763 FXUS66 KSGX 021640 AFDSGXArea Forecast Discussion National Weather Service San Diego CA 940 AM PDT Thu Oct 2 2025
.SYNOPSIS... Cooler conditions with an uptick in winds in the mountains and deserts Friday. In addition, the marine layer will deepen with low clouds expected to spread into portions of the inland valleys for tonight and Friday night. Slightly warmer Saturday west of the mountains in weak offshore flow. Cooler conditions expected Sunday and Monday with warming next Tuesday and Wednesday.
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.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...
Today is expected to be 3 to 7 degrees warmer than yesterday for inland locations, with no change or a degree or two of cooling along the coast. A trough of low pressure is expected to move into California on Friday and east into Nevada on Saturday. This will bring 3 to 5 degrees of cooling to inland areas on Friday, with an increase in winds for the mountains and deserts. Wind gusts are expected to peak at 35 to 45 mph Friday afternoon and evening. Additionally, with the increase in onshore flow the marine layer is expected to deepen. Areas of low clouds are expected to reach into the valleys for tonight into Friday morning.
As the upper level low moves over Nevada Saturday, the overall flow will quickly switch to offshore by early Saturday morning. The north/northeasterly winds associated with the offshore flow are expected to be fairly weak and localized to the San Bernardino and Santa Ana coastal mountain slopes. While the marine layer will still be fairly deep, any low clouds that develop Friday night into Saturday are expected to clear fairly quickly in the Inland Empire and Orange County. Highs on Saturday are expected to be a few degrees warmer than Friday west of the mountains, likely due to the weak offshore flow. Temperatures in the deserts will continue to cool a few degrees into Saturday.
A broad trough of low pressure will set up over the western United States on Sunday. This will result in a few degrees of cooling west of the mountains, with additional cooling expected into Monday for most locations. For next Tuesday and Wednesday, the pattern becomes a little more uncertain with ensemble guidance struggling to pin down the amplitude and position of the aforementioned trough. The solution with a weaker and deeper trough over California would continue the cooler conditions while the solution with the trough to our east with weak ridging over California would bring slightly warmer conditions. Current forecast follows the NBM which leans towards the warmer solutions for next Tuesday and Wednesday.
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.AVIATION... 021615Z....Coasts/Valleys...Variable low clouds based 1000-1500 feet MSL will scatter out completely within the next hour or so. Low clouds will redevelop after 03Z for the coastal areas initially, and after 08Z inland tonight into Friday. Bases should be around 1500 feet MSL, rising over 2000 feet MSL early Friday, filling much of the coastal basin. They will begin to scatter out beginning around 16-17Z for the inland areas, and then eroding away from east to west to the coastal areas by around 18-19Z Saturday.
Mountains/Deserts...Mostly clear and VFR conditions today and tonight.
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.MARINE... Northwest winds Friday afternoon and evening over the outer waters near San Clemente Island could lead to hazardous conditions for small craft. Otherwise, no hazardous marine conditions are expected through Monday.
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.SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.
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.SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None.
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PUBLIC...CO AVIATION/MARINE...Stewey
NWS SGX Office Area Forecast Discussion