Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 270434

Area Forecast Discussion
National Weather Service San Diego CA
930 PM PDT Tue May 26 2020

Strong high pressure aloft will continue through Thursday,
keeping temperatures well above average in the deserts and
other inland areas. A cooling trend will start Friday west of the
mountains, with high temperatures dropping back down to near
seasonal normals, but the deserts will only have slight cooling
Friday. The marine layer and weak onshore flow will keep coastal
areas cooler with night and morning low clouds and locally dense
fog. Over the weekend and into next week, the marine layer will
deepen and onshore flow will strengthen, spreading low clouds
farther inland, and all areas will continue to be cooler.



Skies were clear except for a few patches of stratus near the coast.
The stratus should become more extensive overnight, and some fog
will develop, with dense fog fairly likely over the coastal mesas
and other elevated terrain near the coast. Aircraft soundings showed
an inversion base around 800 feet MSL, which would support this, and
observations to the west and northwest, such as San Clemente Island,
suggest an even lower inversion (KNUC on San Clemente Island and LAX
have cloud base around 400-500 feet MSL). Most areas should clear by
mid-morning, much like with this morning, but could take until late
morning at the beaches since the local WRF projects the inversion
strength to be around 9 deg C, but without an eddy, then at this
inversion strength, most clouds should be gone by afternoon.

The big story will be the heat inland, and in the forecast update
(including analyzing the highs from today), we increased
temperatures 1-3 deg F inland. 850 MB temps increase by about 1 deg
C from today`s readings in all the main models, so Wednesday should
be the hottest day of the week in most locations. I would not be
surprised to see an isolated 113 deg F reading Wed afternoon.
Thursday should be almost as hot (possibly no change in the desert)
as any 850 MB temp decreases will be minimal and mostly near the
coast. I probably don`t have to say this by now, but remember to
stay safe if you (or a loved one) are out in the heat!

From previous discussion...

High pressure will sit over Southern California through Friday.
Temperatures in the deserts will reach their peak Wednesday and
Thursday with highs in the High Desert reaching 100-103, and
108-112 in the low desert. As the high pressure system begins to
move east on Friday temperatures will begin to slowly decrease.
Temperatures in the deserts will fall to seasonal normals by

West of the mountains, the marine layer will keep temperatures near
the coast in the 70s, with temperatures in the mid-80s to mid-90s
inland. The Inland Empire will see the warmest conditions, with
temperatures locally reaching 15 degrees above normal. Highs in the
IE are expected to reach the upper 90s. These warm conditions are
expected through Thursday, before a cooling trend begins Friday
through the weekend.

An upper level low pressure system will move into northern and
central California late Friday, which will strengthen onshore flow
and deepen the marine layer across Southern California. While there
are still some differences in the details, global ensembles keep a
weak trough along the California coast through early next week. This
will keep temperatures around seasonal normals and spread low clouds
and fog into the western valleys.


270345Z...Coast...SCT005-010 at the coast becoming BKN-OVC004-008
through 09Z and spreading inland with CIGS at KSAN/KCRQ/KSNA between
09Z-17Z Wednesday and visibilities 1-3SM in fog. Dense fog with vis
less than a 1/2 mile most likely at KCRQ. Skies becoming clear after

Valleys/Mountains/Deserts...Mostly clear through Wednesday night.
Haze may limit vis to 4-6 miles at KONT and KSBD from 14-19Z.


Areas of dense fog will impact the coastal waters through Thursday.
Wind gusts to 20 knots are forecast over the offshore waters
Saturday and Sunday. Otherwise, no hazardous marine weather is
expected through the weekend.


There will be a high rip current risk through the weekend as a
series of southwest swells rolls into SoCal beaches. These swells
will generate surf of 3 to 5 feet with occasionally higher sets of 6
to 7 feet in Orange and northern San Diego County beaches.
Conditions will be borderline for a High Surf Advisory (surf of 7
feet or greater) Friday and Saturday.


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


CA...Excessive Heat Warning until 7 PM PDT Friday for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Gorgonio Pass Near Banning.



PUBLIC...Maxwell (Update)/CO (Previous Discussion)
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