Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 192128
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
128 PM PST Mon Feb 19 2018

.SYNOPSIS...
A few more isolated rain and snow showers could develop late this
afternoon or evening, otherwise clear to partly cloudy and much
cooler overnight with frost and freezing conditions in the valleys.
The low pressure trough responsible will move east on Tuesday, but
several more weaker systems will slide south over the region during
the latter half of the week, keeping temperatures below average, and
possibly sparking more periods of scattered, light showers. The
winds will continue quite gusty through this evening, then weaken
late tonight. Continued cool on Tuesday, followed by slight warming
midweek. Dry and a little warmer next weekend.

&&

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

At midday...Satellite imagery showed fair weather cumulus over San
Diego County, and developing clouds to the NW over the mts of LA/San
Bernardino and Orange Counties, otherwise it was clear. Surface
pressure gradients were relaxing a bit to the deserts, but were
still around 9 MBS KSAN to SW NV. This was sufficient to support
breezy conditions over much of the region with strong gusts of 50
MPH or more over the San Diego County Mts. A new storm precip
summary has been posted to our website. Snow reports were all one
inch or less.

Breezy conditions will continue into the evening most areas, while
over the mts/deserts, gusts will still be of Advisory strength. Any
high wind reports should be few, and confined to the windiest spots
in the San Diego County Mts if anywhere. There will be another shot
at some scattered rain and snow showers late today and this evening
as the last disturbance rotates through the trough, then skies
should clear away and winds drop off, especially in wind sheltered
spots. This will allow the temps to fall to the freezing
mark or below in the valleys. Frost and Freeze Advisories/Warnings
are in effect. the Winter Weather Advisory remain in effect over the
mts this evening due to the strong winds. cold, and additional snow
showers.

The cold low pressure trough that has settled into the Great Basin
will begin to lift out later tonight and Tuesday. Winds will
gradually decrease overnight, allowing sfc temps to fall rapidly.
this has prompted frost advisories and freeze warnings in the
valleys. It will start out much colder tomorrow morning, but with
plenty of sun expected, temps should warm back into the upper 50s
and lower 60s west of the mts.

Any warming will be modest as both the GFS/ECMWF model runs are
holding the longwave trough position over the West with strong high
pressure over the SE U.S. There is no shortage of disturbances lined
up to drop into the trough, with the next on possibility
influencing our weather as soon as Wednesday. Low POPS are in the
forecast by afternoon/evening, increasing into Thu with both
12Z model runs showing precip on SoCal. Once again, this type of
system will not have sufficient moisture and instability for any
heavy precip, and given the shallow depth of the moist layer,
most would fall along and west of the mts.

Another break comes next weekend as a stronger wave appears to
gather strength and drop south off the PacNW coast. There are
considerable model differences in the deepening and track of this
wave, but both the GFS/ECMWF suggest it will be able to generate
precip over SoCal mid next week with a better fetch of moisture.


&&

.AVIATION...
192115Z...Coast and Valleys...SCT-BKN clouds with bases at or above
3500 feet MSL and unrestricted vis through 06Z Tue. Mostly clear
with unrestricted vis after 06Z Tue. Areas of west winds 20-30 kt
will occur near the coast through about 00Z Tue. Winds weaken after
00Z Tue.

Mountains and Deserts: SCT-BKN clouds on coastal slopes through this
evening will bring local terrain obscuration between 3500-7000 feet
MSL. Scattered clouds at or abv 5000 feet msl in the desert.
Southwest to west winds 25-35 kt with gusts to 55 kt will continue
over the mountain crests and some of the desert mountain slopes
through this evening. This will cause mdt-strong up/downdrafts over
and east of the mtns. Occasional vis reductions to 3-5sm in blowing
dust and sand for some areas.

&&

.MARINE...
Northwest winds with gusts 25 to 30 kts and hazardous seas will
continue through tonight. See the Marine Weather Message and Coastal
Waters Forecast for details. No hazardous marine conditions are
expected Tuesday into Thursday, but hazardous winds and seas are
likely again late Thursday and Friday.

&&

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


&&

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

     Wind Advisory until 6 PM PST this evening for Coachella Valley-
     San Diego County Deserts-San Gorgonio Pass Near Banning.

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

     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 this evening to 9 AM PST Tuesday for
     San Bernardino and Riverside County Valleys-The Inland
     Empire.


PZ...Small Craft Advisory until 6 AM PST Tuesday 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...jad
AVIATION/MARINE...PG



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