Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

126 pm PDT Fri Sep 30 2022

Synopsis

The marine layer will be the main weather feature west of the mountains this weekend, with widespread night and morning low clouds and fog, and limited clearing over coastal areas in the afternoons. Patchy drizzle is possible in the mornings as well. It will be cooler through Sunday, with higher humidity. That increased moisture will also set up a chance for isolated thunderstorms over the mountains both Sunday and Monday afternoons. After Monday, a weak ridge aloft will bring drier and slightly warmer days.

Discussion

For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,

Marine layer stratus was still quite extensive offshore this afternoon along the CA Coast and out to sea. While most areas will see afternoon clearing, it may only be temporary for some coastal areas this weekend. Weak onshore gradients will maintain SW-W winds and afternoon sea breezes each day with strongest gusts of 25-30 MPH late each day. Low clouds will begin spreading back inland this afternoon, and move well inland again tonight.

A weak trough will deepen a bit more along the coast through Saturday, helping to deepen the marine layer further into Saturday morning. Given the extensive stratus layer offshore, expect this will continue to be a prominent feature in the weather this weekend west of the mountains. The cloud layer will be thick enough for some patchy drizzle as well. The clouds and onshore flow will also keep daytime temperatures a bit below average west of the mountains, while average of above temps prevail over the mts/deserts.

Drier air has moved across SoCal from the NW, as we feel the fringes of a deep upper low developing over the northern Rockies. The drier air should stick with us through Saturday, but is forecast to be replaced by Sunday as SE winds develop aloft and draw a very moist subtropical airmass back over us. As it moves in, humidity will rise, and mid-level clouds will develop, possibly feeding into isolated thunderstorm activity over the mountains by Sunday afternoon. The elevated moisture levels will stick with us through Monday, so a slight chance of showers and thunderstorms will persist. The threat for showers will decrease as the low and associated trough over the Rockies and Great Basin moves eastward. Developing northerly flow aloft will follow by mid next week, and will bring in drier and more stable conditions, while a ridge along the coast suppresses the marine layer. All of this will contribute to warmer days and fry weather with less marine clouds for the latter half of next week.

Aviation

302030z, Coast/Valleys, Patches of low clouds at the immediate coast. Bases are 1500-2000 ft MSL with tops to 2300 ft MSL. Low clouds begin to spread inland again after 00Z Sat reaching up to 30 miles inland by 14Z Saturday. High confidence for CIG impacts at coastal TAF sites 03Z-18Z Sat. Moderate confidence for CIG and VIS impacts at KONT and KSBD 10Z-16Z Sat

Mountains/Deserts, Mostly clear with unrestricted VIS through tonight.

Marine

No hazardous marine weather is expected through Tuesday.

Watches, Warnings, Advisories

Ca, None. PZ, None.

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