Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 181317
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
517 AM PST Sun Feb 18 2018

.SYNOPSIS...
A cold low pressure system from the north will bring much cooler
weather...scattered mostly light showers along and west of the
mountains for late this afternoon into Monday evening...and
periods of strong gusty west winds in the mountains and deserts
for this afternoon through Monday. Dry and a little warmer for
Wednesday and Thursday. For Thursday night and Friday...another
cold low pressure system from the north could bring additional
mostly light showers. Drier and a little warmer for next weekend.

&&

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

The coldest weather of the winter for Southern California is
upcoming and will continue through the end of the month.

A cold low pressure system centered along the coast of southern
British Columbia early this morning will move southward through
the western states through Monday. Onshore flow will strengthen
today with the strongest onshore flow expected for tonight and
Monday. Coastal...valley...and mountain areas will be around 10
degrees cooler today than Saturday. Winds will strengthen for the
mountains and deserts today with the strongest winds for this
afternoon into Monday. Stronger winds will develop over the
coastal waters late tonight and spread into coastal and valley
areas of San Diego County on Monday.

Much cooler air will spread into Southern California for Monday
and Tuesday with high temperatures for Monday 15 to 25 degrees
below average with high temperatures Tuesday a few degrees
warmer.

This low pressure system will bring scattered mainly light
showers along and west of the mountains with the greatest coverage
for late tonight through early Monday. Rainfall is expected to
range from one tenth inch or less at the coast to one quarter to
one third inch in the mountains with locally greater amounts. The
snow level will lower from around 6000 feet late today to 3000 to
3500 feet for Monday through Monday evening with a few inches of
snowfall possible above 4000 feet.

Cold nights will for Monday and Tuesday nights with temperatures
falling to near freezing in the valleys with areas of frost. Drier
and a little warmer for Tuesday into Thursday with north to
northwest flow aloft.

The global models continue to bring additional shortwaves
southward along the west side of the longwave trough parked over
the western states with the expected timing and intensity
differences. One of these could bring additional chances for
mostly light showers for late Thursday into Friday with next
weekend drier and a little warmer but with continued below
average temperatures.

The longwave trough axis could shift westward a little for the
week of the 25th which would maintain the cooler than average
temperatures...but increase the precipitation prospects somewhat.

&&

.AVIATION...
181030Z...Confidence in stratus impacting coastal aerodromes this
morning is decreasing. Patches of low clouds currently near LA
County may push south and affect KSNA, but chances look low at this
time. Any low clouds that develop will have bases around 500 ft MSL
and tops near 1000 ft MSL. VIS could also lower to 1-3 sm BR where
low clouds near higher terrain. Otherwise, occasional high clouds
above 20000 ft MSL will continue through this afternoon. Clouds will
increase rapidly this evening from the mountains west to the coast,
with bases mostly 2000-3000 ft MSL with higher terrain obscured.
SHRA could develop late tonight through Monday morning.

&&

.MARINE...
No hazardous weather is expected through this afternoon. West-
northwest winds will increase to 20-35 kt tonight and continue
through Monday night, with local gusts to 40 kt possible in the
outer waters Monday morning. A Gale Warning has been issued for the
outer waters and a Small Craft Advisory remains in effect for the
inner waters from 10 PM this evening through 6 AM Tuesday. Combined
seas of 7-13 ft with steep waves are likely through the period.
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...17
AVIATION/MARINE...JJT



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