Sunday, March 26, 2017

Get used to it... another severe weather threat

We've moved into a particularly active weather pattern in the Mid-South with the effects of one low pressure system on Saturday now having departed and another making it's way towards the area on Monday. There are probably two more in the next week or so after Monday, so remain vigilant in checking for the latest details as each system approaches.


Monday severe weather threats

Specifically for tomorrow, low pressure will move by to our north during the afternoon and evening tomorrow, dragging a cold front through during the early evening hours. This low has ignited the first "chaser convergence" scenario of the spring out in Oklahoma and north Texas where the threat of severe storms is much higher this afternoon.

The surface map from 7pm Sunday to 7pm Monday in 6-hour steps shows low pressure moving out of the Plains across southern MO and into the Lower Ohio Valley, dragging a front into the Mid-South. (NOAA)
As the low moves across southern Missouri later tonight, a few showers will be possible early Monday morning locally but these should be of little consequence. However, as we get farther into the day, instability levels will rise as brisk south wind ushers in warm, moist air from the Gulf and temperatures rise into the 70s by lunchtime.

With cold air aloft associated with the low and warm air below, scattered thunderstorms will develop sometime around mid-day and continue through the afternoon hours. One final push along the front, with perhaps a little more organized line of storms, will occur early in the evening, ending the threat for the day.

The high-resolution NAM model simulated radar from about 1am tonight through 1am Tuesday shows an overnight line of storms dissipating before arriving tomorrow morning ,then additional scattered showers and thunderstorms forming in the heat of the day and moving through during the afternoon and early evening hours. (Pivotal Weather) 
That cold air aloft will create a scenario with high lapse rates, which means the temperature drops faster than normal as you go up into the mid levels of the atmosphere. Higher lapse rates, when combined with sufficiently unstable air, creates a scenario in which hail can form. Thus, large hail and high wind will be our primary threats tomorrow.

With afternoon surface wind out of the southwest, low-level shear will be minimized a bit and the tornado threat will be non-zero, but low. We also expect these storms to produce dangerous lightning and the possibility of localized ponding of water or flash flooding due to the recent rains that have the ground already pretty well soaked. The graphic below summarizes the threats and timing.



Follow MWN on social media for later updates and download our mobile app for the current forecast, radar, social media feeds, and severe weather notifications when you activate StormWatch+. It'll let you know when severe weather is expected at your precise location(s). All links are provided below.

After Monday

Looking ahead, we'll have a respite for about 48 hours with decent spring weather Tuesday and most of Wednesday before the next system to our west makes a run at the Mid-South on Thursday, bringing yet another round of storms with the potential for some severe weather. Beyond that, Friday and Saturday look good with more storms on Sunday. It's like watching Groundhog Day...


Despite March arriving like a lion, it appears March may also go out like a lion! No rest for the weather-weary. Stay safe!

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

Friday, March 24, 2017

Severe weather threat on Saturday

Severe weather season appears to be starting as the Mid-South enters what looks to be a busy couple of weeks in the thunderstorm department!As always we take them one by one, and the first hazards appear tomorrow. Unfortunately, this doesn't appear to be a one-round match, but a multi-pronged attack.

A strong low pressure system over the Plains will slowly move northeast into the middle Mississippi Valley over the next 24-36 hours. Ahead of it, gusty southerly wind is drawing up warm, moist air from an abnormally warm Gulf of Mexico into the region. A cold front will take it's time moving across the lower Mississippi Valley on Saturday as the low anchoring it's north side weakens and slows down. This will set the stage for the potential for multiple rounds of thunderstorms, most in the form of lines or clusters, to move across the metro. This complicates trying to "time" the impacts.

