Day 1 Severe Weather Outlook

Valid 042000Z – 051200Z


A few thunderstorms remain possible this afternoon into this evening
across parts of central and southern California into portions of the
southern Great Basin.

…20Z Outlook Update…
The latest Rapid Refresh, supported by satellite imagery, suggests
that the mid-level thermal trough is now mostly inland of the
central and southern California coast, with the -20 to -22 C 500 mb
cold core forecast to spread from the coastal ranges, between the
Los Angeles Basin and San Francisco Bay, across the San Joaquin
Valley and southern Sierra Nevada into portions of the Mojave Desert
through this evening. As insolation beneath the nose of the
mid-level dry slot contributes to mixed-layer CAPE increasing to
250-500 J/kg across the coastal ranges, the initiation of scattered
thunderstorms is expected, with subsequent advection/redevelopment
into the San Joaquin Valley possible through late afternoon.

Potential for thunderstorm development east of the southern Sierra
Nevada is becoming more unclear, but thunderstorm probabilities
appear to decrease across the Mojave Desert, and become increasingly
negligible as the mid-level cold core overspreads the southern Great
Basin later tonight.

..Kerr.. 12/04/2019

.PREV DISCUSSION… /ISSUED 1003 AM CST Wed Dec 04 2019/

Thunderstorm chances throughout the forecast period will be tied to
an advancing closed low near the central California coast. Cooling
aloft has promoted enough destabilization to result in isolated
lightning flashes in southwestern California this morning, and
lightning-producing convection should continue to develop/spread
eastward through the forecast period with eastward progress of the
upper low. Vertically veering wind profiles may result in brief
updraft rotation as convection approaches the coast and interacts
with locally backed (and terrain-altered) surface flow, though the
overall risk of any severe weather is isolated enough to preclude

Farther east, an anticyclone over the Deep South has kept deeper
moisture/buoyancy confined to the central Gulf of Mexico while
continental, dry air persists across much of the central U.S. This
will preclude any appreciable thunderstorm risk through 12Z


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