RSS Mesoscale Discussions from Storm Prediction Center
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1008 AM CST Mon Dec 22 2025
Valid 221630Z - 231200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Severe thunderstorms are not expected today.
...Synopsis...
A pronounced midlevel shortwave trough and associated baroclinic
zone will move across the WA coast later this afternoon.
Low-midlevel lapse rates will contribute to weak buoyancy of
sufficient depth (through -20 C at the equilibrium level) for charge
separation and isolated lightning flashes with low-topped convection
along and behind the front. Shallow, weakly rotating convection
will be possible near the WA coast per the KLGX VWP/hodograph, but
the threat for severe storms appears too limited to warrant an
outlook area. Farther south, the potential for isolated lightning
flashes will slowly wane through the day across the northern Sierra
Nevada, where weak buoyancy rooted above the surface will likewise
diminish.
Otherwise, a broad subtropical ridge (with unusually high
geopotential heights) covers the southern Plains/Gulf coast. An
embedded/weak midlevel trough will rotate slowly north-northwestward
around the periphery of the ridge, bringing weak ascent and an
associated moisture plume into south TX. Per the observed deepening
of the moist layer at BRO in the past 12 hours, pockets of surface
heating/destabilization could support isolated thunderstorm
development across south TX this afternoon.
..Thompson/Thornton.. 12/22/2025
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1112 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.
...Synopsis...
An expansive and unseasonably strong upper ridge will dominate the
mid and upper-level flow pattern across the CONUS Day2/Tuesday. As
the ridge intensifies, troughing on the flanks of the ridge will
also strengthen. The western most trough, and a mid-level shortwave
trough embedded within it will likely reach the central and northern
CA coastal areas late Tuesday night. Strong ascent and flow aloft
will support a deepening surface low which will support onshore flow
and some thunderstorm potential over much of coastal CA/OR.
...West Coast...
As the upper trough deepens over the West Coast, strong onshore flow
will develop and support inland transport of low-level moisture
across much of coast and the CA central Valley. Cooling mid-level
temperatures and strong ascent associated with the embedded
shortwave will overspread this air mass contributing to weak
destabilization late Tuesday through early Wednesday. Low-topped
convection, capable of occasional lightning, is expected to increase
in coverage overnight. While a stronger storm is possible,
especially along and ahead of the surface cold front, the scant
buoyancy and overnight timing suggest severe potential is very low.
Elsewhere, moisture advection is likely over parts of the southern
Plains and far south TX beneath the upper ridge as the surface
reflection shifts eastward. Despite persistent southerly flow and
increasing surface dewpoints, little to no ascent and warm mid-level
temperatures should preclude thunderstorm development outside of far
south TX.
..Lyons.. 12/22/2025
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