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000
FXUS66 KSGX 191058
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
258 AM PST Tue Feb 19 2019

.SYNOPSIS...
Dry weather with well below average temperatures will continue
into Wednesday morning with cold nights and areas of frost in the
valleys and lower deserts. For Wednesday afternoon into Friday,
another cold low pressure system from the north will bring showers
with low snow levels and with strong and gusty west to northwest
winds in the mountains and deserts. Heavy snowfall is possible in
the higher mountains. Dry and a little warmer for the weekend.
Small chances for light precipitation could return for Sunday
night and Monday.

&&

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

.SHORT TERM (Today through Thursday)...
The low pressure system that brought showers on Sunday into Sunday
night and again Monday afternoon is over Arizona and moving
eastward. Skies are mostly clear across southern California with
weak northerly offshore flow. The rest of tonight into early this
morning is expected to be the coldest morning for many locations
with low temperatures in much of the valleys in the upper 20s to
mid 30s. With the offshore flow, gusty north to northeast winds
will provide some mixing in portions of the Inland Empire and near
the coastal foothills of the Santa Ana Mountains. When and where
mixing occurs in the Inland Empire, temperatures will rise to
around 40 degrees. Tonight is expected to be the coldest night for
the lower deserts with a frost advisory extended to portions of
the lower deserts for tonight into Wednesday morning. Well below
average high temperatures will continue today.

Another cold low pressure system from the north will bring more
showers with low snow levels for Wednesday afternoon into Friday
along with a slight chance for thunderstorms for Thursday
afternoon and early evening. The slight chance of thunderstorms
has been added to the forecast for Thursday afternoon and early
evening as very cold air aloft will help to destabilize the
atmosphere with 500 mb temperatures colder than -30 C.

In Orange and southwestern San Bernardino Counties, rainfall
could range from one tenth to one quarter of an inch near the
coast, to one half to one inch in the mountains. For San Diego and
western Riverside Counties, rainfall could range from one third
to one half inch near the coast to 1.00 to 1.50 inches in the
mountains with local amounts to around 2 inches. Amounts in the
deserts will mostly be less than one tenth inch.

Snow levels will rise to around 4000 feet for Wednesday afternoon
and evening, then fall to 2500 to 3000 feet for Thursday, and 2000
to 2500 feet for Thursday night into Friday with local snow levels
around 1500 feet. Winter weather advisories and warnings may be
needed for the mountains for Wednesday night into Thursday night
and possibly also for the high desert and portions of the Inland
Empire.

&&

.LONG TERM (Thursday night through Monday)...
Showers will continue into Thursday, then decrease from the north
overnight into early Friday morning. There are small chances of
showers continuing into Friday afternoon with cold air aloft and
residual moisture. Saturday into Sunday is expected to be dry and
a little warmer.


For Sunday and Monday, there has been a slight westward shift with
the next low pressure system moving southward into the western
states. This might allow for some entrainment of Pacific moisture
with small chances for light precipitation returning for Sunday
night and Monday.

&&

.AVIATION...
191000Z...Mostly clear skies today and tonight. Local offshore winds
northeast gusting 25-35 kt in mountain foothills through 18Z today.

&&

.MARINE...
Onshore winds and seas will increase Wednesday, leading to hazardous
conditions as a storm system arrives. Strong winds and high seas
will continue into Thursday night before diminishing. There is also
a slight chance of thunderstorms Thursday afternoon.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory until 9 AM PST this morning for San Bernardino
     and Riverside County Valleys-The Inland Empire-San Diego
     County Valleys.

     Frost Advisory from 10 PM this evening to 9 AM PST Wednesday for
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Valleys.

     Frost Advisory from midnight tonight to 9 AM PST Wednesday for
     Coachella Valley-San Diego County Deserts.

PZ...NONE.

&&

$$

PUBLIC...17
AVIATION/MARINE...MM