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!


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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