Low clouds and patchy fog rapidly clearing out this morning as weak to locally moderate Santa Ana winds pick up. Offshore winds weaken Tuesday for warmer and drier weather with far less marine layer cloud coverage. Chances increase for another round of weak to moderate Santa Ana winds late Wednesday into Friday, peaking Thursday. Gradual warming Thursday into next weekend with highs near seasonal normals.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Morning update,
On the heels of the inside sliding upper trough now ejecting into the Great Plains, a 1032 mb surface high pressure has pushed through the Great Basin, establishing our offshore pressure gradient with weak to moderate Santa Ana winds already in place observed primarily through mountain passes where wind gusts of 30-50 mph have already occurred. The offshore flow has resulted in an early departure of the marine layer, with a few lingering patches of low clouds/inland fog set to clear out over the next hour or so.
From previous discussion,
Northeast to east winds are forecast to peak late this morning into the afternoon with gusts 30-45 mph below the passes, canyons, and near the foothills, with isolated gusts to 50 mph near the base of the Cajon Pass. Very weak ridging behind the departing trough and downsloping winds will lead to warming west of the mountains, where highs will be near to around 3 degrees above normal, but cooling across the mountains and deserts as cooler air moves in from the north. Santa Ana winds weaken tonight, turning back onshore by Tuesday morning. This will likely allow marine layer low clouds and fog to return to the coastal areas tonight. With the return of onshore flow and a trough beginning to drop down from the north, Tuesday will be slightly cooler with high temperatures near to slightly below normal.
Much like the system today, ensembles have completely trended towards an inside slider track with the next trough Wednesday to Thursday. While some ensemble members are still showing very light precipitation, it would be more in the form of drizzle from a deepening marine layer Wednesday morning. Rain/mountain snow have been removed from the forecast with chances of measurable precipitation now less than 10%. Disappointing but not surprising. Onshore flow will strengthen ahead of the trough Tuesday, then as it passes in an almost identical track as this morning, another round of gusty Santa Ana winds develops behind it on Wednesday. Winds are forecast to peak on Thursday when there is around a 30% chance of a weak to moderate event. Offshore flow will likely continue into at least Saturday morning, gradually weakening each day. Upper level ridging slowly builds in from the west along with the offshore flow for gradual warming and drying along with mostly clear skies for Thursday into early next week with highs warming to as much as 5-10 degrees above normal by Monday.
011615z. Coasts/Valleys, Localized areas of low clouds in western valleys based 1800-2400 feet MSL with inland vis 1-5SM will prevail through 18Z. Patchy low clouds based around 1200-1800 feet MSL will develop in coastal areas after 06Z into Tuesday. Offshore northeast winds 20-30kts with locally higher gusts will continue in foothills this morning and spread into parts of inland valleys after 17Z. These will continue through the afternoon, diminishing after 02Z. Otherwise, mostly clear and VFR conditions will prevail today and tonight.
.Mountains/Deserts, VFR conditions through the period. Gusty northeast surface winds on the coastal slopes of the mountains today exceeding 35kts at times. Mod up/down drafts possible in the vicinity of the mountain peaks. Localized areas of BLDU possible. Winds diminish after 06z Tue.
No hazardous marine conditions are expected today through Friday.
Ca, None. PZ, None.
