Warm weather will continue across the region with patchy fog closer to the coast through Friday with gusty winds across the high desert today. A subtle cooling trend will occur over the weekend as high pressure weakens over the area, though temperatures will remain above normal. A low pressure system will bring increasing chances for rain by Tuesday, with heavier rain possible around the Christmas holiday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Low clouds and fog continue to be intermittent near the coastline, with a slow clearing trend observed on satellite this afternoon. The flattening of the ridge aloft will create a slightly stronger pressure gradient, where winds will be gusty near 30-40 MPH across the high desert through this afternoon. The hazy and foggy trend will continue through the afternoon before clouds begin to build back into the these areas early this evening, highest chance of fog again across coastal San Diego County. Models suggest clouds may dissipate before sunrise as weak offshore flow occurs over the region as well. This is all due to high pressure over the area increasing in strength. This will also bring greater warming across the region by Thursday, which will be the last very warm day for awhile. High temperatures will be close to 20 degrees above average by Thursday, where places like Borrego Springs, Big Bear, Alpine and Idyllwild may see record high temperatures for the day.
The high will weaken by Friday, with winds turning back onshore. This will bring a few degrees of cooling for areas west of the mountains with most of the mountain and desert areas remaining unchanged, where highs remaining 15 to 20 degrees above normal. The high will continue to push southward as a weak atmospheric river and trough to the north begin to move across Northern California and the Pacific Northwest. The high will continue to dominate our weather pattern through next Monday with night and morning low clouds near the coast and high temperatures well above normal. The lower deserts will still see highs in the lower 80s on Monday with plentiful 70s across the valleys and high desert.
The moisture plume and trough of low pressure to the north will move southward by the middle of the week, combining into a stronger and deeper area of low pressure. Nbm brings in chances for precipitation starting Tuesday into Tuesday night across the region, with more widespread precipitation expected by Wednesday and Christmas Day. The timing of this system still remains highly uncertain based on the nature of the ridge the departing ridge to the south and where exactly the area of low pressure sets up. It is definitely plausible that the low deepens enough to stay off to the west and north through Tuesday, which wouldn't bring any rain to the area until Wednesday. Though confidence in rain totals is low, there has been an upward trend in rainfall over the past couple of days. Heaviest rainfall is expected to be over the coastal basin. Chances for total rainfall over 2 inches ranges from 35-55% in Orange County and the Inland Empire, closer to 20-40% across San Diego County. As of now, model guidance points to later on Christmas Eve into Christmas Day seeing the heaviest precipitation. But if the system stalls at all or remains further off the coast, the heaviest rainfall may be pushed back in time where precip may continue into next Friday or beyond. Confidence continues to increase that bouts of heavy rainfall will lead to an increased flood and debris flow risk, as well as holiday travel disruptions for the entire region.
Areas of fog and low visibility (less than 1SM) returning late this evening and overnight as clouds lower again. Fog will likely become more patchy overnight and scatter out by mid morning Thursday.
Ca, None. PZ, None.
