Cooler with breezy west winds can be expected through this evening. Winds turn offshore by Thursday, becoming stronger for the coastal slopes into the western valleys. The winds will bring cooler conditions across the mountains and deserts with slightly warmer conditions west of the mountains. Offshore winds will continue through the weekend with a chance of precipitation for some areas by Sunday into next Monday. A weak ridge will move over the region by early next week, bringing drier weather.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
A trough continues to push over Northern California today. This has contributed to a deeper marine layer that is taking its time clearing out this afternoon. Some areas near the beaches will be partially cloudy into the afternoon, but clouds will be expected to move back into the coastal areas and further into the inland valleys overnight into Thursday morning. If any fog forms, it will be over higher terrain. The troughing pattern will also bring elevated west winds across the mountains and deserts through this evening. Highest winds can be expected over the northern portion of our forecast area with mountain winds gusting near 35-50 MPH, while desert areas see winds closer to 25-40 MPH.
The trough will move inland over the Great Basin, stalling Thursday into Friday. This will bring northerly flow aloft, where winds will change to an offshore pattern by Thursday morning. North winds will funnel into the valleys and portions of the coast. Nbm 75th percentile winds show gusts primarily near 20-40 MPH across much of this region. Areas near the foothills show winds closer to 40-50 MPH, locally higher below the Cajon Pass. Winds look to weaken some by Thursday night, then ramp up again Friday morning.
The low pressure system associated with the longwave trough will become cut off from the system, and meander southwestward, eventually over northern Baja California. Since we will remain on the west and north side of the low, offshore winds will continue over the region through the weekend , potentially into early next week. Strongest and most widespread winds look to occur sometime around Saturday, when the pressure gradient is strongest. The low will be able to pull in some moisture from Mexico, potentially some light precipitation for the lower deserts into the mountains. The position of the low is still unresolved in the models, where a track too far to the south would bring mostly dry weather. Nbm chances increase near 15-30% by late Saturday night through Monday afternoon across these regions, even west of the mountains. Model ensembles do show light precip amounts, but these will be subject to change as we get closer in time. After the low departs, high pressure off the coast will begin to move over the area, with sunnier and drier weather.
041730z. Coast/Valleys, Low clouds with bases varying from 1000- 2000 ft MSL are currently extending about 15-20 miles into San Diego/Orange Counties. Scatter out 18-19Z, but low clouds will move back inland early this evening (00-03Z for San Diego County and 02- 05Z for Orange County). Clouds spread further inland overnight to include the western and southern Inland Empire. Bases will be similar, with some vis reductions for elevated inland valleys including the Inland Empire. Clouds clear early Thursday around 13- 16Z as winds turn northerly.
Mountains/Deserts, VFR conditions expected through the period. Westerly winds becoming strong through mountain passes, along desert slopes, and into the deserts after 03Z Thu. Gusts generally 25-40 kts, with isolated gusts to 55 kts for wind-prone passes and slopes. Winds turn northerly and weaken for most areas after 12Z Thu. The exception is Coachella Valley TAF sites (KPSP, KTRM) where wind gusts (25-30 kts) will be more favored after the northerly shift.
Stronger northwest winds develop on Thursday and continue into the evening, generating choppy and hazardous conditions. A Small Craft Advisory contains the details. Otherwise, no additional hazardous marine conditions are expected through Sunday.
Ca, Wind Advisory from 6 PM this evening to 4 AM PST Thursday for Apple and Lucerne Valleys-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.
PZ, Small Craft Advisory from 1 PM to 10 PM PST Thursday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm.
Small Craft Advisory from 7 AM to 10 PM PST Thursday for Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.
