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Spring Valley Lake, California Weather Forecast Discussion

678
FXUS66 KSGX 200432
AFDSGX

Area Forecast Discussion National Weather Service San Diego CA 932 PM PDT Fri Sep 19 2025

.SYNOPSIS... Warm and dry Saturday. Tropical moisture returns Sunday morning with periods of light to moderate rain showers into Sunday evening, most 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 or Wednesday depending on the track of the upper low. 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...

Evening update... A couple small showers developed over the Mojave Desert this afternoon. No precipitation expected overnight into Saturday as drier air moves into the region. Otherwise low clouds will develop over the coastal areas and western valleys tonight, clearing by mid-morning Saturday. Only thing of note is that when then cut- off low moves back towards the area sometime in the Tue-Wed time frame, there is the potential for another round of more widespread precipitation, though there is currently little ensemble consensus on the timing and track of this low.

Previous discussion... Given lower dew points and less cloud cover tonight and tomorrow, more seasonable temperatures ensue, with highs in the 70s and 80s for coasts/valleys, 60s and 70s for the mountains, and upper 90s for the deserts. On Sunday, tropical moisture once again pushes up into Southern California from a developing system off of Baja. Hi-res models are pulling the moisture up as early as Sunday morning, spreading over San Diego County and then up into Riverside, Orange, and San Bernardino counties by the afternoon. Soundings show significantly drier air in the lower levels with most of the moisture elevated, indicating better rainfall chances will be in the mountains, but isolated spots of 0.50" rainfall totals throughout the day Sunday are not out of the question. This pattern is especially difficult to resolve and confidence in how far north the moisture makes it as well as the drier air at the lower levels will make or break this event. Regardless, better moisture and ample cloud cover should make for slightly cooler temperatures on Sunday compared to Saturday.

Additional moisture will surge into the region Monday-Wednesday, with less confidence in the overall upper level pattern. Rain showers will be possible during this time, with thunderstorm chances returning primarily for the mountains by Monday afternoon and becoming more widespread on Tuesday. At this point the spread in models is a bit too great to nail out the details, but confidence in precipitation/storm chances will be highest in the mountains for the Mon-Wed time frame. With the incoming clouds and moisture, temperatures will hold fairly steady into the end of next week.

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.AVIATION... 200345Z....Coast/Valleys...Low clouds based 900-1300 ft MSL are forming along the San Diego coastline. These will gradually make their way north, likely impacting the Orange County coast by 12Z (70% chance for CIGs by this point, including at KSNA), as well as inland up 10-15 miles. CIGs will lower slightly overnight, likely to below 1000 ft MSL for the majority of sites, along with vis lowering to 3-6 SM over coastal highlands. 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 Saturday.

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.MARINE...No hazardous marine conditions are expected through Wednesday morning.

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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...SS/Zuber AVIATION/MARINE...CSP

NWS SGX Office Area Forecast Discussion

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