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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