Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0148 PM CST Wed Dec 20 2023 Valid 202000Z - 211200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... 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/ ...Discussion... 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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