Winter Storm Warning 1, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
917 PM PST Sun Feb 20 2022

.SYNOPSIS...
A change in the weather is in store for this week as a strong
trough of low pressure moves into California. Each day will be
progressively colder through Wednesday with areas of light showers
expected by Monday for areas along and west of the mountains.
Along with the cold weather, gusty winds will occur many of our
mountain and desert communities Monday through Wednesday. This
system will also bring the chance for light showers on Monday, and
heavier precipitation by later on Tuesday into Wednesday. This
cold system will bring lower snow levels and modest accumulating
snowfall to our mountain communities. The storm system will depart
Thursday, leading to drier weather and a slow warm up by the end
of the week.

&&

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

Update:

Plenty of sunshine again prevailed across Southern California
today. Highs across our service area ranged from 52 degrees at Big
Bear City to 81 at Palm Springs and Ocotillo Wells.

Cloudiness is on the increase this evening with marine layer
stratus moving into the inland valleys and to the coastal mountain
slopes. Spotty drizzle/light rain is possible late tonight
through Monday as the marine layer deepens. HRRR and WRF show
this and this is in the forecast, so no changes are needed this
evening.

Previous Discussion (Issued at 209 PM PST Sun Feb 20 2022):

We hope you folks west of the mountains enjoy those sunny skies we
have out there today because big changes are a comin'. A trough in
the Pacific Northwest continues its way south this afternoon with
California in its path. Significant pressure falls from the first
shortwave will occur later tonight, rapidly deepening the marine
layer and increasing west winds across the mountains and deserts.
This will lead to an increase in precipitable water values, where
some light showers along and west of the mountains will be
possible early Monday morning through Tuesday morning. WPC
guidance showing highest amounts will be focused on the coastal
slopes.

The main part of the show takes the stage by Tuesday afternoon as
a vorticity maxima surges southward along the Pacific coast,
digging out a stronger shortwave trough into Southern California.
This will bring in that cold Canadian air, where high temperatures
will be 5 to 15 (even 20 degrees!) below average by Tuesday and
Wednesday afternoons. Not only will it be cold, but those west
winds will continue to blow across the region. Coastal and valley
areas west of the mountains will see wind gusts 20-30 MPH, while
our friends in the mountains and deserts will see widespread
gusts near 50 MPH with 65-75 MPH readings possible along the
desert slopes. Please see the High Wind Watch for more details.

Precipitation will overspread the region by Tuesday afternoon,
becoming heaviest Tuesday night and Wednesday morning. Everyone
across the region should get in on the fun as WPC/NBM guidance
point to light amounts in parts of the deserts and the Inland
Empire and OC. Great totals will be across San Diego County, as
the east-west orientation of the trough depicts. Snow lovers, now
is your time to shine! Snow levels will start just over 4,000 feet
on Tuesday, lowering to locally near 2,500 feet by Wednesday. This
will produce some modest snow accumulations. Since it will be very
windy, this will create hazardous impacts for travel on mountain
roads, including along the 8 and the 15 through the mountains.
These conditions have led to issuance of the Winter Storm Watch
across the mountain areas Tuesday afternoon through Wednesday
evening.

Just as the storm has its fun rotating through SoCal, it will
quickly head on out by Thursday as a trough pushes south across
the West. We can expect a slow warming trend Thursday into next
weekend. This will also bring periods of offshore flow and dry
weather.

&&

.AVIATION...
210430Z...Coast and Valleys...BKN-OVC low clouds with bases 2500-
3500 feet MSL will continue to fill into the coastal basin tonight.
Coastal mountain slopes will be obscured in clouds/fog late tonight
through Monday morning. DZ/-SHRA possible along and west of the
mountains 12-20Z.

Elsewhere, SCT-BKN high clouds at/above 25,000 feet MSL through
Monday afternoon.

Southwest to west winds will continue to increase across the
mountain ridges, desert mountain slopes, and below the passes
tonight, with surface gusts 30-45 kts. Moderate to strong
up/downdrafts and LLWS likely over/east of the mountains.

&&

.MARINE...
No hazardous marine conditions are expected through Monday morning.
Strong west-northwest winds 20 knots or more and large, choppy seas
will begin to develop Monday afternoon. Winds strenghten Tuesday and
Wednesday with gusts 25 to 30 kts. A Small Craft Advisory will be in
effect from Monday afternoon to Wednesday evening. Winds will
diminish by Thursday morning. Periods of showers expected Tuesday
and Wednesday, along with a slight chance of thunderstorms Tuesday
night/early Wednesday morning.

&&

.BEACHES...
Short-period windswells from the northwest will bring elevated surf
at times Monday through Wednesday, mainly on west-facing beaches of
southern San Diego County. High rip current risk will accompany the
surf at all Orange and San Diego County beaches during this time.
Surf will peak at about 6 feet on Tuesday in southern San Diego
County.

&&

.HYDROLOGY...
Scattered, light rain showers will be possible beginning on Monday
and continuing into Tuesday along and west of the mountains. Any
accumulations will be spotty and light, except perhaps along the
coastal slope of the mountains where sustained upslope flow will
maintain saturation. Little to no significant runoff is expected.

For Tuesday evening into Wednesday, the showers will become more
widespread, and locally heavier, especially in thunderstorms,
which are possible. Rainfall in these heavier cells may contain
small hail as well. The snow level will drop to 3000 FT or lower
by Wednesday morning, limiting any significant runoff from higher
elevations. Any flooding issues will likely be brief and localized
in the heavier downpours. The larger rain totals are currently
focused over western San Diego County.

Preliminary precipitation totals from Monday through Wednesday are
as follows:
Deserts...0.05 to 0.25 inch Coastal and inland Orange
County...0.10 to 0.40 inch Inland empire...0.15 to 0.50 inch San
Diego County (coast/valleys)...0.50 to 1.00 inch Coastal mountain
slopes...1.00 to 1.50 inches (Mostly snow above 4000 FT).

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Watch from 7 AM PST Monday through late Tuesday night
     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 Watch from Tuesday afternoon through Wednesday
     evening for Riverside County Mountains-San Bernardino
     County Mountains-San Diego County Mountains.

PZ...Small Craft Advisory from 4 PM Monday to 10 PM PST Wednesday 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...Gregoria (Update)/APR (Previous Discussion)
AVIATION/MARINE...Connolly