Periods of isolated light to locally moderate rain showers will continue into Wednesday, most likely for the Orange County coast and across San Diego county. Gusty west to northwest winds are expected for Wednesday evening into Thursday, strongest for the desert mountain slopes into the deserts. Santa Ana winds will quickly develop Thursday afternoon/evening and strengthen Friday through the weekend. Warm days west of the mountains can be expected Friday into early next week with cold nights in the deserts and any wind sheltered locations in the valleys and mountains.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Widespread mid to high cloud coverage is expected into Wednesday as a closed upper level low continues to move south today, before moving east into northern Baja tonight. The highest chances of precipitation this evening into Wednesday are across San Diego County, including the San Diego County desert. Any rainfall tonight into Wednesday should be light to locally moderate, with peak rainfall rates 0.10-0.35" per hour. Rates at the higher end of the that range are most likely to occur in San Diego county. Rainfall totals from tonight through Wednesday afternoon will range from 0.05- 0.35", with totals on the higher end of that range expected in far southern San Diego County. Snow will fall above 7,000 feet in the mountains, with very little if any sticking in the Riverside County mountains. Showers should become more localized to the mountain slopes of the Riverside and San Diego mountains by Wednesday afternoon with dry conditions expected to return by Wednesday night.
A fast-moving inside slider will move through the interior West Wednesday night into Thursday. Latest guidance has the track of this inside slider further south and west which has resulted in a significant increase in our wind forecast for Wednesday night into Thursday. Gusty westerly winds are expected for the mountains and deserts. Wind gusts for the desert mountain slopes will peak at around 50-70 mph (potentially locally higher in west wind favored locations) with gusts in the deserts peaking at 40-55 mph. As the upper level low settles over the Four Corners region Thursday afternoon/evening northerly offshore flow will quickly develop as high pressure aloft rapidly amplifies along the West Coast and cold air produces strong surface high pressure over the Great Basin. This initiates what looks like a prolonged period of offshore flow that will continue into next week at least.
Winds will become more northeasterly Friday through the weekend as the main driver of the Santa Anas becomes the pressure gradient between Southern California and the Intermountain West. Latest ensemble guidance has trended slightly stronger with Friday's winds but winds continue to look strongest and most widespread over the weekend when the surface high peaks in strength. Moderate to locally strong northeast winds look possible Friday through Sunday. There is some potential for moderate strength Santa Ana winds to continue into Monday, but chances decrease from 40-60% over the weekend to around 20-30% on Monday. Thankfully, due to all the rain we've received in December, fire weather conditions will likely only remain elevated due to gusty winds and minimum relative humidity falling to the teens. Fuel moisture will be above critical levels.
In addition to the gusty Santa Ana winds, high temperatures for the coast and valleys will reach the 70s to locally low 80s by early next week. Low temperatures in the deserts and wind sheltered locations in the valleys and mountains are expected to fall to the 30s and low 40s, even as low as the upper 20s in the High Desert. Based on the current forecast, the coldest mornings are looking to be Friday through Sunday. Overnight lows should increase slightly for early next week as the surface high weakens, resulting in less cold air advecting into our local deserts. From Friday onward, marine layer low clouds and fog are expected to be absent from coastal areas due to the dominate offshore flow.
061700z, ISO SHRA remains about 10 miles off the coast of San Diego County. Slight chance (10-20%) a SHRA approaches KSAN through 21z, briefly reducing CIGs near 1500-2500ft and VIS down to 3-6SM.
Otherwise, VFR conditions and FEW-SCT clouds near 4500-5500ft MSL over the coastal basin into the afternoon. An additional round of SHRA is possible after 02z Wednesday, likely starting off isolated in the SD County foothills, though a few showers could extend into the Inland Empire and Orange County. Greater SHRA activity possible in SD County after 16z Wed. Accompanying this precipitation is likely brief CIGs near 1500ft MSL and VIS reductions to 2-5SM in areas of -RA/RA.
Breezy northwest winds near 20 to 25 knots expected Wednesday night into Thursday morning near San Clemente Island. Otherwise, no hazardous marine conditions forecasted through this weekend.
Ca, High Wind Watch from Wednesday evening through Thursday evening for San Bernardino County Mountains.
High Wind Watch from Wednesday evening through Thursday afternoon for Riverside County Mountains-San Diego County Mountains-San Gorgonio Pass near Banning.
Wind Advisory from 8 PM Wednesday to 1 PM PST Thursday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts.
PZ, None.
