Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0626 AM CST Mon Nov 25 2024
Valid 251300Z - 261200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
No severe-thunderstorm areas are forecast through tonight.
...Synopsis/Discussion...
A progressive, lower-amplitude pattern will prevail across the CONUS
this period, compared to the preceding week. A small cyclone now
centered over the southern SK/MB border area is forecast to
accelerate slightly and elongate southeastward, reaching that part
of ON just north of the MN border by 12Z tomorrow. As this occurs,
a basal shortwave trough -- apparent in moisture-channel imagery
from eastern SD to western CO -- should move eastward. This trough
will cross the mid/upper Mississippi Valley in the 21-03Z time
frame, then become negatively tilted, reaching Georgian Bay,
southern ON, and Lake Erie by 12Z.
The associated surface frontal-wave low was analyzed at 11Z from a
low over northern IL, southwestward near STL, FYV and ADM, to a weak
low near HOB. By 00Z, the main/northern low should reach eastern
Lower MI, with cold front across western parts of OH/KY/TN, northern
parts of LA/MS, and the TX Gulf Coastal Plain. By 12Z, the cold
front should extend from eastern PA across western parts of VA/NC,
northern GA/AL, southern MS/LA, and across the northwestern Gulf
shelf waters to near BRO.
Farther west, another mid/upper-level cyclone was centered over
Pacific waters west of OR, near 44N130W. This feature is expected
to devolve to an open-wave, positively tilted trough as it
approaches the coast today. The trough should cross the coast
between the Olympic Peninsula and northwestern CA obliquely, from
north-south, from 00Z to 12Z. Preceding the trough, DCVA/cooling in
midlevels will steepen lapse rates and support potential for
isolated thunderstorms, particularly over the relatively moist
Pacific boundary layer near the coast.
...Lower Mississippi to Tennessee Valleys...
Stronger deep-layer/large-scale lift will occur near the front in
the Ohio Valley to north-central Appalachians, but with poor
moisture return greatly limiting overall buoyancy. Somewhat greater
moisture -- but still in quite incompletely modified return-flow
trajectories with dewpoints generally low/mid 60s F in a shallow
layer -- is forecast in a narrow prefrontal corridor over the lower
Mississippi to Tennessee Valleys from late afternoon through this
evening. However, weak low/middle-level lapse rates (only barely
above moist adiabatic) will limit buoyancy there, with MLCAPE mostly
remaining under 500 J/kg. Briefly enlarged low-level hodographs
appear in some forecast soundings along or just east of the
prefrontal moist axis, especially from northern/eastern LA to
northern MS, suggesting non-zero storm-scale rotation potential for
any cell(s) that can mature fast enough before moving out of
surface-based inflow. At this time, severe risk appears too minimal
and conditional for an outlook. However, the scenario will be
revisited for evidence of greater unconditional potential, in
succeeding outlook cycles.
..Edwards/Leitman.. 11/25/2024
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