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Severe Weather Threat May 20-21, 2025

Expanded 10% SIGTOR threat and a 45% wind risk added.
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT MON MAY 19 2025

VALID 201200Z - 211200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
MID-SOUTH AND TENNESSEE VALLEY...

..SUMMARY

SEVERE THUNDERSTORMS ARE LIKELY ACROSS PORTIONS OF THE MID-SOUTH,
TENNESSEE VALLEY, AND LOWER OHIO RIVER VALLEY ON TUESDAY, INCLUDING
DAMAGING WINDS AND TORNADOES, A FEW OF WHICH COULD BE STRONG.

..MID-SOUTH AND TENNESSEE/LOWER OHIO VALLEYS

RESIDUAL THUNDERSTORMS AND ASSOCIATED CLOUD COVER ARE EXPECTED TO BE
ONGOING ACROSS THE MID-SOUTH TO LOWER OHIO VALLEY TUESDAY MORNING,
WITH THE EARLY DAY EXTENSIVENESS OF THESE STORMS, AND RELATED
OUTFLOW/DIFFERENTIAL HEATING, TO BE KEY FACTORS, AND POINTS OF
UNCERTAINTY, REGARDING LATER-DAY SEVERE POTENTIAL. THIS WILL
ESPECIALLY BE THE CASE WITH NORTHWARD EXTENT TOWARD THE OHIO RIVER
AND NORTHERN PARTS OF THE CUMBERLAND PLATEAU.

ON THE SOUTH/SOUTHWEST EDGE OF THIS EARLY DAY ACTIVITY, RELATIVELY
RAPID AIR MASS RECOVERY AND DESTABILIZATION CAN BE EXPECTED, OWING
TO SUSTAINED LOW-LEVEL MOISTURE TRANSPORT FROM THE SOUTHWEST IN
TANDEM WITH CLOUD BREAKS AND AN ADVANCING MID-LEVEL DRY SLOT. THIS
WILL BE AS AN UPPER LOW SHIFTS NORTHEASTWARD OVER THE MIDDLE
MISSOURI VALLEY AND UPPER MIDWEST, WITH A CYCLONICALLY CURVED
MID/UPPER-LEVEL JET STREAK OVERSPREADING THE WARM SECTOR, WHICH
COULD BE CONVECTIVELY CONTAMINATED NEAR/NORTH OF THE OHIO RIVER. AT
LEAST MODERATE BUOYANCY IS FORECAST TO DEVELOP ACROSS THE
UNPERTURBED AND WEAKLY CAPPED WARM SECTOR BY EARLY AFTERNOON.

IT SHOULD BE NOTED THAT MULTIPLE SUB-REGIONAL AREAS, PARTICULARLY
ACROSS CENTRAL/EASTERN PORTIONS OF KENTUCKY AND TENNESSEE, COULD
RECEIVE MULTIPLE REPEAT-ROUNDS OF SEVERE STORMS ON TUESDAY.
THUNDERSTORM DEVELOPMENT WILL LIKELY OCCUR RATHER EARLY IN THE
AFTERNOON AS INHIBITION WILL BE QUICKLY ERODED AND DYNAMIC FORCING
FOR ASCENT OVERSPREADS THE WARM SECTOR. VERY FAVORABLE SUPERCELL
WIND PROFILES WILL EXIST ACROSS MOST OF THE REGION VIA THE MID-LEVEL
JET AND A DIURNALLY SUSTAINED 30+ KT LOW-LEVEL JET.

INITIAL SUPERCELLS WILL POSE A THREAT FOR ALL SEVERE WEATHER HAZARDS
INCLUDING THE POTENTIAL FOR STRONG TORNADOES, BUT A MIXED CONVECTIVE
MODE SHOULD EVOLVE AS UPSCALE GROWTH OCCURS INTO MULTIPLE CLUSTERS.
RELATIVELY WIDESPREAD DAMAGING WINDS, ALONG WITH A CONTINUED
MIXED-MODE TORNADO POTENTIAL, MAY OCCUR BY LATE AFTERNOON AND
EVENING AS STORMS SPREAD EAST-SOUTHEASTWARD TOWARD THE APPALACHIANS
VICINITY.

..CAROLINAS AND FAR SOUTHERN VIRGINIA

WEAK HEIGHT FALLS WILL BEGIN TO INFLUENCE THE REGION BY LATE IN THE
DAY WITH A WARM FRONT BEGINNING TO SHIFT NORTHWARD ACROSS THE
REGION. AT LEAST A CONDITIONAL OR ISOLATED POTENTIAL FOR SEVERE
STORMS INCLUDING SUPERCELLS WILL EXIST NEAR THE WARM FRONT AND
WITHIN THE IMMEDIATELY ADJACENT WARM SECTOR.

..GUYER.. 05/19/2025
Click to expand...
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Kinda off topic, but has anyone had any issues posting images? I've been trying to post a epic lightning shot I got on GoPro 11 early Saturday morning in Photography and it shows up a blank.
 
