Cooling conditions and increased westerly winds on the desert mountain slopes into the deserts tomorrow into Thursday. The marine layer will deepen into Thursday, spreading low clouds and fog into the valleys. Periods of northeasterly Santa Ana winds and warmer conditions this weekend, with less marine layer low clouds and fog. Moisture from the east could bring some showers for Sunday and Monday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, New Aviation Discussion for the 18Z TAF package,
(today through Friday), A low pressure system will move inland into northern California today and through the Great Basin on Thursday. This will strengthen the onshore flow across southern California for today into tonight. West winds will strengthen for the mountains and deserts and be strongest for tonight with gusts to 45 mph and isolated gusts to 65 mph.
The marine layer is around 2000 feet deep early this morning with patchy low clouds extending inland into portions of the western valleys. The low clouds are expected to spread into portions of the inland valleys for tonight as the marine layer deepens. Fairly rapid clearing from north to south is expected on Thursday morning as offshore flow develops with gusty north winds.
The coast and valleys will cool a few degrees today. On Thursday, high temperatures for the deserts onto the desert slopes of the mountains will be around 10 degrees cooler than today while coastal areas will warm a few to around 5 degrees as the lower-level flow goes offshore.
Offshore flow will continue on Friday with gusty northeast winds along and below the coastal slopes of the mountains. High temperatures on Friday will cool slightly for inland areas with slight warming near the coast.
(Saturday through Tuesday), For the weekend, the center of a closed low pressure system will be somewhere over or offshore of northern Baja. Cluster analysis shows the solutions with greater chances for at least light precipitation for Sunday and Monday are those that are farther west with the center while those that are farther east are dry. The strength and placement of the stronger offshore winds for the weekend are also dependent on the placement of the upper low.
High temperatures will warm through the weekend with Sunday high temperatures as much as 8 to 12 degrees above average for coastal areas. As offshore flow weakens early next week, the coast and valleys will begin to cool while the deserts continue to slowly warm.
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.
