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Area forecast discussion 
National Weather Service San Diego California
930 am PDT Monday may 4 2015

a low pressure system off the coast will bring a few showers and
thunderstorms to the mountains and deserts through this afternoon.
Cool weather will occur today with only partial afternoon clearing
near the coast. There will be locally gusty west winds in the
deserts tonight. Slight warming will occur inland Tuesday after the
low pressure system moves east out of the region...but then another
trough of low pressure will build over the West Coast Wednesday
through Friday and bring more cool weather and a chance of
precipitation Thursday and Friday. Fair weather should return over
the weekend.


Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino

Isolated showers were occurring over central and eastern San Diego
County this morning...with one thunderstorm just a bit further east
in Imperial County. A lot of stratocumulus was occurring in coastal
and valley areas...and this will continue most of the day due to a
deep marine inversion...about 3500 feet deep and 4-5 degree c strong.
With the upper low gradually moving east over Southern
California...combined with moisture in the 700-600 mb layer and
MUCAPE in that layer as high as 300-500 j/kg this afternoon...there
should be isolated thunderstorms in the mountains/deserts. 14z hrrr
should explicit precipitation locally over 1/2 inch over the
mountains...though with rather limited moisture...most areas will
receive little or no precipitation as the one-inch precipitable water
values on the GPS met maps are over Imperial County with values
mostly around 0.8 inches over San Diego County/western
Riverside/southwestern San Bernardino counties. With the cool air
mass...maximum temperatures this afternoon will generally be 5-10 degree f below

After the low moves east...fair weather will return for
tonight/Tuesday...though the marine layer will be deep west of the
mountains with local WRF showing a lot of cloud cover...even in some
areas Tuesday afternoon...and again Wednesday afternoon. There could be
drizzle at night...especially Wednesday morning with a short wave moving
through. While slight warming will occur inland Tuesday...temperatures will
overall continue below normal the next several days...including when
the next trough builds over the West Coast Wednesday through Friday.
This could bring more precipitation Thursday/Friday...and with the open
troughing and north-south gradients...gusty winds to the
mountains/deserts. The upper low will be closest on Friday...and
that could bring snow levels down to 5500-6000 feet the
higher mountains could have some light snow. So far...the GFS and
ecm both have low quantitative precipitation forecast values...generally less than one-quarter inch
of precipitation. After the trough moves east...fair weather will return
over the weekend with temperatures recovering to near normal by


041605z...coast/valleys...ovc-bkn stratus 40-50 sm inland...with
bases 2000-3000 feet mean sea level...and tops 3500-4500 feet mean sea level...will partially
clear to the coast through 2000 UTC. The marine layer inversion
strength is about 4 degrees. 2000-05/0000 UTC...unrestricted visible
with with few-scattered clouds 3000-3500 feet mean sea level and few-scattered clouds at or above
10000 feet mean sea level. Locally broken clouds 3000-3500 feet mean sea level possible. 05/0000-
1500 UTC...stratus moving back inland deep into the valleys...with
similar bases and tops to this morning. Forecast confidence moderate-

Mtns/deserts...mountain obscuration of coastal slopes below 4500 feet mean sea level
elevation due to low clouds intersecting terrain will continue this
morning...partially clear this afternoon...then develop again
tonight into Tuesday morning. Scattered-broken clouds between 7000 and 15000
feet mean sea level...with embedded showers over the lower deserts...will
continue this morning...and then develop over the mountains and high
deserts as well...with the possibility of thunderstorms/heavy
showers. Cumulonimbus tops 25000-30000 feet mean sea level. Thunderstorms/showers should
dissipate after 05/0000 UTC...with unrestricted visible and mostly sky clear
expected. After 05/0000 UTC...20-25 knots west winds with gusts to 35
knots over mountain ridges...through and below canyons/passes...along desert
slopes and into adjacent Lower Desert areas...will produce moderate-strong
uddfs/low level wind shear over and east of the mountains


905 hazardous marine weather is expected through Tuesday.
Breezy northwest winds...with gusts of 20 to locally 25 knots...are
possible in the afternoons and evenings Wednesday through
Friday...mainly in the outer waters near San Clemente Island. A
trough moving across the region will create a slight chance of
showers Thursday and Friday.


905 am...nearshore buoy reports show south-southwest swells peaking
this morning...with a significant wave height at 5 feet with a period
of 20 seconds...and surfline surf observations show 6 to 10 foot
surf in Orange County...5 to 7 foot surf along favored beaches in
San Diego County...and 15 to 18 foot surf at The Wedge. These swells
will hold steady through the day today...resulting in continued
hazardous swimming conditions at the local beaches...with surf of 6-
10 feet and 12 foot sets in Orange County and northern San Diego addition to powerful rip and longshore currents...beach
erosion and possible minor tidal flooding of low-lying vulnerable
coastal areas during the evening high tides. The smaller energy
swell should drop-off on Tuesday...but the larger swell will still
be going 4-5 feet/16-17 seconds...and so high surf should
continue that day. It is not until Wednesday that the swell is
expected to drop below 4 feet...with surf falling as well. The swell
will then continue to fall into the end of the work-week. A high
surf advisory is in effect through Tuesday evening. Please see
laxcfwsgx for further details.


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


Sgx watches/warnings/advisories...
California...high surf advisory until 11 PM PDT Tuesday for Orange County
coastal areas-San Diego County coastal areas.





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