SPC AC 090521
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1221 AM CDT Wed Apr 09 2025
Valid 091200Z - 101200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Thunderstorms are possible across portions of the Midwest, the Upper
Midwest, and the northern High Plains, though severe storms are not
expected.
...Synopsis...
A shortwave trough in the northern Plains early this morning will
move southeastward into the mid-Mississippi Valley and undergo
modest amplification. A weak surface low will move swiftly
southeastward along with the trough. A warm front will be positioned
within parts of the Upper Midwest with a cold front southwestward
from the low into the central/southern Plains.
With the recent intrusion of cooler air into much of the Gulf,
moisture availability will be quite limited -- which is also quite
evident in this evenings observed soundings in the Southeast. Even
so, some thunderstorm activity will be possible as warm-air
advection into the warm front promotes lift. To the northwest of the
surface low, steep low/mid-level lapse rates may allow for isolated
to widely scattered storms in parts of the northern/central Plains.
...Mid-Mississippi/Lower Ohio Valleys...
Showers and thunderstorms are possible early this morning driven by
the amplifying shortwave trough and low-level warm advection.
Mid/upper-level clouds are already moving into the region late on
Tuesday and forecast soundings suggest some cloud cover will persist
into the afternoon as well. With a generally dry boundary layer and
weak destabilization, most activity in Illinois into the Ohio Valley
region will likely be elevated. severe potential appears quite
limited, but small hail could occur with the strongest storms.
Closer to the surface low/cold front in northeastern Missouri and
far west-central Illinois, it is possible that greater
destabilization could occur. Models show some signal for a narrow
zone of greater moisture return ahead of the front and these areas
will be on the eastern periphery of a steep mid-level lapse rate
plume. Current surface observations still suggest the moisture
return depicted in models may be too aggressive. If upper 40s F
dewpoints can reach farther north than expected, there would be some
potential for a surface based storm. The upper-bound severe
potential would likely be marginally severe hail. Uncertainty is too
high and coverage is too low for unconditional severe probabilities.
...Lower Missouri Valley Vicinity...
Despite dewpoints around the mid 30s F, very cold temperatures aloft
(-20 to -24 C at 500 mb) will support isolated to widely scattered
convection during the afternoon. Buoyancy is expected to be quite
weak, but large boundary layer dewpoint depressions could promote
some stronger wind gusts.
..Wendt/Squitieri.. 04/09/2025
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
SPC AC 090559
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Wed Apr 09 2025
Valid 101200Z - 111200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID/DEEP SOUTH AND TENNESSEE VALLEY...
...SUMMARY...
Scattered severe storms capable of producing large hail and damaging
gusts will be possible across portions of the Mid/Deep South and
Tennessee Valley.
...Synopsis...
A positively tiled large-scale trough will advance southeastward
from the Upper MS Valley/Midwest to the OH/TN Valleys through the
period. Within the base of the trough, a 70-80-kt west-northwesterly
midlevel jet will overspread the Mid/Deep South and TN Valley. In
response, lower/middle 50s F dewpoints will stream northeastward
along/ahead of a southeastward-moving cold front.
...Mid/Deep South and Tennessee Valley...
Along/ahead of the front, ample diurnal heating of the partially
modified Gulf moisture beneath steep midlevel lapse rates (upwards
of 8 C/km) will contribute to around 1000 J/kg MLCAPE. As ascent in
the left-exit region of the midlevel jet impinges on the
destabilizing air mass along/ahead of the front, a band of scattered
thunderstorms will develop across the Mid-South during the
afternoon. 50-60 kt of effective shear (characterized by a
long/straight hodograph) oriented perpendicular to the front will
favor discrete/semi-discrete supercells initially. The primary
concern with these storms will be large hail to around 1.5-1.75
inches.
As storms track/develop southeastward amid steep boundary-layer
lapse rates, strengthening/expanding cold pools and a more
boundary-parallel component of the midlevel flow will promote
upscale growth into clusters and eventually a broken line into the
evening hours. As a result, damaging wind gusts will become an
increasing concern, before low-level static stability increases
(owing to nocturnal cooling) with southeastward extent.
..Weinman.. 04/09/2025
WUUS02 PTSDY2
SPC AC 081907
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0207 PM CDT Tue Apr 08 2025
Valid 101200Z - 111200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
OHIO VALLEY...MID-MISSISSIPPI VALLEY...AND INTO THE MID-SOUTH...
...SUMMARY...
Isolated severe storms capable of producing large hail and locally
damaging gusts will be possible from the Lower Ohio River Valley to
the Mid-Mississippi Valley and the Mid-South.
...Synopsis and Discussion...
A mid-level trough will amplify across the eastern CONUS on Thursday
with very cold mid-level temperatures (-22 to -26C at 500mb)
expected from the Great Lakes to the Mid-South. These cold
temperatures aloft will result in steep mid-level lapse rates which
will support weak to potentially moderate instability by
early-afternoon. Unidirectional flow, strengthening with height,
will support storm organization including updraft rotation. Overall,
the dry airmass, and thus relatively weak instability, should limit
a greater threat. However, cold temperatures aloft and forecast
soundings showing a deeply mixed boundary layer will support the
potential for some large hail and damaging wind gusts.
The greatest threat for stronger supercells will exist along the
cold front during peak heating (likely eastern Arkansas to northern
Alabama and southern Tennessee) where better moisture/instability
should be present. Despite a drier airmass farther north and east,
the coldest air aloft will advect over this region and could support
a threat as far northeast as far southern Ohio.
..Bentley.. 04/08/2025
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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