textproduct: San Diego

SYNOPSIS

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.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

Update: At this time, low clouds and fog have continued to struggle to reform and fill back in along the coastal areas this evening, with the only significant banding of clouds being located right along the stretch of beach from Camp Pendleton down to Cardiff by the Sea. This is partially due to weak offshore winds, which will continue to inhibit some of these low clouds and fog from forming throughout the night. There will be some patchy areas of dense fog likely forming along the immediate coastline going into the early morning hours, especially for San Diego County. The marine layer should continue to fill in northward and stretching about 5 to 10 miles inland, and depending on how (and where) this ends up developing will also determine how quickly it scatters out. A consensus of the high res models has everything clearing out by around 10 AM tomorrow. The forecast still remains on track with cooling through the weekend and into early next week, along with some possible drizzle for the coastal and inland areas by Monday, and then a large area of low pressure will slowly advance towards the region, with the possibility of some showers associated with this system to begin as early as Tuesday morning of next week, and then chances of precipitation increasing thereafter going into the latter half of next week as temperatures also continue on a cooling trend through then.

Previous discussion submitted at 114 PM:

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.

AVIATION

180430Z...Coast/Western Valleys...Low clouds based 500-900 ft MSL along the immediate coast will continue to reform and push into coastal San Diego County, and eventually northward into Orange County. Minor vis restrictions initially (2-5SM) will slowly worsen again as bases lower after 06Z with areas of dense FG becoming likely, especially along the immediate coastline. FG may expand to include Orange County after 06Z (40%) but coverage will become patchier with FG likely retreating from most land areas 12-15Z. Patchy FG through 18Z over coastal waters.

Otherwise...VFR conditions today and tonight. Elevated winds in the High Desert gusting 25-35 kts through 06Z Thu. These winds will increase again tomorrow, with similar

MARINE

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.

SKYWARN

Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.

SGX WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.