SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0130 PM CST Thu Jan 28 2021 Valid 282000Z - 291200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Scattered thunderstorm activity is possible, mainly near the coast and coastal ranges, from central California this evening into the vicinity of the Los Angeles Basin by 4 AM PST Saturday morning. ...20Z Outlook Update... The main surface front is now inland of coastal areas, as far south as Santa Barbara county, and surface cooling will overspread the remainder of southern California, into the lower Colorado Valley by late tonight. However, latest NAM and Rapid Refresh forecast soundings indicate that thermodynamic profiles supportive of convection capable of producing lightning will probably remain confined to beneath the mid-level cold core (including 500 mb temps at or below -28 to -30C). As of 20Z, across and to the south/east of the San Francisco Bay region, this is still mostly well offshore. Some convective development has been evident along and west of the northern coastal ranges, west through north of Ukiah. With additional heating this afternoon, some of these cells may deepen through sufficiently cold layers to produce lightning. Also, thin spots in the overcast are contributing to at least very weak boundary-layer destabilization across parts of the Sacramento Valley. With further breaks, and additional insolation, the development of a couple of thunderstorms may still not be out of the question late this afternoon. Otherwise, the primary risk for thunderstorm development appears to be late this evening and overnight along the coast and coastal ranges near and south of San Francisco Bay, perhaps as far south as the Los Angeles Basin by 12Z Friday, as the leading edge of the colder mid-level air advances southeastward. ..Kerr.. 01/28/2021 .PREV DISCUSSION... /ISSUED 1015 AM CST Thu Jan 28 2021/ ...CA... No changes have been made to the ongoing forecast. An upper trough is currently off the CA coast, and will spread inland through the afternoon and night. Cold temperatures aloft, steepening lapse rates, and large scale forcing will result in widespread showers across much of CA, with a few convective elements occasionally reaching sufficient depth to produce lightning. No severe storms are forecast.
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