All CAMs have somewhat concerning solutions for tomorrow, but the NSSL is most troubling, depicting discrete supercells. Others have a mixed-mode capable of all hazards. Instability won't be an issue, and there will be a healthy overlap of strong SRH. TN, MS, AL and parts of GA should be monitoring this setup closely and tune their plans for tomorrow accordingly.
floop-hrrr-2025051912.refcmp_uh001h.us_se.giffloop-nam4km-2025051912.refcmp_uh001h.us_se.giffloop-hrwarw-2025051912.refcmp_uh001h.us_se.giffloop-hrwnssl-2025051912.refcmp_uh001h.us_se.gif
 
JPWX said:
Kinda off topic, but has anyone had any issues posting images? I've been trying to post a epic lightning shot I got on GoPro 11 early Saturday morning in Photography and it shows up a blank.
Click to expand...
Could be due to image filesize/quality? It's possible that high quality photos might have some trouble, though I haven't tried it myself.
 
FFC's morning AFD lays out the uncertainties for our area well. I think the biggest question for us in North Georgia will be how much overlap of favorable SRH we get, instability isn't really much of a question for most of the Southeast.
As the fairly robust May trough and associated sfc low traverse
the Ohio Valley, a cold front will swing through the southeast
bringing showers and thunderstorms with it. Confidence has
increased that favorable conditions for severe weather will be in
place ahead of the line as it enters northwest GA, however there
is significant uncertainty in the strength of the cold-front.
Models indicate the potential for a broken/diffuse cold front
resulting in more than one wave of uplift. This means increased
uncertainty in both timing and strength of any storms which may
develop. Current model timing spread sits at around 12 hrs, with
the fastest modes entering the CWA near 18z and the slowest
entering closer to 06Z (well after dark). Overall, timing could be
the difference between storms forming in a region of >2500 J/Kg
CAPE and 370m2/s2 0-3km SRH (Lots of storm juice) or <1000 J/Kg
CAPE and <100m2/s2 0-3km SRH (Not much storm juice). The closer to
peak heating and the more cohesive the cold front the higher the
storm potential. We will definitely need to keep an eye on this
timeframe, especially as more CAMs come into range.
Click to expand...
BMX says a lot depends on storm mode, with a more cellular mode supporting greater tornado threat.
.LONG TERM...
(Tuesday night through next Sunday)
Issued at 349 AM CDT MON MAY 19 2025

A cold front will approach Central Alabama on Tuesday evening, with
a threat of severe thunderstorms across the region. Storms will form
initially over Tennessee and northern Mississippi during the
afternoon hours, supported by SBCAPE values likely to be approaching
or exceeding 1800 J/kg. Activity is expected to grow upscale into a
more linear storm mode by the evening hours, which will move
southeastward into Central Alabama by late evening into the
overnight. New 06z CAMs suggest bulk shear values 50-60 kts, with 0-
1 and 0-3 SRH of 300-400 m2/s2. A strong mid-level jet that will
initially be supportive of supercells will contribute to favorable
conditions for tornadoes, especially further north across Tennessee.
There will be some question as to how storm mode may affect the hail
and tornado threat as the cells become line segments and ultimately
a line moving southeast across Central Alabama. Forecast LCLs of 500-
800 m are also generally favorable for tornadoes. The HRRR and 3 km
NAM depict little in the way of reflectivity with the line, with may
indicate the hesitancy of upscale growth. More cellular activity
making into Central Alabama, as opposed to linear, would greatly
increase the tornado and hail threat, especially across areas
northwest of the Interstate 59/20 corridor. Severity should
gradually decrease later overnight as the line sinks further
southeast toward the Interstate 85 corridor.
Click to expand...
 
Had to screenshot it, but it's posted now in Photography thread
 
Clancy said:
FFC's morning AFD lays out the uncertainties for our area well. I think the biggest question for us in North Georgia will be how much overlap of favorable SRH we get, instability isn't really much of a question for most of the Southeast.

BMX says a lot depends on storm mode, with a more cellular mode supporting greater tornado threat.
Click to expand...
Yeah, all signs are pointing to a semi discreet line or discreet storms (WRF-NSSL) Which isn't good. Considering the environment
 
Just sidenote: I don't know what has been up with the 3km NAM lately, but it has been lackluster with the threat tomorrow especially with showing storm activity. I mean it is concerning with not showing a super squall line, but I kinda expect more storms than it's showing.
 
JPWX said:
Just sidenote: I don't know what has been up with the 3km NAM lately, but it has been lackluster with the threat tomorrow especially with showing storm activity. I mean it is concerning with not showing a super squall line, but I kinda expect more storms than it's showing.
Click to expand...
It seems to have a fairly strong bias in underdoing convection - it's especially egregious during cold-season events.
 
Clancy said:
It seems to have a fairly strong bias in underdoing convection - it's especially egregious during cold-season events.
Click to expand...
Yeah which is why I've been using a combination of the HRRR/RRFS more
 
18Z HRRR shows a deep and rich warm sector, with DPs up to the lower 70s Tuesday afternoon. CAPE as high as 3,500 j/kg will provide more than enough fuel for any storms that develop in the afternoon. SRH ranging from 150-350 will be in place, and favorable hodograph curvature is evident. HRRR once again depicts a mixed-mode, with QLCS storms and possible supercells intermingling. Tennessee, western Kentucky, much of Mississippi, northern Alabama and northern Georgia all look to be in play.
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