MWN Blog: March 2021

Friday, March 26, 2021

Details on yet more severe weather chances this weekend

With two major severe weather events in the past 10 days leaving the immediate metro virtually unscathed, we'll have to hold out hope that we can do it one more time this weekend - which is hard to believe given the awesome spring conditions we have today!

Saturday

Enjoy the gorgeous conditions today, as we'll be hearing thunder by the time most of us wake up Saturday morning, thus commencing a possibly busy 24 hours. A warm front will move across north MS overnight with scattered showers and thunderstorms developing along it as it nears the metro in the early morning hours. I expect we'll be hearing that thunder after about 5am tomorrow. We are in a Marginal Risk (level 1/5) for a few hail storms in this initial batch that will continue through the morning hours as the front pauses roughly along the state line.

A Marginal Risk of a few hail storms exists Saturday morning. The graphic above (labeled Friday) is valid through 7am Saturday. (SPC)

The biggest question mark for tomorrow seems to be how far north that warm front will lift, and our best high-resolution models do not agree. The HRRR model from this morning indicates it gets not much further north than the I-40 corridor, keeping the Memphis area in a rainy pattern much of the day. The NAM3 model, on the other hand, lifts it into northeast AR and northwest TN, resulting in a decrease in rain trends by midday into the afternoon.

The two images above are from the Friday morning runs of the HRRR model (top) and NAM3 model (bottom) both valid at noon Saturday. Clearly they have different opinions of how the day will turn out, thus a lower than preferred confidence on tomorrow's forecast. (WxBell)

While I do believe rain chances diminish during the afternoon from the morning hours, like the NAM3 model shows, I don't necessarily believe the front will move too far north of I-40. So chances of rain likely continue throughout the day, though highest during the morning hours versus the afternoon. In addition to the morning hail threat, with showers and thunderstorms (even if scattered) over the general area, a minor flash flooding concern will develop as well. If the HRRR model verifies, rainfall will be a larger threat along the I-40 corridor from repeated storms during the day. Rain totals will be monitored as most areas are saturated from recent rainfall.

Saturday night

A greater risk of severe weather seems to be developing Saturday night. Once again, timing is a bit difficult due to the challenge of identifying where the warm front will be to start the evening. However, thunderstorm activity will ramp up overnight as a cold front sweeps in from the northwest and takes over the airspace from the warm front lingering in the region.

The surface weather map valid Saturday evening. A warm front is just to our north while a cold front is seen to our northwest poised to sweep through overnight. (NWS)

With wind at all levels fairly strong and instability present, especially in the evening, storms that develop could be strong to severe. While damaging wind is the primary concern, some hail is possible, and a tornado or two cannot be ruled out. Below is the Friday morning severe weather outlook for Saturday through Saturday night. The I-40 corridor is in the heart of a level 3 (Enhanced Risk) area. We'll need to watch this carefully, particularly how much instability can develop during the day (which would be enhanced by drier conditions and a bit of sunshine during the afternoon) and where the warm front ends up.

The severe weather outlook for Saturday into Saturday night indicates an Enhanced Risk (level 3/5) of severe storms, mainly after dark Saturday night. The tornado risk (upper right) is around 10% along the I-40 corridor as of Friday morning. That is the probability of a tornado within 25 miles. The hail and strong wind threats are at 15% each (bottom two panels). (SPC via Pivotal Weather)

While the chance for severe weather is present, most likely to occur will be a well-organized area, or line, of storms along the cold front. That is likely late in the night, possibly as late as the pre-dawn hours Sunday morning. Once again, heavy rain will be expected. The flash flooding or urban flooding risk goes up a notch Saturday night.

The Weather Prediction Center places the areas along and ahead of the front in a Slight Risk for excessive rainfall that could lead to flash flooding - or 10-20% chance. I firmly believe by Sunday morning we'll all be tired of rain and some of us may have some water damage with 4-6" of rainfall in total over the previous 5 days or so.

A Slight Risk (10-15% chance) of excessive rainfall is predicted for a large swath Saturday into Saturday night. (WPC via PivotalWeather)

Once all of the storms move out by Sunday morning, a calmer patter will prevail for a few days. The next big front arrives mid-week. Severe weather chances appear lower right now for this system but it will bring us a period of much cooler weather to end next week.

