Frost Advisory 5, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
859 PM PST Mon Feb 13 2023

.SYNOPSIS...
A cold low pressure system will dive into the Great Basin on
Tuesday, accompanied by a strong jet stream over California. This
will bring strong westerly winds to much of the region, along with
mostly light rain and snow showers from the mountains westward.
Upslope onto the coastal slopes should help generate the heaviest
amounts of precipitation there. The west winds will be exceptionally
strong and potentially damaging along the ridges and desert slopes
and foothills of the San Diego County mountains. Winds will weaken
and turn north to northeast on Wednesday, favoring some warming and
drying. Freezing temperatures are anticipated Wednesday and Thursday
mornings in the wind-sheltered valleys, but the days will moderate
under mostly sunny skies.

&&

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

Radar shows very weak echoes drifting inland off the coastal waters
this evening. Some of these were producing drizzle and spotty light
rain. This activity should increase slowly overnight, based on the
latest HRRR and WRF guidance. Any accumulations will remain very
light though. Surface pressure gradients were already accelerating
onshore at 8 PM PST, and so were the winds, peaking with gusts of 50
to 60 MPH near the passes. A Zone Forecast update was issued earlier
to add a chance for some light showers this evening west of the
mountains, to add a High Surf Advisory/ Beach Hazard statement for
San Diego/Orange Counties, and increase the winds. No other updates
are planned this evening.

From previous discussion...

The next wave in an active and amplified weather pattern will
dive into the Great Basin late tonight and Tuesday morning. The
primary impact from this system will be the strong westerly winds
blowing across the mountains and into the deserts, where High Wind
Warnings are now in effect starting this evening and lasting
through Tuesday evening. ECMWF EFI guidance suggests a majority of
ensemble members forecasting sustained winds and wind gusts
higher than the model climate, with SOT guidance favoring
significantly strong winds over portions of the mountains and
deserts. 700mb wind speeds, per the ECMWF model, ranging from
60-70kts will blow across the peninsular mountain ridgelines. This
is also supported by the CANSAC WRF depicting wind speeds
approaching 80mph in the desert foothills, raising concerns for
areas of blowing dust. SOT guidance also favors significant winds
over the coastal waters impacting the immediate coastline, where
Wind Advisories are also in effect from Tuesday afternoon through
Tuesday evening.

Precipitation impacts from this next system look to begin late
this evening and overnight, with most rain/snow tapering off late
Tuesday afternoon and evening. Snow levels generally start between
5500-6000 feet tonight, and then fall through Tuesday afternoon
when snow levels will range from around 4000 feet in the San Diego
County Mountains to as low as 2500 feet in the San Bernardino
County Mountains. Upsloping onshore flow will favor the coastal
mountain slopes for the heaviest precipitation, with localized
areas seeing precipitation totals of 0.30-0.60 inch occur. Areas
west of the mountains will receive less, generally under 0.25 inch
in most locations. Snowfall totals of 1 to 4 inches can be
expected for mountain communities above 4,000 feet in elevation.
With the combined impacts from snow and high wind, a Winter Storm
Warning has been issued from 06z Tue through 00z Wed for these
areas.

As this system departs to the east on Wednesday, colder and drier
air will filter into Southern California leading to cold morning
lows both Wednesday and Thursday morning. Wind-sheltered locations
will likely see frost develop, with potential for sub-freezing
lows in some isolated locations mainly in Riverside County between
the mountains and I-215. Winds will also shift to offshore flow
behind this system, favoring a brief round of Santa Anas on
Wednesday with the gustiest winds generally occurring below
mountain passes and through wind-prone canyons and valleys. This
also leads to a warming trend in daytime high temperatures,
warming a few degrees each day Wednesday through Friday. Despite
the warming trend, most locations will remain several degrees
cooler than seasonal normals through the weekend.

The next low pressure system approaches the California coast from
the northwest later this weekend. Differences in timing and track
of the 500mb low preclude any specific details regarding potential
precipitation and wind impacts. The general consensus track in EPS
guidance would favor similar impacts to last night’s storm which
favored the heaviest precipitation in San Diego County. The spread
in ensemble QPF guidance remains rather large, with EPS members
ranging from no precipitation at all to upwards of 1.2 inches in
24hrs starting on Saturday. Given the uncertainties, will keep
close to NBM guidance for this period.

&&

.AVIATION...
140415Z...Coast/Valleys... SCT-BKN low clouds 1500-3500 ft MSL.
Areas of light rain expected through 23Z Wed. Cigs will occasionally
lower to closer to 1000 ft MSL in areas of SHRA. After 14Z Tue west
winds increasing to 20-30 kt at KSAN, KCRQ and KSNA.

Mountains...Widespread clouds and RA/SN will obscure mountains
through Tuesday evening. Strong west winds 30-40 kt gusting 70-80
kt, locally to 90 kt. Strongest winds will be in the San Diego
County mtns. Winds will weaken from north to south after 00Z Wed and
become north/northeasterly.

Deserts...Strong northwest winds 20 to 30 kt gusting 40 to 50 kt
Tuesday afternoon and evening. Strongest winds will be in the High
Desert and the San Diego County desert. Areas of reduced visibility
in BLDU possible after 18Z Tue. Winds will weaken and quickly shift
north-northeast from north to south after 04Z Wed. -SHRA possible
after 00Z Wed.

&&

.MARINE...
A Gale Warning is in effect for both the Inner and Outer Waters
Tuesday and Tuesday night for WNW gales of 20-30 kt gusting 40-45
kt. Seas will build to 8 to 18 ft. The strong winds and short period
wind swell will make boating conditions extremely hazardous. The
strongest winds and highest seas are expected Tuesday evening.

&&

.BEACHES...
A west-northwest swell from 290 degrees will generate elevated to
high surf Tuesday and Wednesday. Surf of 7 to 10 feet expected in
San Diego County and surf of 4 to 7 feet is expected in Orange
County. Surf will peak late Tuesday afternoon and evening and
diminish into Wednesday. Surf in Orange County will fall below 5
feet by mid-Wednesday morning, with surf forecast to remain 5 to 6
feet in San Diego County into Wednesday afternoon and evening. Surf
will be highest in south San Diego County. Strong rip currents and
hazardous swimming conditions expected through Wednesday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory from 10 AM Tuesday to 2 PM PST Wednesday for
     San Diego County Coastal Areas.

     Wind Advisory from 2 PM to 10 PM PST Tuesday for Orange County
     Coastal Areas-Orange County Inland Areas-San Diego County
     Coastal Areas.

     High Wind Warning until 10 PM PST Tuesday for Apple and Lucerne
     Valleys-Coachella Valley-Riverside County Mountains-San
     Bernardino County Mountains-San Diego County Deserts-San
     Diego County Mountains-San Gorgonio Pass Near Banning.

     Winter Storm Warning until 4 PM PST Tuesday for Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Mountains.

     Beach Hazards Statement from Tuesday morning through Wednesday
     morning for Orange County Coastal Areas.

PZ...Gale Warning from 1 PM Tuesday to 3 AM PST Wednesday for Coastal
     Waters from San Mateo Point to the Mexican Border and out
     to 30 nm.

     Gale Warning from 7 AM Tuesday to 3 AM PST Wednesday for Waters
     from San Mateo Point to the Mexican Border Extending 30 to
     60 nm out including San Clemente Island.

&&

PUBLIC...10/Adams
AVIATION/MARINE/BEACHES...CO