Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 282009

Area Forecast Discussion
109 PM PDT Sun May 28 2017

Weak high pressure aloft will bring warmer weather inland through
Tuesday, while the marine layer keeps the coast seasonal with areas
of night and morning low clouds and patchy fog. Cooler, with a
deeper marine layer and more extensive marine clouds midweek as a
low pressure trough develops over the West Coast. Modest warming
returns by next weekend under weak ridging aloft.



Patchy low clouds were observed over the coastal waters at midday,
but had cleared the beaches, otherwise the sky was clear across
SoCal. Marine clouds were extensive west of the islands.
Temperatures were running higher than yesterday inland, especially
at some of the higher elevations. At Noon PST...Julian and Descanso
RAWS sites were 18 degrees F higher than yesterday, Anza was up 15
degrees as well. Surface pressure gradients were flat KSAN to SW NV,
and about 6 MBS onshore to the lower deserts. Peak wind gusts were
below 25 MPH at Noon PST.

Very little change is forecast to the synoptic pattern through Mon,
except for perhaps a weaker offshore sfc gradient from the NE. This
could result in better coastal marine stratus coverage Mon/Tue
mornings, especially given that it is climatologically favored, but
no guarantees.

High latitude ridging over the West will maintain a split flow in
the atmosphere through midweek. The weaker southern branch will
support weak ridging over SoCal and warmer weather through Memorial
Day, then transition again to cooler conditions as a weak upper
trough develops and amplifies the marine layer. The global models
show the pattern repeating again next weekend into the following
week. Weak ridging aloft will lead to warming into the weekend,
followed by low pressure aloft and cooler conditions early next week.

Aside from the fluctuations in daytime temperatures, the pattern
looks seasonal, with onshore flow, locally gusty winds over the
mts/deserts at times, and nocturnal marine clouds varying in extent
and coverage over the coastal basin.


282000Z...Coast/Valleys...Patchy low clouds with bases near 1500 ft
msl will continue over the coastal waters, otherwise SKC and
unrestricted visibility through 03Z Monday. Low clouds with bases
near 1,000 ft msl should filter back along the coast after 03Z.
Ceilings are expected at KSAN, KCRQ and KSNA between 05Z and 17Z
Monday. Low clouds will dissipate after 17Z Monday, resulting in
predominantly SKC and light winds through 00Z Tuesday.

Mountains/Deserts...SKC-FEW AOA 20,000 ft msl, unrestricted
visibility, and light winds through 00Z Tuesday.


Quiet conditions are anticipated through Friday with a mixed swell
(2-4 ft at 6-9 sec from the northwest and 2 ft at 12-15 sec from the
south). Winds will remain light out of the northwest this week, with
the typical afternoon/evening peak in wind speeds. Strongest winds
will be found in the vicinity of San Clemente Island.


Skywarn activation is not requested.





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