316 FXUS66 KSGX 200926 AFDSGXArea Forecast Discussion National Weather Service San Diego CA 226 AM PDT Sat Sep 20 2025
.SYNOPSIS... Warm and dry today. Tropical moisture returns tomorrow morning with periods of light to moderate rain showers by later in the afternoon and into the evening, being mostly widespread across San Diego County and the mountains. Storm chances become confined to the mountains on Monday, followed by the potential for more widespread precipitation Tuesday, depending on the track of the upper low. Drier on Wednesday, and then remaining dry and slightly warmer Thursday and Friday.
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.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...
Today through tomorrow...
At 1:45, satellite imagery is showing a the patchy development of the marine layer, which should continue to gradually fill in and extend inland into portions of the inland valleys. There is still moisture in place from the remnants of Mario, which continue to exit the region as a trough to the west begins to deepen as the subgradient jet max exiting this trough will help to move out any of the remaining moisture with most of the mid to upper levels drying out by later in the day. Because of this, it will likely remain dry across the CWA this afternoon, with perhaps only a few towering cumulus clouds developing over the mountains, with a very slight chance that one materializes into a shower. Otherwise, conditions will be much drier for today, and notably warmer as well, especially for the deserts. By tomorrow, the trough to the west of SoCal will slightly deepen. Meanwhile, there will be some more subtropical moisture streaming up from the south. The trough will help to draw up the moisture, with some showers (mainly light) beginning by later in the day tomorrow. High res models show that the majority of this moisture will be passing over San Diego County, with the highest probability of developing storms over the San Jacinto Mountains and northern mountains in San Diego County by later in the afternoon on Sunday. Rainfall amounts on Sunday will generally be very sparse and minimal (generally less than a tenth of a inch for most areas), unless there are some heavier cells embedded within the band of more stratiform type rainfall. High temperatures on Sunday will also be cooler, and below average for the inland areas and deserts.
Monday through Friday...
On Monday, the low will continue to deepen and eventually begin to cut off. Deterministic models and CAMs alike which go out far enough display more of an abundance of moisture being advected up into the trough going into Tuesday, which will help to increase the chance of showers and thunderstorms. Depending on where the position of the associated U/L low is on Tuesday, will determine how much precip the area receives. By Wednesday, deterministic models do have some agreement that shows the U/L low beginning to slowly propagate to the north slightly and may allow for more of the energy to be displace further north as well, which may allow for a bit of a lull in terms on precipitation if this comes to fruition. The U/L low will continue to meander and remain nearly quasi-stationary going into the later part of next week, which will keep a slight chance of showers/thunderstorms around (mainly over the mountains), as well as temperatures continuing to be on the relatively cooler side throughout the rest of the week. The marine layer will also become more persistent during this period in the forecast as the onshore flow becomes more predominant, and winds will also become more enhanced with the influence of the trough as well for each afternoon towards the end of next week, especially for the areas prone to gap flow winds.
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.AVIATION... 200900Z....Coast/Valleys...Low clouds based 700-1100 ft MSL are slowly forming along the coastline, eventually developing up to 15 miles inland. VIS locally 0-5SM in some inland valleys where terrain and clouds intersect, though reduced VIS and BR is also possible closer to the coast as well. Clouds scatter to beaches 16-18Z. Patchy clouds with lower bases 600-900 ft MSL will form in areas along the San Diego coast after 21/03Z, then gradually spread into coastal sites through about 09Z.
.Mountains/Deserts...VFR conditions and mostly clear skies through early Sunday. Mid and high level clouds AOA 10,000 ft MSL enter the region late Saturday.
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.MARINE...Slight chance for a few thunderstorms over the waters overnight Monday into Tuesday afternoon. Any storm could briefly produce lightning, gusty erratic winds, and choppy seas. Otherwise, no additional hazardous marine conditions are expected through Wednesday.
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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...Stewey AVIATION/MARINE...Westerink
NWS SGX Office Area Forecast Discussion