The first is a little more clear than the others and looks to march across Arkansas overnight, arriving along the Mississippi River in the wee hours of Saturday morning, likely between 2-4am as we see it now (early afternoon Friday). The line will encounter a slightly less unstable airmass as it reaches east Arkansas, but could still bring the threat of damaging wind, perhaps some hail, and an isolated brief tornado, as well as dangerous lightning and heavy downpours. The Storm Prediction Center divides their outlook periods by day ending at 7am CDT. So, through 7am Saturday, the western metro is in a Slight Risk (category 2 of 5) and the eastern metro in a Marginal Risk (category 1 of 5) for severe storms (see left panel of graphic below).


Following the early morning round, which will likely be gone by the time many of you wake up on a typical Saturday, the metro will remain under an unstable airmass which could produce additional scattered showers and thunderstorms during the mid-morning hours. Strong south wind will continue to bring unstable air north and, as the front approaches, storms are expected to re-generate during the late morning and afternoon hours.

Timing these will be very difficult until they pop up on radar, so simply be prepared for the possibility of rain and storms just about anytime Saturday. The cold front finally moves through sometime in the late afternoon hours, ending the storm threat. The front could also be accompanied by strong storms, though it's more likely that if a squall line forms it will be just east of the metro (again, making timing difficult).

The SPC severe weather outlook for Saturday during the day (right panel in the graphic above) places east AR under a Marginal Risk (1/5) and west TN and north MS in a Slight Risk (2/5). Late morning and afternoon storm threats include primarily damaging wind, lightning, flash flooding in areas that get multiple storms, small hail and a low threat of tornadoes.

Sunday looks to be a warm, pleasant day then another round of storms is expected on Monday (potentially any time on Monday) with severe weather again possible. More on that later this weekend.

I'll wrap this up with an animation of the mid-level pressure/wind pattern for the next 10 days (through Sunday March 26) below. You'll notice that there are multiple "waves" of pink/red that move across the southern U.S. (at least 4 of them) during that 10 day window, all indicating the likelihood of a round of storms and any capable of producing severe weather somewhere along their track. It's spring and an active pattern has set up. It'll pay to stay close to your favorite weather sources and always have the latest information on the next storm system, as that information will change or be refined as each storm approaches.

Wind/pressure pattern at 18,000' (500 mb) over the CONUS through March 26, showing multiple "waves" of  weather moving across the Mid-South, each capable of producing storms, a few strong to severe. Click here if the loop doesn't animate. Graphic courtesy PivotalWx. 
Get the latest information from MWN at the links below, including our social media feeds, website, this blog, and our mobile apps. Here's the current forecast, generated by a real meteorologist (me) and not a computer. StormWatch+ should be your friend as we enter our primary severe weather season! Stay safe!

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
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

Sunday, March 19, 2017

Spring officially arrives with spring-like weather!


I go on vacation for a week and winter comes back! (Seriously, big ups to #TeamMWN interns for the awesome job holding down the fort this past week while I got some much-needed vacation time with the fam!) Now that I have things back under control (hehe)...

The vernal equinox occurs Monday morning at 5:29am CDT, and not a moment too soon! Monday should also be our first day this year in which everyone gets to 80° or higher. And all the people said...


Tuesday will be a reprise of Monday, though a front dropping into the northern sections of the Mid-South will mean a few storms for those close to the TN/KY border, a few of which could be strong as a large (cool) high pressure area pushes on the front from the north. Look for more low 80s and likely dry weather in the metro.


The cold front will drop south into the I-40 corridor Tuesday night and push to our south by Wednesday, bringing some of that cooler air to the north into the region with it. The dynamics of the system will have weakened and, with little upper support, scattered showers are the worst we can expect Tuesday night and perhaps early Wednesday. However, temperatures will be about 20° cooler Wednesday with lingering clouds and a north breeze. Highs will be in the lower 60s.

The NWS surface map for Tuesday evening shows an east-west front laid out across the Mid-South with cooler Canadian-based air behind it pushing slowly south into Wednesday. This will lead to scattered showers and a cooler day on Wednesday locally. (Hey, I can't use all GIFs and retain any credibility, right??) (NOAA/WPC)
Thursday should be a nice "in-between day as the front returns north with nary a peep. It'll allow wind to return to the south which should help push those temperatures back into the 70° range, making for a downright pleasant day. That wind gets stronger heading into Thursday night and Friday as a developing weather-maker in the Plains cranks up. We won't see the effects of it directly under Friday night at the earliest, so most of your day Friday should be windy and warm with very low chances of rain. Highs will be into the 70s. We might be aiming a little low at 72°.


