A low pressure system moving inland into Arizona will bring scattered showers this morning with the showers decreasing in the afternoon. There will be slow warming on Wednesday and greater warming on Thursday with a period of gusty Santa Ana winds with the stronger gusts to around 50 mph. Winds will weaken on Friday with another round of stronger and more widespread Santa Ana winds for next weekend, strongest on Saturday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
(today through Thursday), Scattered showers will move inland early this morning with the greatest coverage across San Diego County inland to the mountains. Those areas could receive an additional one-quarter to one-third inch with local amounts exceeding one-half inch. The showers are expected to diminish in the afternoon. High temperatures today will be a few degrees cooler for most areas. Wednesday will begin to warm with the greatest warming for the mountains and inland valleys.
Gusty northerly Santa Ana winds will develop Wednesday night, then become more widespread on Thursday morning before diminishing some in the afternoon. The stronger gusts are expected near and below the Cajon Pass and in the coastal foothills of the Santa Ana Mountains with stronger gusts to around 50 mph. More localized northerly winds will continue Thursday night diminishing early Friday. With those Santa Ana wind, there will be greater warming toward the coast on Thursday. Coastal areas will warm 10 to 15 degrees with warmest high temperatures for some inland coastal areas approaching 80.
(Friday through Monday), Lower level flow on Friday will go back weakly onshore for coastal areas in advance of a round of stronger and more widespread northeasterly Santa Ana winds for Friday night and Saturday, becoming more easterly for Saturday night and Sunday.
Ensemble output from the ECMWF shows this should be a stronger and longer duration event than for the Santa Ana winds on Thursday. ECMWF ensemble output for Ontario shows greatest support for a moderate strength event with smaller subsets supporting a weaker or a stronger event. About 20 percent of members have support for at least a brief period of stronger winds.
There is some spread in the timing for the onset of the winds on Friday night and the strength and duration of the winds for Saturday night and Sunday as the winds become more easterly. Northern areas should see the stronger winds on Saturday while the strength in portions of San Diego County may not be that much different on Saturday or Sunday as the winds transition for northeasterly to easterly. Winds should more noticeably weaken and decrease in coverage for Sunday night and Monday.
High temperatures on Friday should be cooler for coastal areas while some inland areas continue to warm. With the initial arrival of the Santa Ana winds on Saturday, the coast will warm while most inland areas will cool. Most areas will then warm on Sunday with warming continuing on Monday for inland areas while the coast begins to cool.
181015z, Coast/Valleys/Mountains, BKN-OVC 3000-5000 feet MSL obscuring higher terrain through 20Z. -SHRA would bring cigs down to 1200-2000 feet MSL and vis down to 2-5SM. Scatter out occurring from north to south and from coast to valleys after 18Z, with cigs and isolated -SHRA continuing in foothills and mountains into the afternoon. Clearing in higher mountains after 02Z, but clouds continuing in coastal basin 1500-2500 feet MSL overnight into Wednesday.
Deserts, SCT-BKN clouds 6000-10000 feet MSL with isold -SHRA this morning with gradual clearing after 20Z.
No hazardous marine weather conditions are expected through Friday.
Ca, NONE. PZ, NONE.