Cooler west of the mountains today and warmer inland. A low pressure system moving into California brings cooler and breezy conditions Monday through the middle of next week, along with a slight chance of precipitation Tuesday afternoon into Wednesday morning. Cool weather and breezy onshore flow persist for the remainder of the week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, New Aviation and Marine Discussion,
Scattered high clouds are lifting northeast across the region this evening well ahead of an upper level low off the Pacific Northwest coast. With the high cloud coverage, low clouds off the coast remain sparse. Patchy low clouds may develop over the coastal areas and far western valleys later this morning, clearing by mid-morning.
An upper level ridge currently near the Lower Colorado River Valley will shift slightly eastward and amplify over the Desert Southwest today, bringing warmer weather in the mountains and deserts. A stronger sea breeze today will help spread marine air into the coastal areas and valleys for some cooling. In general high temperatures will be around 3-8 degrees above normal today. The upper level low gradually drops south today and then moves towards the coast on Monday, bringing more widespread cooling with increasing southwest to west winds in the mountains and deserts. The marine layer will deepen with this approaching low, with more widespread low clouds tonight into Monday morning spreading into parts of the inland valleys.
A negatively tilted short wave associated with the upper low lifts across So Cal Tuesday afternoon and evening. We'll be on the tail end of this system with limited moisture to work with. The 00Z ensembles have trended drier with this trough with ensemble mean precipitation now down to a couple hundredths of an inch for the coastal areas and valleys. Chances of measurable precipitation (at least 0.01") range from around 50% along the LA County boarder and coastal mountain slopes to 30% in southern San Diego County, 25% in the high desert, and less than 10% in the low desert. Chances of 0.10" or more have decreased since yesterday, now down to around 5-25% for the mountains westward, highest near the LA County border and decreasing to the southeast. The bigger impact from this trough will be strong and gusty southwest to west winds in the mountains and deserts Tuesday afternoon through Tuesday night when local gusts to 55 mph are possible along the desert mountain slopes and through the passes. The main trough axis moves through by Wednesday morning, at which point winds will begin to weaken. Wednesday will be the coolest day of the week when highs will be around 5-10 degrees below normal away from the coast, and up to 3 degrees below normal near the coast.
Weak troughing remains across the Western US for the rest of the week, maintaining cool weather, a deep marine layer, and breezy conditions in the mountains and deserts. Another upper low may develop off the coast in the southern branch of the split flow and eventually make it towards So Cal late in the week, but there is still a lot of spread in the ensembles regarding the evolution of this pattern. If the low develops far enough west that it could pick up moisture before making it here we will have another chance at precipitation by early next week, but this pattern is generally low predictability so don't count on anything yet.
191130z, Mostly high clouds out there with a small patch of low clouds coming in at the very southern part of coastal San Diego County at 1000-1500ft MSL. There is a 40-60% chance of these low clouds reaching KSAN after 12Z and lasting through 17Z. Low clouds are expected to redevelop after 04Z Monday mainly along the coast with higher probabilities for coastal San Diego.
Increasing westerly to southwesterly winds across the desert slopes into the deserts this afternoon/evening near 20-30 kts.
Otherwise, VFR conditions expected through the TAF period.
No hazardous marine conditions are expected through Tuesday. Elevated onshore (northwesterly) wind gusts near 20-25 knots are possible Wednesday into Thursday.
Ca, None. PZ, None.
