Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 122106 CCA

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.



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

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.

Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


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




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