Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 292033

Area Forecast Discussion
133 PM PDT Mon May 29 2017

A low pressure trough along the West Coast will bring slow deepening
of the marine layer into Wednesday, with nocturnal marine clouds
and patchy fog spreading a little farther into the valleys each day.
Cooler into midweek with patchy drizzle possible and only partial
clearing in some areas as the marine layer deepens. Warmer again
into the weekend under a weak high pressure ridge aloft, then cooler
early next week as a trough redevelops.



Marine clouds were slowly clearing back to the coast at midday, even
as the higher clouds spread east off the Pacific. The combination of
clouds had resulted in partial sun in many areas west of the mts
this morning, which held temps some 3 to 9 degrees F below values
observed yesterday at 11 AM PDT. Quite hot in the deserts though,
with 105 in Palm Springs and 90s across the high deserts at 1 PM
PDT. Surface pressure gradients were trending a bit better onshore
today at 8 MBS KSAN to the lower deserts at 1 PM PDT. Still, peak
wind gusts were only in the 20-25 MPH range through wind prone
mtn/desert areas.

A low pressure trough in the upper atmosphere along the West Coast
will deepen slightly and drift slowly east through Thursday. This
will deepen the marine layer, and produce more extensive and
persistent marine stratus throughout the coastal basin. Some patchy
drizzle is possible late nights/mornings due to the depth of the
stratus layer. The trough will lift out by Fri, allowing a weak
ridge to build into Saturday. Some reduction in marine layer depth
and stratus coverage is likely inland through the weekend under the

Another, weaker trough arrives Sunday and persists into next week,
maintaining onshore flow and a marine layer with attendant nocturnal
clouds/patchy fog west of the mts. Based on the 12Z ECMWF model run,
the extent and persistence of morning stratus would be more limited
than this week for better clearing.

For temperature trends...Look for slight cooling on Tue, although if
the stratus persists over portions of the Coast/valleys, it could be
more significant. Greater cooling is likely all areas for Wed/Thu as
the marine layer and onshore flow peak. A coastal eddy may develop
at this time as well, limiting clearing. This will drop temperatures
back to levels that are a bit below average for early June.

Warmer by the middle of next week as heights/thickness build,
although there are differences in the global model solutions. The
ECMWF is more aggressive with the ridging along the West Coast than
both the 12Z GFS/GEM.


292030Z...Coast/Valleys...SCT-BKN low clouds with bases near 1,200
ft msl will continue over coastal areas through 02Z Tuesday. Low
clouds should begin to increase in coverage along the coast after
02Z, spreading inland 25-40 miles through 14Z Tuesday. Bases
overnight will be near 1,000 ft msl with tops near 2,000 ft msl.
Visibility restriction of 2 SM or less are likely near the higher
valley terrain. Slow or perhaps only partial clearing is anticipated
Tuesday along the coast, with KSAN, KCRQ and KSNA not clearing until
after 20Z.

Mountains/Deserts...Light winds, unrestricted visibility and SCT AOA
20,000 ft msl will prevail through 00Z Wednesday.


Quiet conditions are anticipated through Friday with a mixed swell
(2-4 ft at 7-10 sec from the northwest and 2 ft at 12-15 sec from
the south). Winds will remain light this week, with a mix of
southwesterly winds in the mornings/early afternoons followed by
more west northwest winds in the late afternoons/evenings.

Skywarn activation will not be needed today.





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