The Plains system moves east Friday night with a cold front moving through early Saturday based on latest model data, which can be iffy that far out this time of year but could bring some strong storms. We'll be watching...


It does appear that an upper level low pressure trough could linger into the weekend over the area though, even if the front moves through, which may provide more more clouds and scattered showers into the weekend, as well as cooler temperatures. Prepare for the possibility of an "unsettled" first weekend of spring. Here are details on the week ahead:


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

Tuesday, March 14, 2017

The Middle of March - Winter Fights Back

Winter, are you here? The people of Memphis are a bit confused. With spring right around the corner, why are we talking about snow and cold? We're here to give you the answers straight from Mother Nature herself. But first, we have to start north.

Nor'Easter Brings Cold Air South
While Memphis sits under cloudy skies and chilly temperatures, the Northeast into New England are being plowed over by a strong nor'easter. This type of winter storm, named for the winds often associated with them, is bringing high winds and heavy snow across the region. Some areas are picking up over two feet of the white stuff, burying cars and knocking out power along the way.

The GOES-East satellite shows the strong comma-shaped structure of the nor'easter slamming the Northeast and New England.
What does this mean for the Mid-South region? Cold air has funneled in behind this system, prompting Freeze Watches and Warnings around our area for the next two nights. With clearing skies and less clouds in the air, temperatures will fall off significantly, and the same is possible tomorrow. Mid to upper 20s are possible around the area on Tuesday night, including in Memphis proper. While highs tomorrow only hit the low 40s, overnight lows on Wednesday night rebound slightly to near 30.

Make sure you are prepared for the cold these next two nights. Protecting the three P's will be essential - your plants, your pets, and your pipes. Plants especially that are left outdoors in these below freezing temps will be severely damaged by the unseasonable drop.

The National Weather Service Office in Memphis pushed out this graphic on Tuesday evening. Key takeaway - bring your plants indoors or cover them if you want them to stay alive.

Warming with Rain Coming

The cold air begins to push out of our picture by Thursday, as highs rise into the 50s and lows only drop into the 40s with overcast skies. However, with that warm-up comes the chance of rain to close out your week. A chance of showers builds in on Friday and continues on Saturday. These will likely not completely wash out the start of your weekend, but keeping the umbrella or rain jacket handy wouldn't hurt.

Temperature wise, the approaching low-pressure system will usher in warmer air from the south and southwest, progressively bringing temperatures back to normal. Highs on Friday will reach to near 60, and Saturday will hit the mid-60s.

The National Weather Service surface analysis for Thursday morning shows the potential for rain showers wrapping around the backside of high pressure and ahead of a weak low entering the Great Plains.
As high pressure builds in behind the showers, Sunday will see sunnier skies and temperatures into the upper 60s during the day. That warming trend continues into the beginning of your work week, just in time for the students returning from spring break. Highs on Monday and Tuesday should both break 70 degrees, though a slight chance of storms rumbles in by Tuesday afternoon.

March Ends Like a Lion or Lamb?
After March rolled into the Memphis area like a lion just a few short weeks ago, will Mother Nature bring a more peaceful transition to spring? Temperatures look to remain above average, much like what we have seen in January and February. Rain chances, however, could be slightly below average to right on par for this time of year.

Are you excited for spring? Before you know it, it will be April. And as they always say, April showers bring May flowers.



Be sure to check our MWN forecast for the latest updates, all generated by the men and women behind this site. Also download the MWN app for weather at your fingertips, including StormWatch+, the best severe weather tool to give you pinpoint watches and warnings.

Alex Herbst, Meteorologist
MWN Social Media Intern

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Follow MWN on Facebook, Twitter, and Google+
Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
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