorological winter, defined as December-February. The winter of 2015-'16 ended up very warm with slightly below normal rainfall and well below normal snowfall (at least at the official recording station at Memphis International Airport). Temperatures averaged 47.8°, which was 4.4° above the long-term average and 7th warmest on record dating back to 1875. Precipitation totaled 12.62", which was 1.49" below average. Snowfall was just 0.3" at the airport (though 3"+ occurred not far north in Tipton County). Normal snowfall in Memphis is 3.4", so this winter was 91% below normal. 

Memphis International Airport, Memphis, TN

Temperature
Average temperature: 48.1 degrees (2.6 degrees above average)
Average high temperature: 57.3 degrees (2.6 degrees above average)
Average low temperature: 38.9 degrees (2.6 degrees above average)
Warmest temperature: 75 degrees (2nd)
Coolest temperature: 24 degrees (10th)
Records set or tied: Record high set on February 2nd (75°).
Comments: Five days reached 70° or higher in February.

Precipitation
Monthly total: 5.58" (1.19" above average)
Days with measurable precipitation: 9 (0.2 days below normal)
Wettest 24-hour period: 1.76" (14th-15th)
Total Snowfall: None
Records set or tied: None
Comments: Three days recorded more than 1.50" of rain.

Miscellaneous
Peak wind: Northwest/45 mph (25th)
Average wind: 9.0 mph
Average relative humidity: N/A
Average sky cover: N/A

Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature
Average temperature: 46.4 degrees
Average high temperature: 57.1 degrees
Average low temperature: 36.6 degrees
Warmest temperature: 74.0 degrees (2nd)
Coolest temperature: 19.9 degrees (10th)
Comments: None.

Precipitation
Monthly total: 5.07" (automated rain gauge), 5.48" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 9
Wettest date: 1.82" (23rd) (via automated gauge)
Total Snowfall: None
Comments: None

Miscellaneous
Peak wind: 27 mph (19th)
Average relative humidity: 70%

Click here for a daily statistical recap for Bartlett, TN.

MWN Forecast Accuracy

MWN average temperature error: 2.47 degrees
MWN forecast temperatures within 2 degrees of actual: 57%
MWN average dewpoint error: 2.77 degrees
MWN forecast dewpoints within 2 degrees of actual: 58%

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours). Historical accuracy statistics can be found here.

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