2025-03-04 EVENT: AR/LA/MS/TN/MO/IL/KY

[Dan Robinson]

Meteorological spring will arrive with a significant negatively-tilted trough sweeping through the central US, pulling some moisture northward underneath of the 100kt+ jet streak for a potentially big supercell/tornado day in the middle/lower Mississippi Valley. Medium-range models agree on the evolution of the upper pattern, with the trough becoming negatively tilted from Monday onward as it moves out into the Plains and Midwest. Moisture surges north, with the 60F line making into northern Arkansas by midday Tuesday.

The basic ingredients are there for a major event of course, but I see a couple of big problems with this setup. The main one being is that the upper forcing is just too great. Mr. T saying "SEE WHAT TOO MUCH LIFT DOES?" comes to mind here (from Tim Vasquez's "Mr. T's chase forecasting school" cartoon). What is shown now seems to support a monster squall line getting started on Monday night and racing across the primary threat region through the day Tuesday. Parameters are shown maxing out at midday in the far southern regions as the squall line pinches off the warm sector, leaving everything north of I-40 cut off.

The second problem is the thermal/moisture profile. Forecast soundings show the lower levels at/close to saturation through most of the column, signalling tons of clouds. It's hard to find much of an EML anywhere in this setup to help counter the overpowering forcing.

The one area I'm looking at now (and part of that may be my home target bias talking) is a small area of clearing shown breaking through behind the main squall line and just ahead of the front in Missouri. It's close to the surface low and has a workable wind profile, but the moisture/thermal profile shown is quite meager - and that's if we *can* get any dry slot to allow for some sunlight there. As for the more potent areas farther south, it strikes me as typical Dixie: fast-moving grunge, mostly after dark, mostly embedded in a broken squall line, race-car speeds. Not very appealing compared to a shorter mostly-daytime outing closer to home. The southern region will of course need to be watched, as it could easily become sig-outbreak-caliber as more data comes in.

EDIT: The 00z NAM shows a more favorable initial state for Tuesday, with slower timing and more of an EML showing up over the warm sector.

 

[Dan Robinson]

Now that we're within CAM range of this event, the cold core aspect near the low in central Missouri is looking like a more viable target, but models still differ on whether we will see clearing behind the morning wave of storms. If that occurs, an arc of supercells looks likely to sweep across the state during the late afternoon/evening hours. Tornado potential looks limited by dewpoints only peaking in the upper 40s, much like today's event in Oklahoma. I would prefer an I-70-based chase of this in better terrain that would make for easy cell-hopping eastward, but this zone may end up farther south along the much more difficult-for-visibility I-44 corridor. The faster HRRR has the best-looking portrayal at the moment, with a nice interval of daytime supercells along the occluded front.

 

[WallsC]

I'm thinking the best chance for a chaseable storm or two is going to be along or south of the I-20 corridor in MS between I-55 and I-59 on Tue late afternoon, but it’s definitely not guaranteed.

I agree with you that we are looking at a classic, nasty Dixie setup with a violent squall line rolling through AR-LA-MS at breakneck speed on Tue evening into the overnight. The NAM makes it look particularly nasty along the Gulf Coast.

The question is going to be whether any discrete supercells can form up in advance of that inevitable line. The NAM and HRRR show decent bulk shear and SRH across south-central MS by the afternoon. Dew points also look promising as well, in the high 50s-low 60s. However, the atmosphere doesn't look to really destabilize until late evening into the overnight, with pretty unimpressive lapse rates and benign CAPE values during daylight hours.

It is somewhat tempting as an area I can get to within a few hours. Somewhat.