Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
017 FXUS66 KSGX 050330 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 830 PM PDT Sat Oct 4 2025 .SYNOPSIS... Mild, near to below normal temperatures with little day to day change through Monday, followed by a gradual warming trend into the middle/latter part of next week. Daily marine layer clouds will likely make a comeback early Sunday morning, with more widespread low clouds next week. Periods of weak offshore winds overnight and in the mornings over mountain ridges and in the deserts will occur through early next week. There is the potential for tropical moisture to move into the area late in the week, bringing a slight chance of showers, most likely over the mountains but with the potential for more widespread activity. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .Evening Update... Patchy low clouds continue to develop offshore this evening. These will slowly increase in coverage overnight with some cloud cover lingering into the morning near the coast before clearing thereafter. Calm conditions will continue through the middle of the week. We continue to watch Tropical Storm Priscilla to the south. There remains great uncertainty on the exact track of this system. The synoptic set up will be key as low pressure to the north and high pressure to the south will dictate the system`s path either toward our region our or out to sea. Keep an eye on the forecast over the coming days and read below for more detailed information. .Previous Discussion (149 PM Saturday)... .SHORT TERM... A broad trough will remain over the western U.S. into early next week, and a shortwave digging down the western side of the trough will develop into a weak low off the south-central California coast. This will result in a very subtle cooling west of the mountains and subtle warming for the mountains and deserts Sunday through Monday, but in practice temperatures will still feel very similar to today. However, the low will bring nightly and morning low clouds back to our coastal areas. Low clouds will struggle to form for most of tonight, but an eddy circulation developing early Sunday morning will moisten things up enough to get at least patchy low clouds along the San Diego and likely northern Orange County coastline. Low clouds Sunday and Monday nights will be earlier to develop in the evening and more widespread overnight. Meanwhile, a shortwave trough moving into the Intermountain West will lead to some weakly breezy offshore flow from the east to northeast for the mountains and deserts from the early morning through early to mid-afternoon both Monday and Tuesday. These winds aren`t strong enough for any major impacts, but will lead to drier conditions in these areas than past days. && .LONG TERM... The weak closed low off the south-central coast will merge into the broader trough and move to the northeast late Tuesday into Wednesday as the west end of a broad high over the southern U.S. nudges into the area. This will result in a warming trend Tuesday through the mid to latter half of next week. Meanwhile, a large low pressure system will drop south out of the Gulf of Alaska and make its way down the West Coast. Simultaneously, the developing tropical system Priscilla south of Baja California will gradually make its way northwest through next week, likely leading to some amount of remnant moisture moving into Southern California by late Thursday/Friday. There is significant differences in model output for where the low from the northwest will set up, as well as the track of the tropical system and how much moisture it will advect into the area. There is the possibility for dry weather to continue all weekend (most likely at this moment) as well as for a quite wet weekend in some areas (currently an outside chance). This is leading to a low confidence forecast for temperatures, winds and possible convective rainfall for the latter part of next week. For now, the forecast is for near the zero chances for rainfall increasing to a small chance (10-15%) by late Thursday, followed by slight chances (15-20%) over the mountains and parts of the deserts and less than 15% chances elsewhere Friday and Saturday. Any moisture would be fairly elevated at first, resulting in those higher chances over the mountains, but if we get strong enough forcing from troughing nearby, showers west of the mountains would not be out of the question, as indicated by a handful of ensemble members. Currently chances for thunderstorms are too low to include in the forecast. && .AVIATION... 050300Z....Coasts/Valleys...As of 03z Sat, clear skies prevail. Low clouds with bases 1500-2500 ft MSL to slowly start to develop in very patchy fashion throughout the coastal basin. Eventually, by 10- 12z tonight, confidence increases for greater BKN coverage across SD county and coastal Orange County. Most clouds scatter out to the coast 17-19z with a slight chance for off-and-on SCT-BKN cigs to linger through the afternoon at the immediate SD county coastline, including at KSAN. Clouds with similar bases will start to develop after 00z Mon at the coast, broadening in coverage, and eventually filling into all of SD/Orange County lowlands overnight. Mountains/Deserts...VFR conditions will prevail into Sun night. && .MARINE... No hazardous marine conditions are expected through Wednesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ UPDATE...APR PUBLIC...CSP AVIATION/MARINE...Westerink