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

Sunday, March 21, 2021

First official week of spring: more storms in the forecast

Welcome officially to spring! The vernal (spring) equinox occurred at 4:37am Saturday. While the weather felt more like spring to start the week last week, the mid-week severe weather threat and cold front brought in a chilly and cloudy pattern to end the week. This weekend is starting to feel a bit more like spring though, despite chilly mornings. Sunshine has pushed afternoon temps into the upper 60s as the sun stays awake a little longer in the evenings!

We've got one more day of dry weather to start the week, despite cloud cover Monday, with highs back near 70 once again. Then the weather pattern becomes a bit more inclement again for the middle portion of the week. As moisture from the south streams in, upper level systems move out of the southwest U.S. and across the southern states before turning northeast into the Mid-Mississippi Valley. That will put the Mid-South in a favorable position for thunderstorms as the surface lows move by to our northwest.

Precipitable water values on Tuesday morning indicate high moisture content streaming up the Mississippi River Valley. Rain is likely; storms are a question mark. (WxBell)

The first of those systems affects the area on Tuesday. Rain chances increase late Monday night before rain becomes likely on Tuesday. A few thunderstorms are also possible, though this system will be weakening as it approaches, so severe weather will be unlikely. Most rain will be gone by early afternoon though a few showers could stick around in the afternoon as temperatures top out near 70 once again. It will also be a windy day with south wind gusting to 25-30 mph.

The European model showing CAPE (i.e. unstable air) for Tuesday. CAPE values are meager and don't lend themselves to potent storms, though some thunder is certainly possible. (WxBell)

The cold front will stall out just to our south Tuesday night and Wednesday, leaving mild conditions and mainly dry weather. It will be a bit warmer with highs in the mid 70s and partial sunshine Wednesday.

By Wednesday night, the next system will be moving across the southern U.S. and it appears to be a bit more potent. Warm, muggy, and very moist air air will overspread the region on strong southerly wind ahead of the approaching surface low and upper level energy. This system bears watching closer as we could be dealing with severe weather again if certain model solutions pan out and all ingredients come together. At the very least, heavy rain appears likely.

CAPE value for Thursday are much more robust according to the European model, so "storm fuel" should be sufficient for severe weather should all other ingredients come together. (WxBell)

The discrepancies between the models are starting to iron themselves out and likely will further Monday into Tuesday when we'll have a better idea of what to expect. For now, keep your weather antenna up for Thursday, just as we did ahead of last Wednesday. All modes of severe weather could be possible during the daytime hours as highs reach into the 70s - so remain weather aware!

Fortunately, the system is progressive and appears to be on its way out by Thursday night, leaving mild weather in its wake to end the week and start next weekend. Rain chances could start moving back in by about a week from today if long-range solutions are right.


MWN is a NOAA Weather Ready Nation Ambassador	Meteorologist Erik Proseus is an NWA Digital Seal Holder

Saturday, March 13, 2021

Spring has arrived - and so have severe weather chances

Spring has sprung across the Mid-South! Temperatures have warmed considerably from a month ago and meteorologists have shifted the mindset from looking for snow in the extended forecast to watching for severe weather chances.

A recent spell of highs in the 70s has been the lengthiest such streak in four months, welcome news for those that grew weary of counting the days until we got back above freezing! This weekend we'll be dealing with a series of fronts that will bring rounds of precipitation to the area.

This weekend

This (Saturday) morning, a cool front has slipped to our south. Post-frontal showers are moving east over northern AR and west TN this morning, bringing some rain to portions of the metro. With upper level energy departing, rain chances drop this afternoon to the "chance" category with most areas dry as high temperatures climb through the 60s. A northeast wind and lingering clouds may be enough to stop our 70-degree streak at five unless we can eek out an extra degree or two today.

Tonight, the front starts to lift north a bit and a stray shower or two are possible, otherwise it'll be mild with temperatures only falling to the upper 50s. There will be one less hour for temperatures to drop tonight, as we press our clocks forward into Daylight Saving Time! Don't forget to check your batteries in smoke detectors and weather radios as well!

