Tuesday, March 11, 2025

SPC Day 4-5 Outlook



This event is looking more like it has the potential to be a severe weather outbreak. On Friday it will be centered on the Mississippi River Valley, but by late Friday night or the very early hours of Saturday morning, the Tennessee Valley may be dealing with the same storms that affected areas to our West. 

And then during the day Saturday, it looks like we could have a messy storm mode with multiple rounds of severe weather potential. We could see enough clearing during parts of the day to destabilize the atmosphere for the afternoon or evening hours, and somewhere in this broad time window, we could see supercell thunderstorms, clusters, before at least one squall line to finish things off. I remember yesterday some of the model guidance was hinting at more than one line of storms after the more supercell/cluster look. 

Sometimes a messy storm mode can prevent a full-blown severe weather outbreak and keep the severe weather a little more scattered in nature. But that's not always the case. And concern is increasing that this severe weather event may be significant for some of us. All modes of severe weather will be possible with this: Large hail, damaging thunderstorm winds, and tornadoes. The way things are trending, I would err on the side of caution and take this threat seriously. We're going to have the unstable air we didn't have for the last two events, and the wind shear is looking strong. That could translate to more storm damage, at least for a few spots across the region where the right ingredients come together for supercell thunderstorms. 



And Southern Middle Tennessee will be included in this risk as well as North Alabama, both Friday night and Saturday. Just know that there is a threat for organized severe thunderstorms, some of which could produce tornadoes, Friday night through Saturday. The threat may be more on Saturday, but it's important to have a NOAA Weather Radio on alert with battery backup Friday night in case anything happens overnight in your area. Or at the very least, make sure your cell phone would wake you up for a Tornado Warning (Wireless Emergency Alerts). Especially if you live in a mobile home, you need to plan ahead for this one. This has the potential to be a fairly significant severe weather event with multiple rounds of storms. 

So it's very important to have a tornado safety plan in place before the weather turns ugly. It's not unusual for us to have threats like this in the Spring months, especially March and April. I remember in 2020 we had a pretty stout outbreak of severe thunderstorms and tornadoes on Easter Sunday. It didn't get quite as bad as it looked like it could around here, but it was still a significant event for the people impacted. And even in North Alabama alone, there were plenty of people impacted. It wasn't something unprecedented, but it was well worth taking seriously. And that's how I'm feeling about this setup. 

One event that keeps showing up as an analog is the January 30, 2013 event, which ended up only grazing the Tennessee Valley but produced significant damage through other parts of the Southeast and up into the Ohio Valley. And it did bring us a couple tornadoes around here too. 

Every event is unique, and it can be the luck of the draw where the mesoscale features set up to produce the most (or worst) severe weather. We could be in the zone that gets less, or less significant storms with this. Or we could be in the unlucky zone this time. If there's one thing I've learned over the years, it is that you should have a healthy respect (not a paralyzing fear, but a healthy respect) for any severe weather threat. Just have your plans, stay aware, and get to the safest place you can within your means if a tornado or severe thunderstorm is coming in your direction. Most of the time, you can come out of your shelter and breathe a sigh of relief. But once in a while, taking shelter in a severe weather outbreak literally saves somebody's life. So I wouldn't get hung up in the YouTube videos or other social media that might overblow the danger of this severe weather setup. But I would definitely take it seriously and respect the risk. It is 3-4 days away now. There is time to prepare. 

ZCZC SPCSWOD48 ALL

   ACUS48 KWNS 110849

   SPC AC 110849


   Day 4-8 Convective Outlook  

   NWS Storm Prediction Center Norman OK

   0349 AM CDT Tue Mar 11 2025


   Valid 141200Z - 191200Z


   ...DISCUSSION...

   ...Days 4-6/Fri-Sun - Mid/Lower MS Valley to the Southeast and

   Mid-Atlantic...


   An intense spring storm system will deliver a multi-day severe

   weather episode to portions of the central and eastern U.S.

   beginning Friday and continuing through the weekend. All severe

   thunderstorm hazards are expected, including widespread damaging

   winds, tornadoes (some strong), and large hail.


   On Friday, an anomalously intense upper cyclone is forecast to

   deepen as it tracks northeast across the southern/central Plains to

   the Upper Midwest. An intense jet streak (greater than 100 kt at 500

   mb) will overspread the Ozarks and Mid-MS Valley during the

   afternoon into the overnight hours. Likewise, a low-level jet will

   intensify Friday night to 65+ kt. As intense surface cyclogenesis

   occurs, southerly low-level flow will transport modest moisture as

   far north as eastern IA, southeast MN and southern WI. Deeper

   boundary-layer moisture will remain focused southward from the

   Mid-South toward the Lower MS Valley/central Gulf coast.

   Nevertheless, strongly forced convection within intense deep-layer

   flow will pose a widespread risk for severe (potentially significant

   severe) thunderstorm winds and tornadoes from late afternoon into

   the overnight hours across a large area centered on the Mid/Lower MS

   Valley vicinity.


   On Saturday, the upper cyclone over the Upper Midwest will lift

   northeast into Ontario, but a larger-scale upper trough will remain

   over the Plains. The Plains trough will intensify and spread east

   toward the MS/OH Valleys. This will maintain the eastward

   progression of a strongly forced line of convection from the Ohio

   Valley south/southwest into the Deep South/central Gulf coast

   vicinity through Saturday night. Portions of the Deep South into GA

   may see multiple rounds of severe convection with a mix of both

   supercell and QLCS storm modes potentially moving across the region,

   posing a concern for damaging tornadoes and swaths of severe winds.


   On Sunday, the system will continue to shift east, with a moist

   airmass and strong deep-layer flow continuing to support a line of

   convection producing damaging winds into the Carolinas and

   Mid-Atlantic vicinity.


   Outlook areas will continue to be refined over the coming days as

   key features become better resolved.


   ..Leitman.. 03/11/2025

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