RSS Mesoscale Discussions from Storm Prediction Center
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1121 PM CST Sun Dec 21 2025
Valid 221200Z - 231200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Severe thunderstorms are not forecast today.
...Discussion...
Midlevel short-wave trough, off the Pacific Northwest coast, is
forecast to advance inland around 23/00z before deamplifying as it
ejects into southwest Canada by the end of the period. Associated
surface front will also progress inland around 23/00z, and cooling
lower tropospheric profiles should lead to weak buoyancy along the
WA/OR coast. Low-topped convection may generate a flash or two of
lightning, but thunderstorms should otherwise remain quite sparse.
Late-evening water-vapor imagery depicts a weak short-wave trough
over northeast Mexico, lifting north in line with latest model
guidance. Deep southeasterly flow across south TX will maintain
moist profiles that should exhibit modest SBCAPE by late afternoon.
Forecast soundings also suggest deep-layer shear will remain quite
weak, and any convection that evolves across this region should
remain below severe levels.
..Darrow/Squitieri.. 12/22/2025
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SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1233 AM CST Mon Dec 22 2025
Valid 231200Z - 241200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Organized severe thunderstorms are not currently forecast across the
contiguous United States on Tuesday or Tuesday night.
...California...
An upper trough over the eastern Pacific will approach the West
Coast on Tuesday. A mid-level shortwave trough embedded within the
larger-scale trough will likely reach the central and northern CA
coastal areas late Tuesday night. A surface low will develop and
migrate northeast reaching the OR-CA border by early Wednesday
morning. Flow will increase during the period as a 100-kt 500-mb
jet impinges on the central coastal areas of CA. Yet, only scant
instability is currently progged. This meager buoyancy will
generally focus near the coast but sporadic pockets will probably
develop farther inland over the central valleys late Tuesday night.
Low-topped convective showers and isolated thunderstorms will
gradually increase in coverage coincident with increased forcing for
ascent and instability. Given the dearth of buoyancy forecast, will
preclude the introduction of low-severe probabilities.
Elsewhere, quiescent conditions will prevail across the Lower 48.
..Smith.. 12/22/2025
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SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0228 AM CST Mon Dec 22 2025
Valid 241200Z - 251200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
CENTRAL AND SOUTHERN COASTAL CALIFORNIA AND PARTS OF THE CALIFORNIA
CENTRAL VALLEY...
...SUMMARY...
Isolated strong to locally severe thunderstorms are possible on
Wednesday and Wednesday night across portions of California.
...California...
An upper trough over the eastern Pacific and upper ridge over the
Great Plains will maintain a belt of strong to intense cyclonic flow
across CA north-northeastward into the Interior West. A lead
shortwave trough will move from the OR/CA border northward into WA
during the day, while an upstream disturbance moves from the eastern
Pacific northeastward into central and northern CA after dark. A
prolonged period of scattered showers and episodic periods of
isolated thunderstorms are forecast across CA on Wednesday into
Wednesday night. Relatively cold mid-level temperatures (-20 to -24
deg C at 500 mb) will aid in the development of weak instability
during the afternoon across portions of the central valley.
Elongated hodographs coupled with the potential for a short-duration
period of modest surface-based destabilization could yield an
isolated risk for a couple of weakly rotating storms. A risk for
localized squalls moving inland near the immediate coast from parts
of southern into central CA may focus primarily late Wednesday into
Wednesday night ahead of the approaching disturbance.
Elsewhere, tranquil conditions will prevail across much of the
CONUS.
..Smith.. 12/22/2025
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