SPC Mar 8, 2024 1300 UTC Day 1 Convective Outlook

[NorthGeorgiaWX]

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0655 AM CST Fri Mar 08 2024

Valid 081300Z - 091200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TEXAS TO
SOUTHERN ALABAMA...

...SUMMARY...
A tornado threat exists today into tonight from parts of Louisiana
to southern/eastern Alabama.  Large hail or strong-severe gusts are
possible over the same areas and westward into parts of north and
east Texas and southeastern Oklahoma.

...Synopsis...
Broadly cyclonic flow, astride increasingly phased northern- and
southern-stream troughing -- will shift eastward across the central
CONUS through day-1.  Through this period, the southern-stream
component -- with a series of vorticity maxima initially extending
from the Desert Southwest to the southern Plains -- will remain more
influential.  The associated trough should reach central KS, the TX
South Plains, and northern Chihuahua by 00Z.  By 12Z, the northern
part of the trough will reach the Ozarks and begin phasing with a
northern-stream shortwave trough digging southeastward across the
upper Mississippi Valley.  The southern trough will extend from the
Ozarks southwestward over central/southwest TX to the Big Bend
region.  Several meso-alpha- and smaller-scale vorticity lobes (some
convectively generated/augmented) should traverse the foregoing
southwesterly flow aloft.

At the surface, 11Z analysis showed weak lows near ACT and ABI,
which should consolidate toward the eastern low in the next few
hours.  A cold front extended south-southwestward to just downstream
from DRT on the Rio Grande.  A diffuse warm-frontal zone was drawn
east-southeastward across east TX, central/southeastern LA, and the
Gulf offshore from AL and the FL Panhandle.  The cold front should
reach to near a JAN-GLS-MFE line by 00Z, then from central AL
southwestward across southeastern LA to the northwestern Gulf by 12Z
tomorrow.  The warm front will remain diffuse while shifting
northeastward over southern parts of MS/AL and the western FL
Panhandle, ahead of a convective plume discussed below.  

...TX/OK to Gulf Coast States...
Multiple episodes of thunderstorms are expected across the outlook
corridor today, with the greatest potential for well-organized,
surface-based convection from parts of east TX eastward to near the
GA/AL line, in and near the "slight risk" area.  Severe gusts,
isolated large hail and a few tornadoes are all possible.  Potential
appears to be tied primarily to three regimes, with isolated
warm-sector supercell(s) possible south and southeast of them:

1.  An initially elevated corridor of precip and embedded
thunderstorms -- now apparent in composited radar imagery over
portions of western/central MS and northern LA.  This activity
should persist and expand lengthwise somewhat as the foregoing
airmass destabilizes today -- with sustained low-level warm
advection in its inflow layer lowering the elevation of effective-
inflow parcels to surface-based with time over the Gulf Coastal
Plain.  Modest lapse rates aloft will be offset to some extent by
increasing low-level theta-e with time and with southwestward
extent, as mid/upper 60s F surface dewpoints spread east-
northeastward through the day to meet the convective plume. 
Diabatic heating will be steady and modest, owing to persistent
cloud cover, but MLCINH should decrease with time across much of the
area south of about I-20.  Favorable deep shear is expected
(effective-shear magnitudes around 45-60 kt) along with variably
large hodographs and 150-300 J/kg SRH in the lowest km.  This will
yield a favorable supercell/tornado environment, but dominant
messy/training convective modes may limit overall organization of
severe potential somewhat.

2.  Thunderstorms initially in a band from north-central to south-
central/southwest TX, near the I-35 corridor and the low/cold front,
may increase severe potential as they shift eastward into the
western fringes of the environment discussed above, through the
remainder of the morning.  Some of this activity may merge with the
southwestern part of the initially separate first regime to create a
very long swath of strong-severe thunderstorms by mid/late afternoon
from southern AL to southeast TX.  The combined swath of convection
should shift slowly eastward/southeastward over the remainder of the
outlook area into tonight, maintaining potential for damaging gusts
and a few embedded tornadic mesocirculations.

3.  An afternoon area of thunderstorms rooted in or just above the
boundary layer poleward of the low and frontal zone, across parts of
OK and north TX, and spreading southeastward with mainly large-hail/
isolated-gust potential before weakening this evening.  Despite the
cool surface conditions, some convection may be rooted at or near
the surface, with cold midlevel temperatures nearest the trough
aloft contributing to steep low/middle-level lapse rates and MUCAPE
potentially reaching the 1000-1500 J/kg range.  Strong mid/upper
flow will contribute to effective-shear magnitudes of 40-50 kt,
supporting organized convective potential.

..Edwards/Jewell.. 03/08/2024

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