Temperatures peak today around 5 to 10 degrees above normal as weak high pressure passes by. Starting tomorrow, a cooling trend is expected with increasing onshore flow ahead of a low pressure system for the weekend. Light to moderate precipitation will fall across most of Southern California in two rounds, one on Saturday and one from Sunday into Monday. Additionally, elevated westerly winds are expected for the mountains and deserts from Thursday through the weekend. Seasonably warm and dry weather returns from next Tuesday through mid next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
With clear skies and weak ridging across the region, we can expect the warmest day of the week for most locations today. Temperatures will range from around 70 near the coast to the upper 90s in the lower deserts. 70s and 80s expected for inland valleys, High Desert, and lower elevations of the mountains.
By Thursday, the weak ridge will be pushed to the east by an incoming upper troughing pattern. High clouds will spread over the region starting early Thursday morning, which may disrupt marine layer cloud development. A cooling trend will commence with highs dropping by a few degrees both Thursday and Friday. Additionally, increased onshore flow will allow for afternoon/evening elevated west wind gusts around 35-45 mph for the mountains and deserts.
Further cooling is expected for the weekend along with widespread off-and-on precipitation and continued elevated west to southwest winds for the mountains and deserts. The precipitation will feature two main waves. The first wave is expected to pass over Southern California late Friday into early Saturday. Guidance has trended weaker and further north with this system. Therefore, QPF has decreased with less than a quarter of an inch for most of the coastal basin and almost none in the deserts through Saturday. However, modest instability may still produce an isolated thunderstorm or two for the coastal basin, which would locally enhance rainfall rates and totals.
The second wave will arrive on Sunday with precipitation lingering into early Monday. Most of the guidance is in agreement that this wave will be the stronger (and colder) of the two, but still expecting mostly light to moderate rainfall rates and totals. Overall, QPF for the weekend has trended downward with NBM probability of exceeding 0.5" now around 20-40% through the coastal basin and 40-70% for the mountains. Snow levels are still expected to slowly fall from 7500 feet to 6500 feet through the weekend.
There is some indication that a weak, tertiary shortwave may allow for light shower activity to linger through Monday. However, a large majority of the guidance brings a return of dry and seasonable weather from Tuesday through the middle of next week.
081615z, Mostly clear through the early evening hours. Coastal low clouds at 900-1400 feet MSL to redevelop after 06Z Thu in San Diego County and after 09Z Thu in Orange County. Clouds scattering 15-17Z. Brisk west to southwest winds 25-35 kts over the mtns/desert foothills into the deserts after 01Z Tue.
There will be occasional wind gusts exceeding 20 knots and locally choppy conditions in the vicinity of San Clemente Island tonight. There is a 20% chance of thunderstorms over the waters Friday night through Saturday. Otherwise, no hazardous marine conditions are expected through Sunday.
Ca, None. PZ, None.
