SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0744 AM CDT Wed Mar 30 2022
Valid 301300Z - 311200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
WESTERN TENNESSEE...EASTERN ARKANSAS...NORTHERN/EASTERN
LOUISIANA...MISSISSIPPI...WESTERN/SOUTHERN ALABAMA...AND THE WESTERN
FLORIDA PANHANDLE...
...SUMMARY...
A regional outbreak of severe thunderstorms is expected from the
Lower Mississippi Valley into parts of the Ohio and Tennessee
Valleys today, and over portions of the central Gulf Coast states
later today into tonight. The greatest concerns are tornadoes (some
strong, EF2+) and severe gusts (some to hurricane force).
...Synopsis...
In mid/upper levels, a progressive, highly amplified pattern will
persist, featuring a complex synoptic-scale trough shifting eastward
over the central CONUS. A strong shortwave trough will dig
southeastward over the northern/central High Plains through today,
then pivot more eastward over KS/OK by 12Z tomorrow. As that
occurs, a strong/basal shortwave trough -- now evident in
moisture-channel imagery from central KS to the TX Big Bend region
-- will pivot eastward to northeastward, becoming neutrally then
negatively tilted today. The lead shortwave trough will eject
northeastward and lose amplitude tonight, leaving behind a field of
strong southwest flow through the mid/upper troposphere in the Ohio
Valley and much of the South, ahead of the main synoptic trough.
At the surface, the 11Z analysis showed a low over west-central IA.
A warm front -- drawn across northern MO, southern IL, and western
KY, will move northward across much of southern/central portions of
IL/IN through the day. An arctic cold front was drawn from the low
across southeastern KS, central OK, and northwest TX, to
southeastern NM. A Pacific cold front largely has overtaken the
dryline, and was drawn from western parts of north-central TX to
near HDO, then southwestward into central Coahuila. The arctic
front will overtake the Pacific front from north to south through
the period. By 00Z, the low should reach northern IL or southern
WI, with primary cold front roughly southward over IL and extreme
western KY, western TN, northern MS, central LA, and near mid/upper
coastal areas of TX. By 12Z, the low should occlude over western to
northern Lower MI, with the cold front over parts of WV,
northeastern TN, northern /western GA, the FL Panhandle, and the
north-central Gulf. The bulk of convection and severe potential
will remain ahead of the cold front.
...Gulf Coast to lower Ohio/mid Mississippi Valleys...
A band of convection, with embedded strong/locally severe
thunderstorms, is ongoing from the west-central Ozarks to northeast
TX. See SPC tornado watch 75 and related mesoscale discussions for
near-term guidance on associated severe potential.
As the basal shortwave trough pivots out today, strong height falls
and rapidly increasing low/middle-level wind fields will spread
farther over the warm sector adjacent to the ongoing, eastward-
shifting convective band. In keeping with that mass response and
the geometry of the height/vorticity fields, the convective band
should pivot toward a more meridional alignment as well.
Strengthening of both deep ascent and low-level moisture/theta-e
will reduce MLCINH observed in this morning's 06Z and 12Z
warm-sector soundings, contributing to increasing intensity and
coverage of thunderstorms in the main band, as well as some
potential for convection to develop to its east. How much sustained
convection can form ahead of the line will strongly influence the
tornado threat, which will be strong with the main line, but which
will be especially intense for any sustained supercells that can
form to its east.
The most-favorable parameter space still appears to be across the
"moderate" area, where the greatest wind and tornado probabilities
are drawn (including at least 10% significant-severe levels). In a
northward-narrowing wedge of favorable warm-sector boundary layer,
mid/upper 60s F surface dew points should become common from the
Gulf Coast to parts of the Mid-South, decreasing northward to the
mid 50s to low 60s south of the warm front, over outlooked parts of
IL/IN. Though diurnal heating will be modest over most of the area,
a combination of theta-e advection and cooling aloft will contribute
to MLCAPE ranging from 500-1500 J/kg over parts of LA/MS/AL mainly
south of I-20, decreasing to the 100-500 J/kg range near the Ohio
Valley.
Shear will be strong across the entire region, as 90-110 kt of
700-500-mb layer flow develop ahead of the ejecting shortwave trough
over the Mid-South, along with a broad, 60-85-kt LLJ. Forecast
soundings reasonably depict 50-70 kt effective-shear magnitudes,
along with large, well-curved hodographs fostering 300-600 J/kg
effective SRH (locally higher). This will support line-embedded
tornadic supercells and LEWP/mesovortex features, as well as bowing
segments to locally maximize destructive-wind potential. Any
preceding, sustained supercells that do develop would be fast-moving
(around 50 kt based on the Bunkers algorithm), with potential for
long tornado tracks if storm-scale occlusions are not very rapid.
Downward momentum transfer from layers of intense gradient flow in
low/middle-levels also my augment the severe-downdraft threat, with
bursts of hurricane-force gusts possible.
The convective regime should weaken with time and eastern extent
this evening and overnight across the Ohio Valley region, but may
persist at severe levels through the night across the Gulf Coastal
Plain as far east as eastern/southern AL, western GA and the FL
Panhandle, where sporadic severe gusts and at least a few tornadoes
will remain possible overnight.
..Edwards/Broyles.. 03/30/2022
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