RSS Mesoscale Discussions from Storm Prediction Center
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0145 PM CST Tue Dec 23 2025
Valid 232000Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
COASTAL CALIFORNIA...
...SUMMARY...
An isolated threat for severe/damaging gusts and perhaps a brief
tornado may develop late tonight/early Wednesday morning across
parts of coastal California.
...20Z Update...
Relatively minor adjustments to the general thunder forecast were
made based on the latest observations and model guidance. The
remainder of the forecast remains unchanged. See the previous
discussion for additional information.
..Wendt.. 12/23/2025
.PREV DISCUSSION... /ISSUED 1020 AM CST Tue Dec 23 2025/
...California...
Within large-scale upper troughing over the eastern Pacific, an
embedded mid-level shortwave trough will move quickly eastward and
approach the CA Coast late tonight/early Wednesday morning. A
corresponding strengthening and increase in the flow through much of
the troposphere is anticipated late in the period, with a surface
low also forecast to deepen along/near the coast of northern CA. A
cold front attendant to this surface low will sweep quickly
eastward, and should be approaching/onshore across parts of coastal
northern/central CA by 12Z early Wednesday morning. Current
expectations are for the thermodynamic profile to remain mostly
saturated, with poor lapse rates generally limiting instability.
Even so, it appears that a gradual increase in low-level moisture
ahead of the cold front and slightly cooling mid-level temperatures
with the approach of the shortwave trough may support weak but
sufficient MUCAPE for an organized band of low-topped thunderstorms
late tonight.
Most guidance suggests this convection will not impact parts of
coastal CA until after 24/06Z, and there is still significant
uncertainty whether enough boundary-layer instability will be
present to support surface-based convection. There is also a signal
for pre-frontal convection in the low-level warm advection regime
across parts of central into coastal southern CA. Given the strength
of the low/mid-level flow forecast, and related strong
low-level/deep-layer shear, it appears that convectively enhanced
winds may be capable of reaching severe levels and producing damage
on an isolated basis even if instability remains minimal. A brief
tornado may also occur if convection can become truly surface based,
as effective SRH will be enhanced by a 50-70 kt southerly low-level
jet. Based on latest guidance trends, the Marginal Risk has been
expanded southward along the coast to include more of
central/southern CA. This isolated severe threat is expected to
continue beyond 12Z Wednesday into the Day 2 period.
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SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0122 PM CST Tue Dec 23 2025
Valid 251200Z - 261200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
COASTAL CALIFORNIA...
...SUMMARY...
Thunderstorms with marginally severe wind gusts and perhaps a brief
tornado, will be possible on Thursday along parts of the central and
southern California Coast.
...California...
Large-scale mid-level troughing is forecast to persist across the CA
coast and move onshore Thursday and Thursday night. Within the
broader trough, several embedded impulses will move onshore within
strong southwesterly mid-level flow. One of these stronger impulses
will start the day moving onshore over northern CA before quickly
lifting north into southern OR. A strong surface low and cold front
associated with this impulse will move quickly toward the coast
prior to 12z Thursday. A band of low-topped storms along the front
may be ongoing at the start of the forecast period, and persist for
a few hours Thursday morning. Confidence in sufficient buoyancy for
a sustained severe threat farther inland is low. Still, strong low
to mid-level flow and modestly steep low-level lapse rates could
support isolated severe wind gusts and perhaps a brief tornado early
along the coast.
The severe threat will likely shift southeastward toward southern CA
coast through the day as a second mid-level impulse and the main
core of the upper trough approach. Strong onshore flow and
persistent low-level moisture transport will allow for weak
destabilization near the coast during the afternoon and continuing
into the evening. 90+ kt of mid-level flow and locally enlarged
hodographs could allow for occasional stronger storms capable of
damaging gusts or a brief tornado despite the weak buoyancy.
..Lyons.. 12/23/2025
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