SPC Dec 25, 2025 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0644 AM CST Thu Dec 25 2025

Valid 251300Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE
CALIFORNIA COAST AND PORTIONS OF THE CENTRAL VALLEY...

...SUMMARY...
An isolated risk for severe gusts and localized wind damage, and
perhaps a brief tornado will be possible today along much of the
California Coast and portions of the Central Valley.

... California ...
Water-vapor imagery early this morning shows a mid-level low over
the eastern Pacific and a negative-tilt shortwave trough moving
northward along the northern CA and OR coast. An upstream mid-level
speed max and associated vorticity max will move cyclonically
through the base of the eastern Pacific low/trough and approach San
Francisco Bay and northern CA this evening and subsequently move
into eastern OR by early Friday morning.

Strong to locally severe thunderstorms mainly capable of a
severe-wind hazard will potentially continue on an isolated basis
this morning from the Central Valley/central coast and perhaps
include portions of southern CA. The low CAPE/high shear
environment will potentially support strong/locally severe
convection contingent on sufficient updraft development. Forecast
low-level hodographs will remain sufficiently enlarged to yield a
low risk for a brief tornado across much of the Marginal Risk (level
1 of 5) area. By this afternoon, model guidance indicates low-level
flow will weaken before re-intensifying towards evening in
association with the arrival of the next speed max. A mix of linear
bands and cellular convective structures may continue to pose an
intermittent risk for isolated damaging gusts and perhaps a brief
tornado into tonight.

..Smith/Weinman.. 12/25/2025


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SPC Dec 25, 2025 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1137 PM CST Wed Dec 24 2025

Valid 251200Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE
CALIFORNIA COAST AND PORTIONS OF THE CENTRAL VALLEY...

...SUMMARY...
Thunderstorms with potential to produce marginally severe wind gusts
and perhaps a brief tornado will be possible on Thursday along much
of the California Coast and portions of the Central Valley.

... Synopsis ...

A highly amplified pattern will persist across the US as a deep
trough over the eastern Pacific is maintained and a ridge builds
over the central US. A series of embedded shortwave troughs within
the eastern Pacific trough will impact the West Coast on Christmas
and Christmas night.

... California ...

The first of these shortwave troughs will be moving across the
region at the start of the forecast period, bringing with it a band
of strongly forced convection, likely located across portions of the
central coast of California into the Central Valley. As the
shortwave trough takes on an increasingly negative tilt, a 50-60
knot southerly low-level jet will be maintained allowing for
sufficient low-level theta-e advection to support a modest 100-300
J/kg of surface-based CAPE. As the convective band interacts with
this strong low-level kinematic field, gusty/damaging convective
winds may be realized at the surface, particularly with the stronger
convective elements. Forecast low-level hodographs ahead of this
convective line feature sufficient low-level curvature to support a
brief tornado should any convective element realize true
surface-based buoyancy. As the morning progresses, the
aforementioned shortwave trough will lift north then northwest
within the broader cyclonic flow across the eastern Pacific whereas
the band of convection slowly advances south and east. By midday,
the low-level wind fields should weaken sufficiently in response to
the departing shortwave trough to reduce the potential of damaging
winds/tornadoes across far southern California.

By mid-afternoon, another shortwave trough will approach the central
and northern California coast. In response, the low-level wind
fields will once again strengthen, albeit perhaps not to the extent
as with the morning wave. Another band or bands of strongly forced
convection are expected to develop across the eastern Pacific and
approach coastal areas of central California after 00Z (4 PM PT). As
was the case with the morning convection, the strongest convective
elements may be capable of mixing down the stronger winds aloft
resulting in the potential for isolated strong thunderstorm winds.

..Marsh/Squitieri.. 12/25/2025


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SPC Dec 25, 2025 0100 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 0100Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0654 PM CST Wed Dec 24 2025

Valid 250100Z - 251200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ALONG MUCH OF
THE CALIFORNIA COAST AND PORTIONS OF THE CENTRAL VALLEY...

