643 FXUS66 KSGX 081014 AFDSGXArea Forecast Discussion National Weather Service San Diego CA 314 AM PDT Wed Oct 8 2025
.SYNOPSIS... A low pressure system off the West Coast will draw tropical moisture northward into the area for Thursday into Friday night with increasing chances for showers and a chance for thunderstorms. Cooler with drying for Saturday through Monday. For Tuesday and Wednesday of next week, a low pressure system moving to near the West Coast will bring a chance of showers.
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.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...
.SHORT TERM (Today through Friday)... The marine inversion has slowly strengthened and decreased slightly in depth over the past 48 hours with coastal low clouds not spreading as far inland into the San Diego County valleys as the past two mornings. Not much change in high temperatures is expected for today with high temperatures a few degrees below average for the coast into portions of the valleys and a few degrees above average for the mountains and high desert. High temperatures for today will range from around 70 near the coast to the 80s for the Inland Empire with the mid to upper 90s for the lower deserts.
For Thursday into Friday night, a large low pressure system centered off the West Coast will draw moisture from the remnants of weakening Hurricane Priscilla northward into the area, increasing chances for showers and thunderstorms. The greater chances for heavier rainfall are from the mountains of San Bernardino, Riverside, and San Diego Counties eastward across the deserts into Arizona with decreasing chances toward the west.
Higher-resolution model guidance shows bands of showers with a slight chance of thunderstorms moving northwestward across the area on Thursday morning with additional chances for showers and thunderstorms during the afternoon more focused over the mountains eastward across the deserts. Chances for showers and thunderstorms will continue at times through Friday into Friday evening. NBM chances for one inch or more of rainfall is around 5 percent for the mountains. However, the HRRR does show the potential for 6-hourly rainfall to around 1.5 inch for portions of the mountains and deserts for Thursday afternoon.
High temperatures for the mountains and deserts will be a few degrees cooler for Thursday and again for Friday. With the influx of tropical moisture and increase in clouds, Thursday night will be warmer with low temperatures for early Friday as much as 15 to 20 degrees above average for the mountains and deserts of San Diego County.
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.LONG TERM (Saturday through Tuesday)... There will be drying and cooler days for the weekend through Monday with high temperatures on Monday as much as 12 to 18 degrees below average for the higher elevations of the mountains. High temperatures on Monday will range from around 70 near the coast to the 70s for the Inland Empire with the mid 80s for the lower deserts.
For Tuesday and Wednesday, another low pressure system nearing the West Coast may spread showers southward into southwestern California. Cluster analysis shows the clusters with the relatively wetter solutions are those with the low pressure system slightly stronger and centered slightly farther to the west. NBM chances for measurable rainfall for Tuesday morning through Wednesday night is generally 20 to 30 percent for the coast to the mountains with chances for one inch or more of rainfall as much as 5 to 10 percent for portions of the mountains.
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.AVIATION... 080930Z....Coasts/Valleys...Low clouds will continue to gather across all coastal areas and some of the valleys through 14Z. Bases will be 1000-1500 feet MSL with tops to 1900 feet. Vis reduced 0-5SM inland. Scatter out 16-19Z. Areas of low clouds with bases around 1500 feet MSL will gradually develop after 03Z into Thursday, but with less uniform coverage and less inland extent.
Mountains/Deserts...Mostly clear and VFR conditions today and tonight.
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.MARINE... Wind gusts around 20 kt near San Clemente Island Thursday and Friday afternoons and evenings. There is a slight chance of thunderstorms Thursday through Friday. Lightning, erratic winds, choppy seas, and/or reduced visibility in heavy rain likely in vicinity of any thunderstorms.
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.BEACHES... There is a 5-15% chance of thunderstorms producing lightning Thursday through Friday.
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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...17 AVIATION/MARINE/BEACHES...MM
NWS SGX Office Area Forecast Discussion