Frost Advisory 1, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
832 PM PST Tue Feb 5 2019

.SYNOPSIS...
Showers will continue tonight, with greatest amounts in San Diego
County. The snow level will fall to around 2500 feet overnight, with
several inches of snow in the mountains. Fair but chilly weather
will occur Wednesday with slight warming Thursday and Friday. Frost
will occur in many valley locations Wednesay night. A trough of low
pressure over the western United States will bring a couple of waves
through southern California along with chances of precipitation
Saturday and Monday.

&&

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

Forecast updated to add some light snowfall to the high deserts
tonight. A new Rain and snowfall update (four day total) was issued
at 8 PM PDT and is headlined on our web page.

Radar, (including KSOX now) was showing widely scattered, mostly
light showers drifting from west to east at 8 PM PST. A more
continuous band was noted over the high deserts. Cold, cyclonic flow
aloft will maintain some showers much of the night but hires models
show only light accumulations. The 00Z Miramar sounding had dried to
a PW of 1/2 inch, but had a moist layer up to 8K FT. Below 8K was
unstable and with a 15 KT west wind below 5K FT. This profile
supports some island banding, which should be primarily from the NW
once the tough passes in a few hours. So if showers are island
enhanced, it would most likley affect southern San Diego County.

Surface pressure gradients were beginning to relax KSAN to the
deserts at 6-8 MBS, but many mountain sites still had westerly wind
gusts 40 to 48 MPH. Based on mtn observations, it appears the snow
level had fallen to between 3500 and 4000 FT in San Diego County by
7:30 PM. Showers were few and far between at 8 PM PST, so any
accumulating snowfall is light and scattered. The latest WRFEMS and
HRRR runs continue showers through the night for mainly San Diego
County, and end them farther to the north around midnight. Given the
wind, snow showers, and low snow levels, the Winter Storm Warning
will remain in place until expiration. Models suggest another inch
or two of snow could fall above 3500 FT, and lower to the sfc over
the high deserts, and around 2500 FT on the coastal foothills in San
Bernardino County.

From previous discussion...

Models are consistent with ending the last bit of the precipitation
by 4-5 AM Wed, and Wed will be partly cloudy with the continued
onshore flow in San Diego County and sunny elsewhere. 850 MB temps
do not start to recover until Wednesday night, so it will be quite
chilly across the region, with lower elevation highs mostly in the
50s to near 60 Wednesday. Some weak ridging will bring warming
Thursday and Friday, though temperatures will remain below normal. A
trough of low pressure will reestablish itself over the West Coast
or a little bit inland, and a couple of short waves could bring
light amounts of precipitation Saturday and/or Monday. Models are
inconsistent with projections after next Monday, though pretty much
all projections keep our window open for future precipitation,
especially the second half of next week.

&&

.AVIATION...
060420Z...ISO-SCT showers will continue through tonight for all
areas but the low desert. SCT-BKN cloud layers 3500-7000 ft MSL
gradually clearing by 15Z. Coastal mountain slopes will remain
partially obscured in clouds/precip overnight. After 15Z...a few
high clouds and unrestricted vis.

West winds with sfc gusts 25-45 kt will continue through about 10Z
along the ridges and desert mountain slopes, producing locally MDT-
STG up/downdrafts over and east of the mtns. Rotors are likely near
KPSP. Winds gradually weakening Wednesday morning.

&&

.MARINE...
Northwest winds with gusts 20 to 25 kts will continue through early
Wednesday in the inner waters, and through Wednesday evening in the
outer waters. A Small Craft Advisory is in effect.

&& &&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 4 AM PST Wednesday for Riverside
     County Mountains-San Bernardino County Mountains-San Diego
     County Mountains.

PZ...Small Craft Advisory from 1 PM this afternoon to 8 PM PST
     Wednesday for Waters from San Mateo point to the Mexican
     Border Extending 30 to 60 nm out including San Clemente
     Island.

     Small Craft Advisory from 1 PM this afternoon to 4 AM PST
     Wednesday for Coastal Waters from San Mateo Point to the
     Mexican Border and out to 30 nm.

&&

PUBLIC...10/Maxwell
AVIATION/MARINE...SS