Scattered sprinkles and light showers tonight. The marine layer will deepen and spread far inland tonight, bringing patchy drizzle Wednesday morning. Cooler Wednesday with stronger southwest to west winds in the mountains and deserts. Warmer Thursday and Friday with weak offshore flow. A low pressure system moving inland to the north will bring cooler and breezy conditions for the weekend, followed by warming and another round of offshore flow early next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, The upper level low remains off the coast of So Cal this evening. A band of light showers and even a recently observed lightning strike near Long Beach has developed on the northeast side of the low, though due to a very dry subcloud layer any precipitation accumulation has been limited to a couple hundredths of an inch. The low will lift north and slightly eastward overnight, with any lingering mid- level instability and better dynamics shifting north of our area. The 00Z KNKX sounding shows the marine inversion based near 1200 ft MSL. The marine layer will deepen overnight as the upper low moves closer, but not convinced it will deepen enough to produce any drizzle tonight.
The low moves east across the region during the day Wednesday. This will bring significant cooling and gusty southwest to west winds in the mountains and deserts. Highs Wednesday will be as much as 10-15 degrees lower than today across the mountains, valleys, and high desert, and around 5 degrees lower for the low deserts and coastal areas. Winds will begin to strengthen Wednesday morning across the mountain ridges and upper desert mountain slopes, spreading into the passes and deserts Wednesday afternoon and evening with peak gusts of 35-45 mph, locally up to 55 mph below the passes. The low begins to move off to the east Wednesday night into Thursday morning, and winds will begin to weaken during that time. The marine layer will deepen further Wednesday night, with perhaps a better chance of drizzle west of the mountains.
Weak troughing lingers across the region on Thursday, and while mid-level winds turn northerly, weak onshore pressure gradients remain through the day, turning very weakly offshore to the north Thursday night into Friday morning. Overall this will lead to around 5 degrees of warming Thursday with highs generally a few degrees below normal.
Previous discussion, Ridging amplifies into Friday, and the mini warm-up will peak Friday afternoon with high temperatures around 5 degrees above average away from the immediate coast. The ridge will start to flatten and move off to the east Saturday as a large trough drops from the northwest. Model agreement is pretty good, with this remaining fairly well to our north, but this will lead to cooling temperatures this weekend and locally breezy winds (most likely lee mountain foothills and deserts again), as well as the marine layer deepening again. A few global ensemble members still have light showers west of the mountains, but the large majority are dry.
Some uncertainty with respect to the pattern next week, but some form of ridging is more likely, which will bring warming temperatures again, possibly to well above average.
220330z, Coast/Valleys, Low clouds based 1000-1500 ft MSL currently developing along the San Diego County coastline. Coverage expanding to include most of the coastal basin overnight with bases continually rising to above 2000 ft MSL after 12Z Wed. Scatter out 17-19Z. Low clouds based above 2000 ft MSL return early (00-03Z Thu) for San Diego County and along coastal slopes of the mtns. Slowly filling to cover the rest of the coastal basin overnight.
Otherwise, SCT-BKN clouds 12000-22000 feet MSL with VFR conditions through the TAF period. Strengthening west winds through Wed morning. Gusts 30-40 kts along and downwind of eastern facing mtn slopes after 18Z. Gusts to 50 kts through the most wind-prone passes.
No hazardous marine conditions are expected through Sunday.
Ca, Wind Advisory from 10 AM Wednesday to midnight PDT Wednesday night for San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
