Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Diego California
915 PM PDT Wednesday Apr 23 2014

Synopsis...
weak high pressure aloft will bring fair weather Thursday. A
strong...cold low pressure system will move across Southern
California Friday and Saturday scattered showers along and west of
the mountains and gusty west winds in the mountains and deserts.
A ridge of high pressure building over the west will bring
much warmer weather next week.

&&

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

A few high clouds were moving over the region this
evening...otherwise skies were clear. No sign of marine
stratus...though a few patches may develop over the coastal waters
late tonight as a coastal eddy spins up. Fair weather Thursday with
high temperatures near to slightly above seasonal averages.

A large and cold upper level trough begins to dig off the West Coast
as it progresses eastward on Friday. This will bring cooling with a
return of coastal low clouds and fog on Friday. Gusty southwest to
west winds will develop over the mountains and deserts Friday
afternoon and evening...peaking Friday night with gusts 40 to 60
miles per hour. A few light showers are possible Friday afternoon...mainly
along the coastal slopes of the mountains.

The trough axis swings through Southern California late Friday into early
Sat. There are still some minor differences in model solutions
regarding the timing and track of the trough. The GFS...NAM...and
UKMET are all slightly faster and less amplified...while the ec and
Gem are a little slower...dig the trough further south...and form a
closed low over Southern California. Either solution will result in rain and
show showers and strong gusty winds in the mountains and deserts.
However...the colder and more unstable ec/Gem solution would bring a
greater threat of thunderstorms and lower snow levels. At this time
have gone with something in between.

The majority of the showers will occur Friday night into Saturday
morning. Coastal and valley locations will likely see less than
one-quarter inch of rain. However...strong upslope flow along the
coastal mountain slopes will generate rainfall totals of around 0.50
to 0.75 inches...with isolated amounts near one inch along the
favored west facing slopes. Snow levels will lower to around
4500-5500 feet by Saturday morning. Ski resorts should see around 1-2
inches of snow...with 2 to 4 inches at the highest peaks of the San
Bernardino and Riverside County mountains. Showers will taper off by
Saturday afternoon...and gusty west winds will subside by Saturday
night.

An upper level ridge of high pressure begins to build along the West
Coast on Sunday and will continue to amplify through Tuesday. This
will bring a warming trend with temperatures in the 80s and 90s in the
lower elevations and upper 60s and 70s in the mountains Tuesday and Wednesday.
Otherwise fair weather with periods of weak offshore flow for the
early to middle part of next week.

&&

Aviation...
240300z...coast/valleys...mostly clear skies with scattered cirrus through
early tonight. Few/scattered low clouds may return to the coast by early
Thursday morning with bases around 1500 feet mean sea level and tops 1800 feet
mean sea level...but should not affect the coastal airports. Confidence is
moderate. Any low clouds that do form will dissipate by middle Thursday
morning...leaving mostly clear skies and unrestricted visible. Low
clouds with bases between 1000-1300 feet mean sea level and tops 1500 feet mean sea level will
form along the coast and push inland after 25/0200z Thursday
evening.

Mtns/deserts...mostly clear with unrestricted visible through Thursday
evening.

&&

Marine...

Friday afternoon through Sat...20-30 knots winds are likely to develop
over the coastal waters...accompanied by a steep west-northwest swell.
Confidence is high this will generate conditions hazardous for small
craft during this period.

A 4 feet long-period south swell this weekend may produce high surf
conditions with sets of 7 to 8 feet along favored south-facing beaches
of Orange County. Strong longshore and rip currents are likely at
many beaches of San Diego and Orange County as well.

&&

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

&&

Sgx watches/warnings/advisories...
California...none.
Pz...none.

&&

$$

Public...sunset
aviation/marine...jt