ACUS01 KWNS 241952
SWODY1
SPC AC 241950
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0150 PM CST Wed Dec 24 2025
Valid 242000Z - 251200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
COASTAL CALIFORNIA AND PORTIONS OF THE CENTRAL VALLEY...
...SUMMARY...
An isolated risk for severe/damaging gusts and perhaps a brief
tornado will exist today into tonight along much of the California
Coast and portions of the Central Valley.
...20Z Update...
...Central/Northern California...
Water vapor imagery shows the shortwave trough already moving
inland. In the wake of this activity, visible satellite shows
potential for cloud cover to reduce within the Central Valley from
west to east. Some forecast soundings show destabilization is
possible by late afternoon. Given the southeast flow within the
Valley and strong flow aloft, a conditional threat for a marginal supercell/brief tornado could develop.
Greater confidence exists with activity later in the evening into
Thursday morning associated with a secondary, stronger shortwave
trough. Another narrow band of convection is expected ahead of this
shortwave and will impact parts of the central/northern California
Coast and eventually parts of the Central Valley as well. Isolated
damaging winds and a brief tornado would be possible with this
activity.
...Southern California...
A spatially limited threat for wind damage and a brief tornado will
exist for another few hours this afternoon. A low-topped band of
convection recently moved through much of the LA Basin and will
generally continue eastward. There may be a narrow sliver of
dewpoints near 60 F just east of this activity. Dewpoints closer to
San Diego are only in the upper 50s F, however. Strong wind shear at
low levels will maintain this marginal risk, though decreasing
buoyancy southward and inland should lead to a downward trend in
intensity.
..Wendt.. 12/24/2025
.PREV DISCUSSION... /ISSUED 1025 AM CST Wed Dec 24 2025/
...California...
A shallow band of pre-frontal convection may continue to pose a
threat for locally severe/damaging winds (especially across higher terrain/ridgetops) and perhaps a brief tornado this morning across
parts of coastal southern CA. This activity is being supported by
strong low-level warm advection and large-scale ascent associated
with an enhanced mid/upper-level jet. Current expectations are for
this activity to continue moving eastward through the afternoon
across the remainder of coastal southern CA in a strongly sheared
environment. However, various NAM/RAP forecast soundings across this
area suggest that even with low 60s surface dewpoints and
modest/filtered daytime heating, the overall severe threat will
likely remain isolated due to poor lapse rates aloft and limited
boundary-layer instability. Reference Mesoscale Discussion 2269 for
more details on the near-term severe threat across southern CA.
Additional rounds of convection are expected later this evening and
overnight into early Thursday morning over portions of
northern/central CA, as multiple mid-level shortwave troughs
embedded within persistent large-scale upper troughing over the
eastern Pacific overspread these areas. One such shortwave trough is
forecast to advance over coastal central CA and vicinity around
25/00-06Z this evening, with cool temperatures aloft (less than -20C
at 500 mb) supporting weak MUCAPE. Both low-level and deep-layer
shear are expected to gradually increase this evening as the
shortwave trough approaches, with some updraft organization
possible. Strong to locally severe winds and a brief tornado or two
appear possible with this activity, but uncertainty is still
substantial whether sufficient instability will be present to
support surface-based thunderstorms.
A stronger mid-level shortwave trough will move east-northeastward
from the eastern Pacific and approach the northern CA Coast by 12Z
Thursday morning, along with a deepening surface low and attendant
cold front. A 70-80+ kt mid-level jet will accompany this shortwave
trough, along with a 50-60 kt south-southwesterly low-level jet. A
broken band of low-topped thunderstorms will likely develop in
association with this shortwave trough along/ahead of the front, and
overspread coastal portions of northern/central CA late tonight
through early Thursday morning (25/06-12Z). A strongly sheared
environment and weak but sufficient MLCAPE may exist to support at
least an isolated threat for severe/damaging winds and a tornado or
two as this activity spreads inland through the end of the period.
Still, the overall severe threat should be tempered by the lack of
stronger instability.
Finally, some chance for low-topped/mini supercells may exist late
this afternoon/evening across parts of the Central Valley of CA. If
these thunderstorms can develop and be sustained, they could pose a
threat for both damaging winds and a brief tornado. But, confidence
in this scenario occurring remains rather low.
$$
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