Sunday starts cloudy, obscuring the delayed sunrise that occurs at 7:12am. However, the front in Mississippi lifts to our north, wind shifts to the southeast, and temperatures respond accordingly, rising back into the mid 70s. The huge storm system to our west - the one responsible for all the snow in Colorado and Wyoming and severe weather in the southern plains today - moves in our direction as well. A couple of daytime showers are possible Sunday, but most precipitation holds off until overnight. A bonus: daylight lingers past 7pm!

A very busy weather map for Sunday with snow and freezing precipitation in the west and north, rain and thunderstorms in the south. (NOAA/WPC)

Sunday night

On Sunday night, that storm system to our west approaches, but in a weakening state. Rain becomes likely overnight, particularly after midnight, with some thunderstorms also possible. The Storm Prediction Center (SPC) currently has areas from Memphis southwest into the Delta highlighted for a Slight Risk (level 2) of severe weather and the rest of the region in a Marginal (level 1) Risk. The contributors to this risk are strong wind (particularly aloft) and wind shear. The main limiting factor is a lack of unstable air. I'd be more worried if it were arriving in the mid to late afternoon.

The severe weather outlook for Sunday includes a Slight Risk (level 2/5) for yellow areas in the upper left, including the city of Memphis. The primary risk is strong wind (lower right - 5-15% within 25 miles), while a small risk of a tornado exists as well (upper right - 2-5% chance). (SPC via Pivotal Weather)

A few storms could bring strong wind gusts, mainly between midnight and 6am. An isolated tornado can't be ruled out due to the wind shear, but chances appear fairly slim. Heavy rain is also expected in possible bands or a line overnight.

Early next week

By Monday morning, the system will be pushing east and sunshine will break out across the region. With the front's origins in the Pacific rather than Canada, mild weather follows with highs back into the mid 70s and a decent breeze. It'll be a great spring day! Tuesday will be similar temperature wise, although high clouds will be streaming overhead in advance of the next weather-maker.

Wednesday - severe storms?

That next system, a more potent low pressure center moving by to our north and cold front poised to slice through the Mid-South, arrives Wednesday. Timing is still a bit uncertain, as are the details on the low track and potential instability, but we'll be watching this one closely. SPC has already highlighted a large area, including the metro, for a risk of severe weather. Given the likely daytime arrival, we'll have more warm air to work with. Upper and mid-level dynamics look favorable for severe weather as well. We'll have more on it, but stay weather aware on Wednesday and be prepared to adjust plans as necessary.

Another, likely more potent, risk of severe storms exists on Wednesday, as shown by SPC above, for a much larger area than Sunday. Details are still TBD. (Pivotal Weather)

Late next week

Drier weather settles in behind Wednesday's departing system with cooler temperatures as well. There is a chance we could see a couple showers Thursday if the upper level low associated with Wednesday's system moves overhead, but skies clear heading into the weekend with slightly below average temperatures that moderate with time.

So, to summarize - minimal severe weather chances Sunday night, the potential for more impactful severe storms on Wednesday, and change your clocks tonight! Happy Spring!


MWN is a NOAA Weather Ready Nation Ambassador	Meteorologist Erik Proseus is an NWA Digital Seal Holder

Saturday, March 6, 2021

February 2021 Climate Report for Memphis, TN

February Climate Recap

February will definitely be one of the winter months that Memphis won't soon forget, as well as one for the record books. A long-duration extreme cold snap enveloped the entire central portion of the country as far south as the Mexican border for the middle third of the month, breaking records (and pipes and electric grids)! With an average temperature of 37 degrees, it was the tenth coldest February on record in Memphis, but also the second snowiest as 10" of snow and sleet fell between the 14th and 17th. And that followed about one-third of an inch of ice on the 11th. In sum, Memphis officially remained below freezing for nine consecutive days, tying the longest stretch below freezing on record.

The month began a bit below normal as well, but many people will forget the way the month ended. Four days after climbing above freezing, it was nearly 70 degrees, and the maximum temperature for the month was 75degrees on the last day of February. In addition, soaking rains and some thunderstorms (that occurred with a Tornado Watch in effect) brought 5" of rainfall in the last 3 days of the month, bleeding over into the early morning hours of March 1. Snowmelt and heavy rain meant saturated conditions heading into the first days of meteorological spring.

