Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 201626

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

Quiet weather will prevail today, with slow to limited clearing
along the coast. An area of low pressure should bring isolated
thunderstorms to the Mojave Desert and San Bernardino County
Mountains Monday afternoon, with other areas remaining dry.
Weak ridging is expected to usher in a limited warming trend to
end the workweek. At the beaches and early season south swell
will bring elevated surf for most of the workweek.



At 9 AM...An weak upper level trough was in place along the West
Coast. A few light showers were occurring in the Pacific
Northwest, otherwise dry conditions prevailed. In SoCal the
marine layer was around 3000 ft deep, with extensive low clouds
over from the coastal waters to the coastal slopes. A few wispy
cirrus were also drifting over the region. At the surface winds
were light, with a few patches of very light drizzle reported near
the coast this morning.

Quiet weather will prevail across the region today, with clearing
of the marine layer being the main forecast challenge today.
Given this mornings high res guidance and the similarity of the
12Z NKX sounding to yesterdays, any clearing at the coast looks
like it will be limited today. The valleys should fair better with
some sunshine by the afternoon. In the mountains and Mojave
Desert there should be enough surface heating for a few cumulus
buildups this afternoon, but showers/thunderstorms are not

A mid level jet (700-400 mb) diving south just off the West Coast
should help the aforementioned weak trough transform into a
closed low over the Mojave Desert by Monday afternoon. This will
bring cooling aloft and steeper mid-level lapse rates. A broad
average of the models suggests that MU CAPE of 200-600 J/kg may
be available during peak heating in San Bernardino County. As
such a showers/thunderstorms appear possible over the San
Bernardino County Mountains and Mojave Desert Monday afternoon.
The one limiting factor may be high cloud cover, which could limit
our ability to reach convective temperatures. Instability should
decreases rapidly as you progress to the south, with little to no
potential for showers/thunderstorms south of the San Bernardino
Mountains. Instability decreases on Tuesday, but an isolated
shower can`t be ruled out in the mountains/Mojave Desert. Coastal
and valley areas will remain dry, with a deep marine layer both
Monday and Tuesday.

Weak ridging should return for the second half of the week,
bringing a slow return to near average temperatures by Friday.
Night and morning low clouds will continue over coast and valleys,
with variable levels of stickiness each day. The most notable
weather feature will likely be elevated surf at the beaches from
an early season south swell.


201615Z...Coast/Valleys...Widespread OVC clouds with bases 1700-2500
ft MSL and tops to 3300 ft MSL will very slowly clear in the valleys
through 21Z, with little or no clearing within 10-15 miles of the
coast this afternoon. Most vis will be above 5 miles below the
clouds. OVC stratus will be widespread again tonight with bases 1500-
2000 ft MSL and tops to 3500 ft MSL. Higher terrain will be obscured
at times.

Mountains/Deserts...Mostly clear skies with unrestricted vis
will continue through tonight. Areas of west surface winds 15-25
knots with gusts 25-35 knots will occur late this afternoon/evening
over the desert mountain slopes and through San Gorgonio Pass.


No hazardous marine conditions are expected through Thursday.


A long period south-southwest swell from 200 degrees will begin to
build late Monday, peaking late Tuesday through Wednesday at 3-4
ft/17-19 sec. The swell will very slowly lower Thursday through
Friday. This will likely result in a period of high surf along
southwest facing beaches Tuesday through Thursday, with some sets 6-
8 feet in Orange County. Strong rip and longshore currents and minor
beach erosion are also possible during this period.


Skywarn activation will not be needed today. Activation is
unlikely on Monday, but spotters (especially in San Bernardino
County) are encouraged to report significant weather.




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