Latest from SPC

 

All of us in the TN Valley (North Alabama into Southern Middle Tennessee) are now included in a Level 3 out of 5 Enhanced Risk for severe weather tonight/into early tomorrow morning. Main threat is severe thunderstorms capable of damaging winds, but a few instances of large hail, and even isolated tornadoes will also be possible. If we were to see any supercell thunderstorms apart from the squall line, the most likely zone is in far Northwest Alabama around Muscle Shoals up through places like Waynesboro or Lawrenceburg in Tennessee. 

North Alabama will probably see the threat from about Midnight to Daybreak, but Tennessee counties could see the severe weather ramp up as early as 9-10 PM tonight. Even farther into North Alabama, an isolated supercell thunderstorm is a possibility, though the chance is low. Our main threat will come with the squall line itself for most places, both on the Alabama and the Tennessee side. Where any supercells can become discrete or semi-discrete from the squall line (or a storm cluster called a mesoscale convective system, could see either or both modes), there is a better chance of a tornado developing and staying on the ground a while, also a threat for very large hail, up to about the size of golfballs. 

Most of the severe weather should be over by 7 AM tomorrow, but some of it could last until about 8-9 AM for at least Northeast Alabama. It's a close call. 

Most of us have a 30% chance of damaging winds from this squall line, but for places like Hartselle, Decatur, and Athens, all back through Northwest Alabama and also up into our Tennessee counties including cities like Fayetteville back to Lawrenceburg and Waynesboro, the chance of damaging winds is 45%, so just about 50/50 within 25 miles of a given point, chance of a damaging wind event, at least enough to damage trees and power lines or bring them all the way down in some cases. 

The hail threat is looking more marginal as long as we mainly get impacts from the squall line without any semi-discrete supercells in the mix of what could be a sort of messy storm mode. Around Florence, Lawrenceburg, points West/Northwest is a better chance of seeing severe hail. Most of it should be measured in coin sizes. If we get any supercells capable of hail up to golfball size, should be an isolated episode or two out of this system. 

And most of us just have that general threat for isolated tornadoes being possible. But from about Hamilton up to Athens, Shelbyville, Lawrenceburg, and points North and West, the chance of tornadoes is a little enhanced, up to 10%. The hatching notes were it's more likely to see supercell thunderstorms within or ahead of the squall line that could potentially produce more significant tornado damage than average. 

If you get a Tornado Warning tonight, you need to be out of a mobile home and into a sturdy site-built house or other strong building. And get into a small interior room (or hallway) on the lowest floor, away from windows. If you have time, get up under something sturdy or use whatever is available to shield your body, especially your head, from any falling or flying debris. 

For a Severe Thunderstorm Warning, usually you don't have to take quite the same level of precaution as for a Tornado Warning, but I wouldn't completely ignore it either. At least get away from windows and electrical stuff until the storm passes. And I wouldn't be in a mobile home or a top-floor apartment near a window with trees around if I could help it. Once in a while, it's a good idea to go to your shelter room even for one of these warnings. People have different risk tolerance levels. It's still good to be on a lower floor away from any windows, and if you can help it, in a sturdier structure than a mobile home. 

Main thing is just getting the warning more reliably than from an outdoor siren. Have Wireless Emergency Alerts enabled on a cell phone ready to wake you up. And if you have it, make sure your NOAA Weather Radio is set properly to alert you, with battery backup. Some local radio stations are good to sleep to, that will cut in for severe weather, if you don't have a weather radio. It's more likely to wake you up than television, because they often sound that really abrasive emergency alert tone before they broadcast the warning. 

If you know somebody in the path of a really dangerous storm tonight, especially a tornado, give them a call if you need to make sure they're awake. They'll get over any grouchiness. It's better than somebody sleeping through it and getting hurt. 

3:38 PM - We do have some severe thunderstorms firing up and already trying to form clusters or a rough line in Arkansas, Eastern Missouri, stretching up into the Ohio Valley. But it will be roughly eight hours or so before we have to deal with such things around here. 

3:42 - And here I go testing out a new radar I may use on this blog. 

SPC AC 301939

   Day 1 Convective Outlook  

   NWS Storm Prediction Center Norman OK

   0239 PM CDT Sun Mar 30 2025

   Valid 302000Z - 311200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF

   THE LOWER/MID MISSISSIPPI VALLEY INTO THE OHIO VALLEY AND SOUTHERN

   GREAT LAKES...

   ...SUMMARY...

   Numerous severe thunderstorms are expected through tonight across a

   broad portion of the Southeast and lower/mid Mississippi Valley into

   the Ohio Valley and southern Great Lakes. Multiple swaths of

   widespread damaging winds appear likely. Large to very large hail

   and several tornadoes will also occur with supercells. A few of

   these tornadoes could be strong.

   ...20z Update...

   Minor adjustments were made to the D1 Outlook to remove portion of

   the Marginal across north-central Texas into Missouri behind the dry

   line. Further development along the dry line into Arkansas is

   expected through the afternoon/evening. Daytime heating has allowed

   an axis of MLCAPE around 1500-3000 J/kg to develop from far southern

   Texas into Louisiana. This will continue to nose northward into

   portions of Arkansas through time, with weakening of MLCIN.

