Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

900 pm PDT Tue Sep 27 2022

Synopsis

Hot conditions will continue across the region through tomorrow. Increasing moisture will lead to a slight chance for showers and thunderstorms on Wednesday across the mountains, High Desert and eastern portions of the inland valleys. Greater cooling is expected for Thursday through the weekend.

Discussion

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

Evening Forecast Update:

No updates were needed this evening. Low clouds will begin to form towards midnight near the coast and spread inland a few miles through Wednesday morning.

Previous Discussion (issued at 155 PM PDT):

For Wednesday, increasing moisture will lead to a slight decrease in temperatures by a degree or two region-wide, though highs will remain well above seasonal averages. This will continue to lead to moderate to locally high heat risk across the region. Scattered showers and thunderstorms will be possible through the afternoon, mainly across the mountains, High Desert and eastern portions of the inland valleys. The main threat will be frequent lightning and gusty winds, though heavy rainfall leading to local flooding will be possible.

The ridge will weaken on Thursday as an upper-low moves through the Pacific Northwest. Onshore winds and drying conditions are anticipated for Thursday through the weekend, allowing for cooler temperatures. By Saturday, high temperatures are expected to be near or slightly below average west of the mountains, and slightly above in the deserts.

The 12z ECMWF Ens Mean shows ridging moving into the western United States for the second half of the weekend, with positive height anomalies returning to Southern California Sunday night into Monday. This may lead to slight warming early next week.

Aviation

280400z, Clear for areas 15+ miles inland tonight. Moderate confidence in cigs forming near the coast 10Z-17Z Wednesday, highest chance at KSAN/KCRQ. BKN-OVC cigs 004-007 ft MSL and vis 1-4SM in BR expected, locally lower vis near higher terrain. TCU with tops near 30-40K ft MSL expected across the mountains after 19Z Wed with ISO TSRA. Gusty and erratic winds with heavy downpours possible near storms until 02Z Thursday.

Marine

No hazardous marine weather is expected through Saturday.

Watches, Warnings, Advisories

Ca, Heat Advisory until 8 PM PDT Wednesday for Orange County Coastal Areas-San Diego County Coastal Areas-San Diego County Valleys-Santa Ana Mountains and Foothills.

Excessive Heat Warning until 8 PM PDT Wednesday for Coachella Valley-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Deserts-San Gorgonio Pass Near Banning.

PZ, None.

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