Mesoscale Discussion 180

Issued

Mar 15, 2021, 2:35 PM CDT (19:35 UTC)

Expired

Mar 15, 2021, 5:00 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Birmingham radar (KBMX), 77 km from the middle of the area, began a volume at 19:37 UTC, the scan nearest the moment this went out.

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206 
ACUS11 KWNS 151935
SWOMCD
SPC MCD 151935 
ALZ000-MSZ000-152200-

Mesoscale Discussion 0180
NWS Storm Prediction Center Norman OK
0235 PM CDT Mon Mar 15 2021

Areas affected...portions of north-central to southwestern
AL...east-central/southeastern MS.

Concerning...Severe potential...Watch unlikely 

Valid 151935Z - 152200Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated damaging gusts or a tornado may occur this
afternoon with thunderstorms in a loosely organized band over AL,
and additional convection may build along the associated boundary
back into MS.  A watch does not appear likely at this time, but
conditions will be monitored for any increase in coverage or other
more-favorable convective trends that would upgrade the threat.

DISCUSSION...19Z surface mesoanalysis showed a convective/
convergence boundary (preceding a decaying, diffuse cold front) in
an arc from near HSV-TCL to just north of PIB, with the associated
outflow/thermal gradient extending further westward over southern
MS.  The boundary will move slowly eastward over northern AL, become
quasistationary near the state line, and may pivot northward through
the remainder of the afternoon across southern MS.  This will be the
main focus for development, though weakening MLCINH will enable some
potential for convection to form in the warm sector to its south as
well.  An eastern limiting boundary appears in the form of a theta-e
gradient (to lower dew points and somewhat lower temperatures) from
the western FL Panhandle northward, representing much stronger
MLCINH to its east.  Slow decay and eastward drift is possible with
this boundary.  

Modified RAOBs and forecast soundings show MLCAPE in the 1000-2000
J/kg range, amidst 50-60-kt effective-shear magnitudes.  Low-level
SRH favoring supercell potential is more confined near the
TCL-BHM-HSV corridor where hodographs are enlarged near and south of
the junction of those boundaries with a warm front, near HSV.  This
is sampled by the VWP from BMX, with 0-3-km SRH of 300-400 J/kg. 

Convection should continue to deepen across this corridor, as
diurnal destabilization continues to both:
1.  Increase low-level lapse rates/boundary-layer bouyancy and 
2.  Overcome a midlevel stable layer sampled by the 12Z JAN RAOB.
The main limiting factors appear to be lack of both upper support
and stronger low-level lift.

..Edwards/Grams.. 03/15/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BMX...HUN...MOB...JAN...

LAT...LON   31768929 32338829 33048772 33838718 34478692 34548665
            34398630 34028603 33648599 33148617 32648650 32088699
            31618740 31408802 31388873 31368931 31768929

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.