Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

200 pm PDT Wed aug 12 2020


High pressure aloft will prevail over the southwestern US and bring very hot weather to most inland areas, especially Friday through Monday. Elida, which has weakened to a tropical storm and is approximately 700 miles south of San Diego, will increase the moisture aloft and bring some clouds and a small amount of precipitation to parts of the area. An isolated thunderstorm is possible in the mountains Thursday, with increasing chances of mountain and desert thunderstorms Friday through early next week. Only patchy night and morning low clouds and fog is expected near the coast the next several nights.


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

Partly cloudy skies prevailed early this afternoon with the mid and high clouds evident due to the moisture increasing aloft. It was hot in the deserts, with 109 at PSP as of 1 PM.

Weakening Tropical Storm Elida was about 700 miles south of San Diego, moving northwest and sending some moisture over our area. With the strong high pressure aloft over the southwest, southeast flow will prevail here, with models showing a lot of moisture from the southeast in the 700-500 MB layer, enough that at least isolated thunderstorms could occur almost any day over the mountains and some adjacant deserts. The best chances should be around Sun/Mon next week when instability increases, and moisture is greatest. Nbm 1-D viewer even has 20+ chances of thunderstorms then over much of the mountains and deserts.

The heat will be the big story with 850 MB temps over 30 deg C at times. Ecmwf ensemble maxT values could be as high as around 120 deg F in the lower deserts, but most areas will be closer to 115 there. 100 deg F temps or higher could occur in inland OC, with 100-110 in the Inland Empire, all Fri-Mon, which highest temps generally Fri- Sun. Near the coast, it will be cooler, partly due to ocean water temps in the 60s, and an eddy could develop around Sunday, though to bring cooling a little bit inland, though that is low-confidence. Longer range ECMWF/GFS ensembles should little respite from the desert heat even after Monday, and even the cooling trend in the valleys should be modest, according to most of the ensemble solutions.

Near the coast, any low clouds and fog that occur will be patchy, but due to the shallow marine layer, some dense fog could occur at times, including late tonight.


122000z, Coast/Valleys, High clouds AOA 10,000 feet MSL will persist across the region through tomorrow. Low clouds will be less widespread tonight into Thursday morning, with coverage mostly confined to the coast. Low confidence in impacts to coastal terminals. Vis restrictions of 1-3 SM, locally lower, possible where low clouds do form.

Mountains/Deserts, SCT high clouds AOA 10,000 feet MSL will persist across the area through tomorrow. No vis restrictions expected.


Patchy fog with visibility 1 nautical mile or less could develop over the coastal waters each night and morning through this weekend. Otherwise, no hazardous marine weather is expected through Monday.


The south-southwest swell will continue to diminish into the afternoon. Surf of 2-4 feet with moderate rip current risk is expected through the weekend.

Watches, Warnings, Advisories

Ca, Excessive Heat Warning from noon Friday to 9 PM PDT Monday for Apple and Lucerne Valleys-Coachella Valley-Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Deserts-San Diego County Mountains-San Diego County Valleys-San Gorgonio Pass Near Banning-Santa Ana Mountains and Foothills.


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