Weak offshore flow will continue today. Near to slightly above average temperatures expected through Monday, before below average conditions return for the middle of the week. Gradual warming for the end of the week, with cooler conditions next weekend. Patches of marine layer low clouds and fog will return to parts of the coastal waters today, with the potential for areas of dense fog. Low cloud coverage will become more widespread into the middle of the week. Areas of drizzle possible Wednesday for areas west of the mountains.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Weak high pressure aloft will continue to prevail over the area early this week, keeping temperatures near to slightly above average. Periods of weak offshore winds from the northeast to east will be present on the coastal slopes of the mountains, locally into the foothills, through Tuesday. The prevailing offshore flow will limit marine layer low cloud and fog coverage early this week. Any low clouds and fog that do develop will most likely occur over the coastal waters and near the coast with areas of dense fog possible.
A closed low that is currently west of Southern California will begin to slowly move east Monday and Tuesday. By Wednesday, the low is expected to quickly move east across Southern California. This will bring an increase in cloud coverage and cooler conditions. Westerly winds may become elevated over the mountains, locally into the deserts. By Wednesday, highs for inland locations are expected to be 7 to 12 degrees below average, with some mountain locations seeing highs 15 to 20 degrees below average. Rain chances associated with this system continue to look marginal. Chances of measurable rainfall occurring remain less than 10 percent, with the best chances for any accumulating rain on the coastal mountain slopes. Areas of patchy drizzle are possible west of the mountains on Wednesday, especially with the increase in onshore flow and rapid deepening of the marine layer.
As the low continues to move east weak ridging will set up again over Southern California for Thursday and Friday. This will bring a few degrees of warming, weak offshore flow, and a shallower marine layer. For next weekend, we're monitoring the potential for a deep trough of low pressure from the Gulf of Alaska to dig south into the US West Coast. Currently, most of the ensemble guidance keeps the low off the coast of the Pacific Northwest through next Saturday, which would keep us dry through then. By next Sunday, most ensemble guidance has the trough moving inland although there remain some differences in timing and amplitude of the trough. There is fairly good consensus that the track of the low will be more inland, making it less favorable for significant precipitation to occur. There are still some ensemble members showing light rain is possible, but more than likely the main impact from this system for our area of responsibility will be an uptick in winds over the mountains and into the deserts.
190900z. Coasts, A few stray patches of very low marine clouds (based 100-400 ft MSL) are off shore this morning. There is a slight chance (10%) for patchy FG from these clouds at the coast until 15z this morning. Better chance (35-45%) for low clouds and fog to develop along the coast after 09z Monday.
Valleys/Mountains/Deserts, VFR conditions continue through early Monday.
Patchy fog with visibilities likely under 1 SM possible over the waters this morning and could be more widespread Monday and Tuesday mornings. Otherwise, no hazardous marine conditions are expected through Thursday.
Ca, None. PZ, None.
