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SPC Dec 20, 2023 2000 UTC Day 1 Convective Outlook

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SPC 2000Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0148 PM CST Wed Dec 20 2023

Valid 202000Z - 211200Z


Isolated thunderstorms remain possible across parts of
southern/central California and over portions of the Southwest.
Severe weather is not expected.

...20Z Update...
A band of precipitation well east of an upper low over the eastern
Pacific will continue to move slowly eastward across parts of
coastal central/southern CA this afternoon through tonight. Even
though surface temperatures ahead of this band have warmed more than
most guidance forecast across coastal portions of Santa
Barbara/Ventura counties, modest lapse rates aloft have hindered CG
lightning flashes thus far.

Nearly unidirectional southerly winds shown on recent VWPs from KVBX
and KVTX will continue to limit low/mid-level directional shear, and
should hinder potential for greater updraft organization amid weak
instability (MLCAPE generally less than 500 J/kg). While isolated
strong/gusty convective winds may still occur given the background
wind field, overall severe potential still appears low.

Isolated thunderstorms will also remain possible this afternoon and
early evening across parts of eastern AZ into NM in association with
a weak mid-level shortwave trough.

..Gleason.. 12/20/2023

.PREV DISCUSSION... /ISSUED 1025 AM CST Wed Dec 20 2023/

Low-amplitude ridging aloft will prevail across much of the country
today, as eastern U.S. troughing continues to slowly depart the
Northeast.  The main feature of interest with respect to convective
potential remains an upper low off the coast of California, which
will continue moving slowly southward.

Within the warm conveyor region of this system, and just ahead of a
weak surface front moving onshore, a disorganized band of convection
is indicated -- the strongest portion of which will gradually move
onshore over San Luis Obispo and Santa Barbara Counties over the
next few hours.  Ahead of this band, onshore instability remains
very weak and low-topped -- as evidenced by the overall lack of
lightning.  This, combined with weak low-level shear precludes any
appreciable risk for severe weather, though gusty winds may
accompany any stronger convective elements.

Elsewhere, sporadic lightning will continue across portions of the 
Southwest, in conjunction with a weaker mid-level disturbance moving
slowly eastward across the Four Corners states.  Thunderstorms are
not expected across the remainder of the U.S., where surface high
pressure and accompanying cool/stable conditions prevail.

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