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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0746 AM CDT Wed May 25 2022

Valid 251300Z - 261200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EASTERN LOUISIANA...MISSISSIPPI...AND WESTERN ALABAMA...

...SUMMARY...
Strong to severe thunderstorms are possible from the central Gulf
Coast into parts of the lower/mid Mississippi Valley, Southeast,
Midwest, and Ohio Valley.

...Synopsis...
The main mid/upper-level feature for this forecast will be a
well-defined synoptic trough now over the Plains States southward to
northeastern MX, with a 500-mb low re-forming across western OK at
this time.  The low should move erratically northeastward to near
the southern part of the KS/MO line by 12Z tomorrow, with trough
southward across the Arklatex and western Gulf.  Small, convectively
induced/augmented vorticity maxima will eject northeastward to
northward ahead of the trough, across parts of the lower/mid
Mississippi and Ohio Valleys, Tennessee Valley and central Gulf
Coast.

At the surface, 11Z analysis showed a low over northeastern KS, with
a cold front arching across the OK/MO border area, northeast TX, and
east-central TX, to near LRD.  The cold front was preceded by a
convective/outflow boundary from northeastern MX and near BRO
northeastward across western LA.  A warm front was drawn over
northern MO, north-central IL, and central portions of IN/OH, though
several areas of convection have altered the sector south of the
synoptic warm front. The cold front should move eastward slowly
across much of AR and LA through the period, preceded at least into
this evening by the convective boundary.  Meanwhile, the low should
split, with one part moving northeastward along the warm front to WI
tonight, and the other stacking more vertically with the mid/upper
cyclone center.

...Gulf Coast States, Delta region, Mid-South, TN Valley...
Scattered thunderstorms are possible in multiple episodes through
the period, the main one likely being associated with a band of
convection now extending from western LA across the northwestern
Gulf.  Sporadic damaging winds and a few line-embedded tornadoes are
possible.  This activity, and the associated corridor of outflow-
aided convective lift, are expected to shift eastward into a
low-level air mass destabilized by a co*bination of:
1. Theta-e advection from the south, with 70s F surface dew points
already co*mon south of I-20 between western AL and western LA;
2. Patchy areas of diurnal surface heating, in relative breaks of
cloud cover between the convective band and a separate area of
thunderstorms initially over AL and the western FL Panhandle.

These factors should offset modest midlevel lapse rates enough to
support MLCAPE near 2000 J/kg over southern LA/MS, decreasing to
around 500-1000 J/kg northward over parts of the Mid-South region. 
Mid/upper-level winds and deep speed shear will increase with time
as the synoptic trough approaches, but with little change in
direction in the vertical profile.  As such, forecast soundings show
peak effective-shear magnitudes only reaching the 30-40-kt range,
supporting organized multicells, QLCS mode, short-lived supercell
structures, and a few bow/LEWP formations with associated
mesocirculations.  

Additional strong/isolated severe thunderstorms may persist this
morning across the east-central Gulf Coast region from the FL
Panhandle into AL, as well as develop behind the remnants of
original convective line tonight across parts of LA/MS/southern AL. 
The severe potential with the overnight activity (wind, perhaps
tornado) is more uncertain, and dependent on the extent of airmass
recovery behind the daytime co*plex.  However, the bulk of any such
nocturnal threat should be contained within the upgraded outlook
area as drawn.

...Eastern Ozarks, mid Mississippi/lower Ohio Valleys...
Widely scattered to scattered thunderstorms are expected to form
this afternoon in an arc along/ahead of the front, and northeast
through east of the surface low, over parts of northeastern AR and
eastern MO.  This activity should shift into IL before weakening
appreciably.  Widely scattered thunderstorms also should develop
today in a zone of increasing low-level moisture and slowly eroding
MLCINH in the partially modified warm sector across parts of
IL/IN/OH/KY ahead of the near-frontal arc.  At least a marginal
wind/tornado threat may develop, along with isolated hail.

The convective arc will be located in a zone of relatively maximized
deep-layer lift and low-level convergence ahead of the progressive
mid/upper cyclone, with relatively backed near-surface flow aiding
boundary-layer shear.  However, weak middle-level lapse rates and
muted surface heating due to cloud cover (limiting low-level lapse
rates) will temper buoyancy in this regime, which will be located
well north of the richest Gulf moisture.  MLCAPE generally in the
300-800 J/kg range is expected with little to no MLCINH left by
midafternoon, enabling development and maintenance of this activity,
which may link up with the northern extent of the LA/MS convective
band discussed above. If mesoscale trends and subsequent model
guidance indicate more destabilization (surface or aloft), or
stronger sustained lift, greater severe probabilities may need to be
extended north into this region.

..Edwards/Kerr.. 05/25/2022