As for severe (non-winter) weather, storms on the evening of the 28th brought sub-severe hail and wind gusts measured to 67 mph with some wind damage, including a tree down on a house that resulted in one injury in Midtown Memphis. There was also some minor flooding in Tipton County that night. A Tornado Watch was in effect and Severe Thunderstorm Warnings were issued, as well as a Tornado Warning for southern Marshall County.

Memphis International Airport, Memphis, TN

Temperature

Average temperature: 37.0 degrees (8.5 degrees below average)

Average high temperature: 44.6 degrees (10.1 degrees below average)

Average low temperature: 29.5 degrees (6.8 degrees below average)

Warmest temperature: 75 degrees (28th)

Coolest temperature: 1 degree (16th)

Heating Degrees Days: 778 (230 above average)

Cooling Degree Days: 2 (0 below average)

Records set or tied: The following temperature records were set or tied during the month:

Coldest high temperature: February 14 (19°)
Coldest low temperature: February 15 (9°)
Coldest high temperature: February 15 (15°)
Coldest low temperatures: February 16 (1°)
Tied coldest high temperature: February 16 (18°)
Coldest low temperature: February 20 (9°)
Tied for consecutive days with high temperatures at or below 32° (February 11-19)

Comments: 16 dates recorded low temperatures at or below freezing versus an average of 9.5. Nine (consecutive) days recorded high temperatures at or below freezing versus an average of 0.9. The average temperature for the month ended 10th coldest in the 147 year historical record.

Precipitation

Monthly total: 6.95" (2.56" above average)

Days with measurable precipitation: 14 (4.8 days above average)

Wettest 24-hour period: 2.26" (26th-27th)

Snowfall: 10.0" (8.7" above average)

Records set or tied: Two daily snow records were set this week: 4.0" (sleet and snow) on the 15th and 4.7" on the 17th.

Comments: Snow fell on six (consecutive) days during the month, including the two record above, as well as 1.3" on the 14th and trace amounts on the 13th, 16th, and 18th. This month ranks second snowiest on record behind 10.3" that fell in 1905. In addition to the snow, two days also recorded more than an inch of rain.

Miscellaneous

Peak wind: West-northwest/42 mph (25th)

Average wind: 8.7 mph

Average relative humidity: 67%

Average sky cover: 67%

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature

Average temperature: 36.4 degrees

Average high temperature: 44.4 degrees

Average low temperature: 28.2 degrees

Warmest temperature: 75.6 degrees (28th)

Coolest temperature: -0.3 degrees (16th)

Comments: None

Precipitation

Monthly total: 7.12" (automated rain gauge), 7.37"(manual CoCoRaHS rain gauge)

Days with measurable precipitation: 13

Wettest date: 2.16" (28th) (via automated gauge)

Snowfall: 8.6"

Comments:

Miscellaneous

Peak wind: South/26 mph (21st)

Average relative humidity: 79%

Average barometric pressure: 30.14in. Hg

Comments: None

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

MWN Forecast Accuracy

MWN average temperature error: 3.31 degrees

MWN forecast temperatures within 2 degrees of actual: 45%

MWN average dewpoint error: 3.08 degrees

MWN forecast dewpoints within 2 degrees of actual: 48%

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

Climate Outlook - March 2021

The March climate outlook for the United States from the Climate Prediction Center is shown below. Above average temperatures are forecast for a large section of the United States with highest probabilities in the Great Lakes and Southern Plains to Gulf Coast. Below average temperatures are forecast for the west coast. Odds favor above average temperatures for Memphis (48%) versus only 19% chance of below average temperatures. The average temperature for March is 54.0 degrees.

Precipitation is expected to be above normal from the Great Lakes into the Ohio and Tennessee Valleys. Below average precipitation is forecast for the southern Rockies into the Four Corners during March. For Memphis, odds favor above average rainfall (a 45% chance) versus only a 22% chance of below average rainfall. Precipitation historically averages 5.16 inches.

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Follow MWN on Facebook and Twitter for routine updates and the latest info!

Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app

Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!


MWN is a NOAA Weather Ready Nation Ambassador	Meteorologist Erik Proseus is an NWA Digital Seal Holder

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