Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 201113 CCA

Area Forecast Discussion
National Weather Service San Diego CA
412 AM PDT Sun May 20 2018

corrected to add beaches section

A trough along the West Coast and a coastal eddy will continue
cool weather today with extensive night and morning low clouds
along and west of the mountains. Sunny skies will continue over
the mountains and deserts with gusty west winds at times. On
Monday and Tuesday a deeper low pressure system will bring
additional cooling and a chance for afternoon showers and
thunderstorms over the mountains and high deserts. It will be dry
and a little warmer Wednesday through Friday.



Extensive low clouds again this morning given a deep marine layer
and onshore flow. Clouds will be slow to clear again today with
partly to mostly cloudy conditions likely near the coast most of
the day. Temperatures will again be on the cool side except near
the coast which will actually be near normal.

On Monday an anomalously cold upper low pressure area will drop
into the Mojave Desert and linger through Tuesday slowly moving
NE. This will help to increase the onshore flow and bring gusty
winds to the mountains and deserts with some blowing dust/sand
possible in the lower deserts. At this time winds are likely to be
marginal for a wind advisory with occasional gusts of 45 mph
mainly in the Riverside and San Diego County Mountains and

Proximity to the upper low will bring enough forcing and
instability with a narrow ribbon of mid level moisture to generate
scattered showers and perhaps a few thunderstorms over the
Riverside and San Bernardino County Mountains and the Mojave
Desert portion of San Bernardino County. With modest moisture
parameters any thunderstorms that do form could be capable of
gusty downdraft winds and dry lightning. Pops were increased a bit
with this forecast mainly over the San Bernardino Mountains on

Weak ridging is likely to develop Wednesday through Friday with
some warmer weather for inland locations, meanwhile the marine
layer should retreat a bit with low clouds staying a little closer
to the coast than the last several days.

The latest medium range models are trending with a little better
consensus regarding the potential for another anomalous upper
low. The latest trends look to shift the track of the upper low
further north again more over Norcal with a drier flow over SoCal.
Even with this pattern we should expect a deeper marine layer at
the coast and a more favorable pattern for the potential for
strong winds.


200905Z...Coast/Valleys...Widespread OVC low clouds cover the areas
west of the mountains again this morning. Bases are 1500-2500 ft MSL
with tops to 3000 ft MSL. Higher terrain will be obscured at times,
with areas of vis 1-3 miles and locally 1 mile or less where clouds
and terrain intersect. Slow clearing will begin inland after 16Z,
with only partial clearing within 15 miles of the coast. Low clouds
increasing in coverage again this evening with similar bases and

Mountains/Deserts...Mostly clear skies with unrestricted vis through
this evening.


No hazardous marine conditions are expected through Thursday.


A long period south-southwest swell from 200 degrees will begin to
build late on Monday, peaking Tuesday afternoon into Wednesday at 3-
4 ft/17-19 sec. The swell will very slowly lower late Thursday and
Friday. This will likely result in a period of high surf along
southwest facing beaches Tuesday into Thursday. Strong rip and
longshore currents and minor beach erosion are also possible during
this period.


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




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