Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Diego California
915 PM PDT Thursday Apr 24 2014

Synopsis...
marine layer clouds and fog redeveloping and spreading inland by
early Friday morning. A strong low pressure trough will move through
late Friday into Saturday...bringing scattered showers...much cooler
weather...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. Periods of offshore winds are possible during
the middle of next week.

&&

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

Low clouds are rapidly developing along the coast this evening. A
coastal eddy spinning up will help deepen the marine layer with low
clouds and fog spreading into the inland valleys by Friday morning.

An upper level trough of low pressure deepening off the West Coast
will move through Southern California late Friday and Saturday. This will
bring considerable cooling Friday and Saturday wit temperatures several
degrees below seasonal averages. Gusty west winds will develop in
the mountains...deserts...and coastal waters Friday evening. Winds
will strengthen Friday night as the trough moves through. In the
mountains and on adjacent desert slopes...wind gusts of 45 to 65 miles per hour are
likely with local gusts of 70 miles per hour or greater in the wind-prone
areas. Winds will slowly weaken Saturday afternoon...diminishing
Saturday night.

Precipitation-wise...isolated light showers may begin as early as
Friday afternoon over the northern mountains...becoming more
widespread and increasing in intensity Friday night. Precipitation
amounts will be variable west of the mountains...but generally less
than one-quarter inch. Strong west winds will aid in orographic lift
along the coastal mountain slopes where rainfall totals around 0.50
to 0.75 inches are possible. Local amounts near one inch are
possible along the favored coastal slopes. Less than one-tenth inch
is expected in the deserts. There is a slight chance of
thunderstorms Friday night into early Sat morning. The best instability
will be over San Bernardino County where 500 mb temperatures fall to around
-23 to -27c. Any thunderstorms that develop could produce small hail
and locally heavy rainfall. Showers will taper off in most areas by
late Saturday morning...though a few showers may linger along the
Riverside and San Diego County coastal slopes into Saturday
afternoon. The snow level is expected to lower to between 4500 and
5500 feet by Sat morning...with 2-4 inches of snow possible above 5500
feet. Less than one inch of snow is expected above 5000 feet in the San
Diego County mountains.

The trough quickly exits late Sat with dry northwest flow aloft on Sunday
for minor warming and fair weather. A high pressure ridge gradually
builds in from the west next week with warmer weather and mostly
sunny skies prevailing. A cold surface high over the inter-mountain west
will bring periods of offshore flow...bringing additional warming
west of the mountains. Highs in the 80s and 90s will prevail at the
lower elevations...including the beaches...Tuesday and Wednesday. Highs in the
mountains will generally be in the middle 60s to middle 70s. Minor cooling
along the coast Thursday as onshore flow returns with warm conditions
continuing inland.

&&

Aviation...
250300z...coast/valleys...stratus...with bases around 1500 feet mean sea level
and tops to 2000 feet mean sea level...will develop along the coast this
evening...and spread around 30-40 sm inland by middle Friday morning. A
coastal eddy will help stratus tops and bases lift around 500 feet
overnight. Visible will lower to 2-4 sm br where low clouds near higher
terrain. Stratus will become scattered Friday afternoon...then broken/overcast Friday
evening..with slightly higher tops and bases.

Mtns/deserts...few/sct clouds at or above 20k feet with unrestricted visible
through Friday evening. Southwesterly winds of 25 to 35 knots...with
gusts to 60 knots will increase over mountains and Desert Mountain slopes Friday
evening...with windy conditions continuing through Sat.

&&

Marine...

No marine issues through midday Friday.

Friday afternoon through Sat...westerly wind gusts around 30 knots will
develop over the coastal waters...accompanied by a steep west-northwest swell
to around 10 feet. Winds and seas will create conditions hazardous for
small craft during this period. A Small Craft Advisory remains in
effect for Friday evening through Sunday morning. Winds will
decrease Sunday afternoon.

A 3-4 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 Sat-sun. Slightly lower surf is forecast for San
Diego County beaches...however strong longshore and rip currents are
likely.

&&

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

&&

Sgx watches/warnings/advisories...
California...Winter Weather Advisory from 8 PM Friday to 11 am PDT Saturday
for the Riverside County mountains...San Bernardino County
mountains.

High wind watch from Friday evening through Saturday evening
for the apple and Lucerne valleys...Coachella Valley...
Riverside County mountains...San Bernardino County
mountains...San Diego County deserts...San Diego County
mountains.

Pz...Small Craft Advisory from 5 PM Friday to 11 am PDT Sunday for
the coastal waters from San Mateo Point to the Mexican
border and out 30 nm...waters from San Mateo Point to the
Mexican border extending 30 to 60 nm out including San
Clemente Island.



&&

$$

Public...sunset
aviation/marine...jjt