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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