SPC AC 041950
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0150 PM CST Sun Dec 04 2022
Valid 042000Z - 051200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
The risk for thunderstorms appears negligible across much of the
U.S. this afternoon through tonight.
Orographic forcing along the western slopes of the northern Sierra
Nevada might still contribute to isolated convective development
vigorous enough to pose some risk for producing lightning. However,
in the wake of one perturbation pivoting around the periphery of the
offshore low, mid-levels are in the process of gradually warming
from southwest to northeast. Even with insolation this afternoon,
this will tend to limit further boundary-layer destabilization,
which remains negligible at this time.
Otherwise, widely scattered convection capable of producing
lightning remains possible near immediate coastal areas, mainly late
this evening into the overnight hours with the approach of the
remnant upstream cyclonic mid-level circulation.
A continued increase in low-level moisture may now be contributing
to weak conditional boundary-layer instability across southeastern
Arizona into adjacent portions of southwestern New Mexico. However,
VWP from Tucson indicates that low/mid-level wind fields have been
gradually veering through the day, in the wake of one weak
low-amplitude mid-level perturbation. And model output generally
suggests that forcing associated with any upstream perturbations
will be weaker and largely confined to areas near or south of the
international border late this afternoon into tonight.
.PREV DISCUSSION... /ISSUED 1010 AM CST Sun Dec 04 2022/
A mid/upper-level low west of the OR/CA border area will drift
towards the coast through early Monday. Bands of ascent associated
with embedded perturbations along with moderately steep lower-level
lapse rates and weak buoyancy will support potential for isolated
thunderstorms from the northern CA coast into the Sacramento Valley
through tonight. Small hail is possible in low-topped convection
along the immediate coast where buoyancy should be relatively
greater, but the bulk of strong mid/upper speed shear will exist
above the buoyancy profile owing to a pronounced inversion between
Weak elevated convection will remain possible across southeast AZ
and far southwest NM, within a persistent subtropical moisture
plume. Scant buoyancy might support sporadic lightning flashes.
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