Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 161659
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
859 AM PST Mon Jan 16 2017

.SYNOPSIS...
High pressure aloft will continue dry weather through Wednesday
with weak offshore flow today and Tuesday, becoming onshore
Wednesday. For Thursday into early early next week...a series of
Pacific storm systems are expected to bring periods of strong
gusty winds and precipitation...some of of it heavy at times with
snow in the mountains.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

satellite imagery early this morning shows a mix of high and lower
clouds over SW CA. The 12Z Miramar sounding showed the marine layer
depth had increased to around 4500 FT. Surface pressure gradients
were trending back offshore once again at around 7 MBS from SW NV
to KSAN. At 8 AM PST...peak wind gusts reported were under 25 MPH.

Warmer and dry today as clouds thin. No changes to previous
forecast.

From previous discussion...

A large coastal eddy over the Southern California coastal waters
will dissipate today. Thar marine inversion is near 4000 feet
with satellite imagery showing areas of low clouds extending onto
the lower coastal mountain slopes.

High pressure aloft over California will continue dry weather into
Wednesday. Weak offshore flow will bring periods of gusty north
to northeast winds below the Cajon Pass and along the coastal
slopes of the Santa Ana Mountains into Tuesday...strongest late
tonight into Tuesday morning with peak gusts to around 50 mph.
high temperatures will warm to slightly below average on
Tuesday...then cool slightly for Wednesday as onshore flow
returns.

&&

.LONG TERM (Wednesday night through Sunday)...
A strong Pacific jet stream will direct a series of storm systems
into and through Southern California for late Wednesday night into
early next week in quick succession. There remain some
model differences in the timing and intensity of each storm. The
first storm is expected for late Wednesday night and Thursday...a
second for Friday...a third for Saturday...and a fourth for late
Sunday night and Monday with showers continuing into Tuesday. The
06Z GFS has trended toward the ECMWF and Canadian models with the
timing for the system for late Sunday night and Monday. The
current guidance has the Friday system stronger than those for
Thursday and Saturday with the storm for late Sunday night and
Monday the strongest of the four. That could change with later
guidance. Precipitation could be heavy at times...especially
Friday and Monday with periods of strong gusty winds with the
passage of each system. Please refer to the hydrology section
below for the precipitation potential for this series of storms.

&&

.AVIATION...
161625Z...Patchy BKN stratus over the coast and valleys, with bases
2500-3000 ft msl, tops 4000-4500 ft msl and local vis AOB 5 sm, will
likely clear out through 2000 UTC, with otherwise SCT-BKN clouds AOA
12000 ft msl and P6SM vis through 17/0000 UTC. 17/0000-1500
UTC...patchy BKN stratus may develop within 10 SM of the central and
southern San Diego county coast, possibly impacting KSAN and KCRQ,
but confidence is low. Bases and tops would be around 1000 ft msl
and 1500 ft msl respectively. Otherwise, FEW clouds AOA 20000 ft msl
and vis P6SM.

&&

.MARINE...
A Pacific storm will bring rain, strong west to northwest winds
gusting to 25 kt and large seas of 7-10 feet on Thursday, mainly in
the outer waters. These conditions would be hazardous to small
craft. The storm system that follows mid Friday into Saturday has
the potential for winds reaching near gale force in the inner and
outer waters, in addition to combined seas near 15 feet.

&&

.BEACHES...
A moderate sized long-period west-northwest swell from around 285
degrees will peak today and lower Tuesday. The swell will create
surf of around 3-6 ft with local 7 ft sets and strong rip currents.
However, widespread high surf is not expected.

From Thursday through next weekend, a couple short to moderate
period large west-northwest swells will impact the coast. The
highest surf will occur over the weekend when a very large
short-period WNW swell combines with a moderate sized WNW long-
period swell. During the peak of the swell event, surf could be
large enough (sets possibly reaching 15 ft) to cause minor damage,
minor coastal flooding and moderate beach erosion.

&&

.HYDROLOGY...
For late Wednesday night through early next week...a series of
Pacific storms are expected to bring significant precipitation to
Southern California. There remain some differences in the timing
and intensity of each storm. The first storm is expected for late
Wednesday night and Thursday...a second for Friday...a third for
Saturday...and a fourth for late Sunday night and Monday with
showers continuing into Tuesday. The current guidance has the
Friday system stronger than those for Thursday and Saturday with
the storm for late Sunday night and Monday the strongest of the
four. That could change with later guidance.

Some very preliminary forecast rainfall totals for Thursday
through Tuesday of next week...

Coast...........2 to 3 inches.
Valleys.........3 to 5 inches.
Mountains.......4 to 8 inches.
Upper deserts...1 to 2 inches.
Lower deserts...0.5 to 1 inch.

Local amounts of 12+ inches are possible in the mountains...
especially on the lower coastal slopes of the San Bernardino
County mountains. Flooding potential could increase markedly by
Monday if these storms develop as currently forecast.

Snow levels will lower to around 4000 feet at times. Snowfall of 4
feet or more is possible on the higher peaks with 2 feet or more
above 6500 feet.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.

&&

$$

PUBLIC...JAD
HYDROLOGY...17
AVIATION/MARINE/BEACHES...Harrison



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