Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 190548 AAA
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
945 PM PST Sun Feb 18 2018

.SYNOPSIS...
Onshore flow will be increasing tonight, becoming strong and gusty
over the mountains and deserts as a cold low pressure trough drops
south into the Great Basin. Scattered, light rain and snow showers
will pop over and west of the mountains late tonight into Monday as
the marine layer builds. Expect the coldest days of the winter so
far on Monday and Tuesday. Dry and a little warmer for Wednesday and
Thursday. Then cooler again into Friday, with a chance for some more
scattered showers as another cold low pressure system drops into the
Great Basin from the north. Dry and a little warmer into next
weekend as temperatures edge back toward average.

&&

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

...Evening Update...

 Rain showers are developing offshore, likely to
move onshore after 10 pm. Most of this activity will be quite light
as it moves inland through the night. Snow showers will be likely in
the mountains late tonight but again on the light side. With
temperatures already down into the mid 40s in the high desert, there
is a slight chance of seeing some snow flurries by Monday morning
there as well once the cooler air is ushered in by the vigorous
trough which will be dropping through California overnight. No
significant changes were needed to the forecast this evening.

...Remainder of previous discussion...

A longwave trough will dive into the Great Basin on Monday, grazing
SoCal with strong onshore winds and scattered light precipitation.
It will also bring the coldest air of the season, plunging maximum
temps on Monday into the 15 to 20 degrees below normal range. given
the extended period of well above normal temps this winter, it will
be a profound change.

This wave is actually the beginning of a more sustained cooler
weather pattern for the SoCal as the longwave is maintained for
sometime in the model runs. Various shorter wavelength disturbances
will periodically drop into the longwave, creating gusty onshore
flow over the coastal waters, mts and deserts, and chances for light
precip. So for the foreseeable future, daytime temperatures will
be mostly below average.

A variety of Warnings and Advisories are in effect from frost/freeze
to wind and winter conditions. Please visit our webpage for more
detail on all of these. Of most significance will be the strong
westerly winds late tonight into Monday. Gusts over 70 MPH are
expected on the upper desert slopes and ridge tops, while on the
desert floor, it will be breezy, but potentially damaging gusts look
to be more isolated and near the foothills late tonight into Monday
morning. windy conditions are also expected for coastal San Diego
County on Monday. Precipitation will be light and scattered, but it
will be cold enough so that some light snow accumulations are
forecast above 4000 FT. Freezing conditions on the passes, could
create a hazard to travelers.

As this system moves east, another, weaker trough slips south across
the area midweek with little weather. Temps will moderate some, then
a stronger disturbance drops south for Friday. this one could
generate more light showers, and gusty winds over the mts/deserts/
coastal waters. Slightly warmer and dry into the weekend, then both
the 12Z GFS/ECMWF runs are advertising a stronger system early next
week. Who knows, we may be able to salvage some precip before the
end of the month.

&&

.AVIATION...
190515Z...Mostly BKN-OVC clouds with bases 2000-4000 ft MSL will
prevail through Monday afternoon from the mountains to the coast,
with scattered -SHRA, most frequent 07Z-13Z, plus scattered -SHSN in
the mountains. Higher terrain will be obscured, with tops to 8000 ft
MSL possible, but at TAF sites, most vis will remain above 5 miles.
By Monday evening, most areas will have SCT clouds, generally above
3000 ft MSL.

Southwest to west winds 25-35 kt with gusts to 55 kt will continue
to spread over the mountain crests and desert mountain slopes
tonight with these strong winds continuing through Monday afternoon.
Areas of west winds 20-30 kt will occur near the coast Monday and
will likely bring gusts around 30 kt at KSAN at times.

&&

.MARINE...
West-northwest winds will increase to 20-30 kt tonight and continue
through Monday night, with gusts 35 to 40 kt possible in the outer
waters Monday morning. Combined seas of 9-13 ft with steep waves are
likely Monday through Monday evening in the outer waters with 7-11
ft in the inner waters. Conditions will improve Tuesday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 6 PM this evening to 10 PM PST
     Monday for Riverside County Mountains-San Bernardino County
     Mountains-San Diego County Mountains.

     Wind Advisory from 2 PM this afternoon to 6 PM PST Monday
     for Coachella Valley-San Diego County Deserts-San Gorgonio
     Pass Near Banning.

     High Wind Warning from 2 PM this afternoon to 6 PM PST Monday
     for Apple and Lucerne Valleys.

     Frost Advisory from 10 PM Monday to 9 AM PST Tuesday for San
     Diego County Valleys-San Gorgonio Pass Near Banning.

     Wind Advisory from 8 AM to 6 PM PST Monday for San Diego County
     Coastal Areas-San Diego County Valleys.

     Frost Advisory from 10 PM Tuesday to 8 AM PST Wednesday for San
     Bernardino and Riverside County Valleys-The Inland Empire.

     Freeze Warning from 10 PM Monday to 9 AM PST Tuesday for San
     Bernardino and Riverside County Valleys-The Inland Empire.

PZ...Gale Warning from 10 PM this evening to 6 AM PST Tuesday for
     Waters from San Mateo point to the Mexican Border Extending
     30 to 60 nm out including San Clemente Island.

     Small Craft Advisory from 10 PM this evening to 6 AM PST Tuesday
     for Coastal Waters from San Mateo Point to the Mexican
     Border and out to 30 nm.

&&

$$

PUBLIC...jad/jmb
AVIATION/MARINE...Maxwell



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