Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 211054

Area Forecast Discussion
National Weather Service San Diego CA
354 AM PDT Mon May 21 2018

Low pressure will develop southward across California tonight and
Monday, maintaining a deep marine layer, clouds, and areas of
drizzle nights and mornings west of the mountains. Cooling aloft may
even spark a few isolated thunderstorms over the Mojave Desert and
San Bernardino Mountains Monday afternoon. The low moves east by
midweek, resulting in a modest warming trend into the weekend. At
the beaches...a south swell will bring elevated surf much of the



The deep marine layer continues this morning and healthy onshore
gradients around 8 mb as the upper low pressure approaches from
the NNW. Cloudy conditions will give to partial clearing this
afternoon inland valleys with some high cloudiness at times.
Low clouds will linger through the afternoon near the coast and
the western valleys.

The compact upper low was passing near SF into the San Joaquin
Valley early this morning and will continue to drop SSE and settle
over the Mojave Desert this afternoon. This will help to
destabilize the atmosphere and bring some lift to generate
scattered showers and a few thunderstorms over the Mojave Desert
and the San Bernardino Mountains, mainly along the north facing
slopes. The best chance of showers/t-storms will be mid afternoon
through early evening. Any storms that form could contain gusty
downdraft winds and small hail.

Gradient driven winds will be favored with the best chance of
strong winds over the San Diego County Mountains and the lower
deserts. Winds will be marginal for wind advisory but a few gusts
around 50 mph will be possible later today and this evening. Areas
of blowing sand and dust will be possible in the lower deserts and
have been expanded in the forecast to better highlight the

The upper low will gradually move NE and into NV and UT on Tuesday
reducing the chance of any precipitation over SoCal.

Weak upper level ridging brings a warmup for inland areas
Wednesday through Friday with the marine layer keeping things on
the cool side near the coast. Temperatures will warm to near
normal levels inland however.

Things get kinda interesting again by next weekend with a lot of
forecast uncertainty with another closed upper low dropping SE
towards California Friday night or Saturday. There is still a lot
of uncertainty with the EC being more consistent run to run with a
further north track over NorCal with limited impacts to SoCal
except for the potential for strong onshore winds. The GFS is much
further south with the track of the upper low which could bring
some more direct impacts with a chance of showers again and much
cooler weather. For now we continue to favor the EC forecast which
has been more consistent lately with the track forecast and no
significant changes have been made to the extended forecast at
this time.


210900Z...Coast/Valleys...Low clouds with bases 1800-2500 feet MSL
with tops to 4500 feet filling the coastal basin this morning.
Occasional bases down to 1000 feet msl along with 3-5sm vis in -DZ,
especially near the coast. Only partial clearing expected inland and
little to no scatter out near the coast. Higher terrain will be
obscured at times between 2000-4000 feet. Low clouds will fill the
coastal basin again tonight with similar bases and tops.

Mountains/Deserts...A batch of high clouds this morning will give
way to mostly clear skies with unrestricted vis today and tonight.


No hazardous marine conditions are expected through Friday.


A long period swell from 200 degrees will begin to arrive late
today, and peak late Tuesday through Wednesday before subsiding
slowly Thursday and Friday. Surf of 4-6 feet with some sets to 7
feet is expected on south facing beaches late Tuesday through
Thursday, along with strong rip and longshore currents.


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




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