DAY1SVR: Enhanced Risk SE
From
Dumas Walker@21:1/175 to
All on Mon Mar 25 08:41:00 2024
ACUS01 KWNS 251245
SWODY1
SPC AC 251243
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0743 AM CDT Mon Mar 25 2024
Valid 251300Z - 261200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN PARTS OF
EASTERN LOUISIANA AND SOUTHEASTERN ARKANSAS TO EASTERN
MISSISSIPPI...
...SUMMARY...
Tornadoes and damaging thunderstorm gusts are possible today through
tonight from east Texas to Alabama.
...Synopsis...
In mid/upper levels, a well-developed synoptic trough extends from a
cyclone over the central Plains southwestward across far west TX to northwestern mainland MX and central Baja. A series of shortwaves
behind the leading/synoptic trough will help to maintain larger-
scale cyclonic flow over much of the western/central CONUS and
northern MX through the period. However, the 500-mb cyclone should
move erratically across KS today into this evening, reaching parts
of northwestern MO, IA and southern MN by 12Z tomorrow. To its east
and south, a broad, strong fetch of cyclonically curving, roughly
southwesterly flow aloft will shift eastward from the Southern
Plains across the lower Mississippi, Tennessee and lower Ohio
Valleys.
At the surface, 11Z analysis showed a low near CNK, with Pacific/
leading cold front having overtaken the dryline and drawn through north-central/south-central TX to easternmost Coahuila. A polar
front was drawn from the low across northwestern OK, the southern TX
Panhandle and east-central NM. The low should move to west-central
IA by 00Z, with leading front reaching eastern parts of MO/AR,
northern LA, extreme southeast TX, and the northwestern Gulf. By
then, the polar front should extend southward over easternmost parts
of KS/OK to north-central TX, the northern Permian Basin region of
TX, and southeastern NM. By 12Z, the low should reach northwestern
WI, with the fronts essentially merged southward to western KY, and
the leading boundary from there across southeastern parts of MS/LA.
...East TX to AL...
A swath of precip and embedded convection -- including widely
scattered thunderstorms -- is apparent along and ahead of the
Pacific front, from portions of central TX into the Ozarks. Much of
this activity has exhibited a disorganized, anafrontal character for
several hours, as the leading boundary continues to progress
slightly rightward of storm motion. Overall severe potential should
remain marginal over the next few hours as that general character
persists.
However, severe potential should ramp up from midday onward across
the outlook area amid favorable/strengthening ambient deep shear.
Two processes will contribute to increased surface-based
convective/severe potential along this boundary from midday into
tonight:
1. Some slowing of the boundary and decrease in anafrontal
tendencies as it crosses the lower Mississippi River/Delta region,
and
2. The foregoing warm sector becomes substantially more buoyant
through a combination of warm advection, moist advection and
diabatic heating of the boundary layer -- especially from a few
counties north of I-20 southward. Forecast soundings reasonably
depict a northward-narrowing, triangular wedge of 500-1500 MLCAPE
shifting eastward over the region ahead of the main convective line.
While much more uncertain, discrete supercell development may occur
off the southern/southeastern part of the line, given progged
decrease in MLCINH in the free warm sector.
The geometry of the height gradient aloft -- around the southern rim
of the ejecting cyclone and associated/trailing shortwave trough --
still will maintain a strongly parallel flow component to the
primary band of convective forcing, helping to maintain quasi-linear
mode. However, given the strength of the deep shear (effective-
shear magnitudes of 55-65 kt), and of the low-level shear/hodographs
(effective SRH of 250-500 J/kg), the line will encounter in and near
the "enhanced" area, tornadoes are probable from associated LEWP/bow
formations and embedded mesovortices, as well as any supercells that
can mature enough before/during QLCS merger. The parameter space
will support significant (EF2+ damage potential) tornadoes as well,
though local storm mode/duration will strongly regulate that threat.
The QLCS gradually will outpace the favorable inflow-layer
thermodynamic regime from north-south, as it moves eastward into AL
overnight, but with southern parts still offering a severe threat.
...Lower Missouri Valley region...
Widely scattered to scattered thunderstorms should form this
afternoon near the surface low and polar front. Isolated,
marginally severe hail or gusts may be noted, and a tornado is
possible.
The airmass between the leading and polar fronts will remain
somewhat moist, with surface dewpoints in the 50s F over much of the
region. Diabatic heating and warm advection will contribute some
low-level destabilization, though its duration and strength will be
limited within a narrow corridor northwest of the cloud/precip
shield from the aforementioned main convective band. However,
large-scale lift preceding the ejecting mid/upper-level low and
trough should lead to cold air aloft (e.g., 500-mb temperatures
around -19 to -22 deg C), steepening low/middle-level lapse rates
and decreasing MLCINH through much of the afternoon. This should
support MLCAPE around 500 J/kg, with strong deep/speed shear and
potential for vorticity-rich low-level boundaries to augment
shear/hodographs locally. Convection should weaken soon after dark.
..Edwards/Wendt.. 03/25/2024
$$
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