   Supercell development is expected with potential for very large hail

   with any stronger discrete supercells. 

   Further north, minor adjustments were made to the Marginal and

   Slight in the Midwest behind ongoing convection and cold front.A

   line of thunderstorms continues eastward across portions of Indiana

   and central/northern Illinois. This line has produced measured

   severe gusts 60-70 mph and will likely pose a continued damaging

   wind threat across central/northern Indiana/southern Michigan

   through the afternoon/evening. A favored corridor of stronger wind

   is possible across central/northern Indiana, as has been indicated

   in recent WoFS runs. 

   See previous discussion for more information.

   ..Thornton.. 03/30/2025

   .PREV DISCUSSION... /ISSUED 1121 AM CDT Sun Mar 30 2025/

   ...Synopsis...

   Water-vapor imagery late this morning shows a lead mid-level

   shortwave trough moving quickly northeastward across MO, while an

   upstream disturbance over the TX Panhandle/western OK rounds the

   base of a larger-scale trough over the central U.S.  Surface

   analysis places a cyclone near the IA/IL/WI border with a trailing

   cold front south-southwestward through the lower MO Valley and into

   eastern OK and north TX.  This front will push east through the OH

   Valley and into the lower MS Valley by early Monday morning and

   focus thunderstorm development.  

   ...Midwest/Ohio Valley to the Great Lakes...

   Visible-satellite imagery shows cloud breaks to the immediate east

   of the lead mid-level disturbance as a moist/warm conveyor (40-kt

   southwesterly LLJ) maintains a fetch of seasonably rich moisture

   into the region.  Additional thinning cloud cover and heating

   through the early to mid afternoon will lead to thunderstorms

   developing and intensifying.  A belt of 50-80 kt 500-mb flow will

   overspread the destabilizing airmass and yield ample deep-layer

   shear for organized convection.

   The stronger early storms will favor supercell and banded linear

   modes, with the supercells posing a threat for large to very large

   hail (around 1.5-2.5 inch diameter) given the presence of steep

   mid-level lapse rates and favorable deep-layer shear.  Meridional

   upper-level flow from I-70 northward will favor a quicker transition

   to linear structures compared to farther south/southwest, where

   hodographs will promote a longer window of opportunity for cellular

   (discrete and clusters) storm modes.  The tornado risk will be

   greatest with quasi-discrete supercells (potentially a few strong

   tornadoes) near and south of the OH River, but some tornado threat

   will probably develop with a squall line as it matures through the

   afternoon/evening.  As storm coverage increases, multiple swaths of

   numerous to potentially widespread severe/damaging winds appear

   likely as one or more clusters moves quickly east-northeastward over

   the OH Valley and southern Lower MI. The threat for damaging winds

   and tornadoes should continue this evening into the overnight hours,

   until convection outpaces the low-level moisture return and

   eventually weakens over the upper OH Valley and central

   Appalachians.

   ...Central/East Texas into the Lower/Mid Mississippi

   Valley/Mid-South and Southeast...

   Strong destabilization is anticipated across the Ark-La-Tex east and

   northeastward into the Mid South.  Rich low-level moisture (mid to

   upper 60s to around 70 deg F dewpoints) will stream northward across

   TX ahead of the dryline, and the lower/mid MS Valley and Southeast

   ahead of the cold front.  Model guidance continues to indicate rapid

   and intense thunderstorm development during the afternoon from parts

   of north/east TX northeastward into AR.  Supercells are expected

   initially, with 40-50+ kt of deep-layer shear supporting robust

   updraft organization and rotation.  A favorable setup exists for

   large to very large hail with the stronger supercells.  

   It appears the greatest risk for several tornadoes will focus

   over parts of the Mid-South from eastern AR into western TN on the

   southern periphery of an intensification of 850-mb flow towards

   evening.  Forecast soundings show moderate to locally strong

   buoyancy (2000-3000 J/kg MLCAPE) on the northern rim of 66-68 deg F

   dewpoints, and co-located with strong southwesterly flow veering to

   westerly by early evening.  It is during the 22-04 UTC period in

   which forecast hodographs enlarge in the low levels and become more

   favorable for discrete supercells.  The strong tornado risk may

   maximize within this corridor from parts of eastern AR eastward into

   western and perhaps Middle TN during the evening.  Additional severe

   storms are probable farther south as activity from the Ark-La-Tex

   moves east into the lower MS Valley and central Gulf Coast states

   during the late afternoon into tonight.  In addition to large to

   very large hail, damaging gusts and a tornado risk will likely

   accompany the stronger storms with a gradual lessening in overall

   coverage and intensity during the late night.

   ...Florida Peninsula...

   A weak mid-level perturbation will move eastward over FL this

   afternoon.  Modestly enhanced winds aloft, and a veering profile

   with height through mid levels, should support sufficient deep-layer

   shear for strong to severe multicells.  The stronger diurnally

   driven storms may be capable of severe hail and damaging winds.