...SUMMARY...
An isolated risk for severe/damaging gusts and perhaps a brief
tornado will exist through tonight along much of the California
Coast and portions of the Central Valley.

... 01Z Update ...

Multiple bands of convection look likely this evening into the early
morning hours as a deepening surface low approaches the California
coast. The strongest convective elements within this first band,
currently approaching the San Francisco Bay area, will be capable of
producing gusty winds as it moves inland.

Wind fields will strengthen overnight in response to the approaching
low. This will maintain sufficient low-level theta-e advection to
support modest low-level instability through Christmas morning.
Numerical guidance this evening indicates a more intense band of
convection will approach the central and northern California coast
in the 08-12Z (12-4AM PT) window, quickly moving into northern
portions of the Central Valley. Given the modest instability and
strong wind fields, isolated strong wind gusts and a brief tornado
will be possible overnight, especially along the coast.

Elsewhere along the California coast, low-level moist advection will
persist through the night supporting localized convective
development. For the same reasons listed above, an isolated strong
wind gust or brief tornado would be possible with these convective
elements.

... Central Valley ...

Thunderstorms have developed this afternoon across portions of the
Central Valley near Sacramento. Surface-based instability around 500
J/kg within a strongly sheared environment will support an isolated
wind threat. Should convective elements become more cellular, the
low-level wind fields would support a brief tornado, especially in
areas where surface-based instability can be realized. This activity
will lift generally northward across the Central Valley through this
evening.

..Marsh.. 12/25/2025


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SPC Dec 24, 2025 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1153 PM CST Tue Dec 23 2025

Valid 241200Z - 251200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS COASTAL
CALIFORNIA AND THE CENTRAL VALLEY...

...SUMMARY...
Thunderstorms with marginally severe wind gusts, small hail and
potentially a brief tornado will be possible from Wednesday into
Wednesday night along parts of the California coast, and inland
across the San Joaquin Valley.

... Synopsis ...

A high-amplitude midlevel pattern will persist on Wednesday,
characterized by a deep trough across the eastern Pacific and a
building ridge across the Plains. This pattern will maintain a broad
belt of intense cyclonic flow across California into the Interior
West.

Throughout the day, an initial shortwave trough will continue
lifting northeast from the eastern Pacific into the Pacific
Northwest, while the attendant surface low lifts more northward
along the coast toward Washington. Late on Wednesday a second, more
potent trough will approach central and northern California --
primarily after dark. This setup will facilitate a prolonged period
rain and embedded thunderstorms across California and portions of
the Interior West into Thursday.

... California Coast ...

Strong ascent and strengthening onshore flow will aid in modest
destabilization Wednesday morning ahead of a surface cold front. An
ongoing band of convection is expected across the central and
southern coastal areas associated with the strongly forced ascent
along the advancing cold front. Given the presence of a strong
low-level jet (locally exceeding 50 knots at 1 km AGL), there is a
risk that these strong winds will mix to the surface within the
strongest convection resulting in damaging wind gusts. Forecast
soundings across the area do maintain some low-level curvature ahead
of the convective line, such that any convective element able to
interact with true surface-based buoyancy would have the potential
for a brief tornado.

In the wake of the morning convection, a secondary surface low will
intensify during the afternoon and overnight as it approaches the
northern California coast. This will likely trigger another round or
two of broken, low-topped convection along a second cold front.
Despite weaker instability than with the morning convection, the
strength of the wind fields would suggest an ongoing risk for
isolated wind damage as this convection moves inland.

... Central Valley ...

Cold midlevel temperatures and increasing height falls will
overspread surface dewpoints in the 40s to perhaps low 50s. Although
buoyancy will remain modest (MUCAPE at or below 500 J/kg), the
presence of a powerful midlevel jet in excess of 100 knots will
support long hodographs. This combination of modest instability and
large/long hodographs may support a threat for semi-organized
convection, including some potential for supercells. The strongest
storms will be capable of producing damaging gusts, hail, and a
brief tornado before the convection shifts east into the higher
terrain and weakens.

..Marsh/Squitieri.. 12/24/2025


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