Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 201244
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
444 AM PST Fri Jan 20 2017

.SYNOPSIS...
A very stormy pattern will continue across Southern California
through Monday. Heavy precipitation and strong winds are expected
today, along with a chance of thunderstorms near the coast. The
storm moves out Saturday. The next storm arrives Sunday, bringing
heavy precipitation and strong winds. Showers will continue Monday
with lower snow levels. Lingering showers Tuesday will wrap up the
wet pattern. Dry weather arrives Wednesday and Thursday as high
pressure and offshore flow develop.

&&

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

Intermittent light rain this morning will continue early this
morning as the next wave of rain moves down the coast into the
region. Expect winds and rain intensity to pick up during the day
and peak this afternoon as a front moves through the region. Winds
will shift from southerly to westerly. Thunderstorms are possible
along the front most likely near the coast this afternoon and
evening. Rainfall rates will be highest with areas of urban
flooding and localized flash flooding almost certain, particularly
if bursts of heavy thunderstorms get into the mix. Convective
bands or squalls are possible and could produce severe damaging
winds. Meanwhile snow will pile up above 5000 feet with no let
up. For details on mountain snow and winds, consult the winter
storm warning. For details on heavy rain and threat of flooding,
look at the flash flood watch. And for the story on the strong
winds, review our high wind warning. The jet stream will lift out
Saturday morning taking most of the showers with it, although
isolated showers could continue in the mountains. Winds will
decrease rapidly Saturday as well. Some break in the action is
expected Saturday afternoon through Saturday night. Latest model
guidance suggests a later start to the rain expected with the next
storm on Sunday. While we expect rain to pick up in Orange County
Sunday morning, it might wait for Sunday afternoon around San
Diego. Nevertheless, an atmospheric river is pointed right at
Southern California and precipitation looks heavy Sunday afternoon
through Sunday night. This heavy band will be relatively warm so
rain will fall on new snow in the mountains below 7500 feet. The
cold core of the trough settles over the region Monday for showers
to continue and snow levels to plummet down to 3500 feet. It
could also destabilize the atmosphere enough for thunderstorms,
but confidence is not high enough yet to forecast them. Most of
the showers end Monday night, but there is one more northerly wave
that drops down into the region Tuesday. This has little moisture,
but will provide enough energy to keep some showers going. Finally,
the low pressure trough moves eastward and high pressure slowly
builds aloft. Offshore pressure gradients begin to tighten
Wednesday and Thursday for some offshore winds and much drier
weather. The warming trend looks slow and gradual.

&&

.AVIATION...
201100Z...Coast and Valley...Widespread rain and strong winds today
with CIGS BKN-OVC010-020. Scattered thunderstorms this afternoon and
evening with strong cells likely. CIGS lowering to OVC005-010 under
the heavier rain bands and thunderstorms. Vis 2-4SM in widespread
Rain and Fog. Vis lowering to 1/2SM under heavier rain bands and
thunderstorms. Sustained winds 20-30 kt w/ gusts to 40 kt between 18-
23Z impacting all coastal and valley TAF sites. Isolated Strong to
severe thunderstorms possible between 18Z-02Z with squalls to 50
kt and funnel clouds. Pcpn activity diminishing aft 06Z this evening.

Mountains and Deserts...SW to W wind gusts of 50-70 kt over the
mountains and down the desert mountain slopes and into adjacent
deserts today. Severe UDDFS will be possible on the lee side of the
mountains through the period. Mountains obscured in clouds and heavy
pcpn at times today. Pcpn activity diminishing aft 06Z this evening.

&&

.MARINE...
Several strong Pacific fronts moving across the region will continue
unsettled conditions through Tuesday. A Gale Warning continues
through Saturday. Another Gale Warning may be necessary for Monday
with the passage of another strong Pacific front. See the Gale
Warning message (LAXMWWSGX) currently in effect for additional
details. A Marine Weather Statement has also been issued for this
afternoon and evening for the potential for strong thunderstorms
over the coastal waters, which could contain gusts to 50 kt,
frequent downpours and lightning, large hail, and waterspouts.

&&

.BEACHES...
A High Surf Warning in effect through Tuesday. Large damaging surf
is likely later today through Saturday, and again Monday into
Tuesday. Coastal flooding and beach erosion possible as highest sets
to 16 ft occur tonight through Saturday coincident with times of
high tide. High tide is 4.6 ft at La Jolla at 435 AM Saturday.
The high surf and strong rips will make swimming conditions very
dangerous for all swimmers. High Surf will gradually diminish by the
middle of next week.

&&

.HYDROLOGY...
A wet and stormy pattern will continue today and get a boost
this afternoon with heavy rain rates and a chance of
thunderstorms. Rain rates are almost certain to create urban
flooding problems and may produce some flash floods. Check the
flash flood watch for details. Showers taper off tonight and
Saturday. Sunday afternoon and night persistent heavy rain is
expected with rain rates capable of flooding. Snow levels will be
around 5000 feet today. On Sunday snow above 7500 feet then
dropping to 3500 feet by Monday afternoon. Grand totals for this
wet period from today through Tuesday:

Coast and Valleys: 2-5 inches
Mountains: 4-10 inches, with isolated 12+ inches
Deserts: 0.50-2 inches

&&

.SKYWARN...
SKYWARN IS ACTIVATED TODAY through the evening. Skywarn will
likely be activated Sunday through Monday. The main threats are
flooding, damaging winds, heavy snow, and high surf.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 6 AM PST Saturday for Riverside
     County Mountains-San Bernardino County Mountains-San Diego
     County Mountains.

     Flash Flood Watch through this evening for Orange County Coastal
     Areas-Orange County Inland Areas-Riverside County Mountains-
     San Bernardino County Mountains-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Mountains-San Diego County
     Valleys-San Gorgonio Pass Near Banning-Santa Ana Mountains
     and Foothills.

     High Wind Warning until 10 PM PST Saturday for San Diego County
     Deserts.

     Wind Advisory until 10 PM PST Saturday for Apple and Lucerne
     Valleys-San Gorgonio Pass Near Banning.

     High Wind Warning until 10 PM PST this evening for Orange County
     Coastal Areas-Orange County Inland Areas-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Valleys-Santa Ana Mountains
     and Foothills.

     Wind Advisory from 10 AM this morning to 10 PM PST Saturday for
     Coachella Valley.

     High Surf Warning until 10 PM PST Tuesday for Orange County
     Coastal Areas-San Diego County Coastal Areas.

PZ...Small Craft Advisory until 10 AM PST this morning for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm-Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

     Gale Warning from 10 AM this morning to 4 PM PST Saturday for
     Coastal Waters from San Mateo Point to the Mexican Border
     and out to 30 nm-Waters from San Mateo point to the Mexican
     Border Extending 30 to 60 nm out including San Clemente
     Island.

&&

$$

PUBLIC/HYDROLOGY...MM
AVIATION/MARINE/BEACHES...Brotherton


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