Gale Warning 5, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
911 PM PST Mon Feb 27 2023

.SYNOPSIS...
Low pressure aloft will bring occasional rounds of rain and mountain
snow through Tuesday, becoming heavier and more widespread Tuesday
night and Wednesday. Gusty southwest to west winds will occur over
the mountains and deserts, becoming strong and potentially damaging
on Wednesday. The strong winds will spread to the coast and the
coastal waters on Wednesday as well. Fair weather will return
Thursday and continue through the weekend.

&&

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

Radar has indicated scattered, light showers all evening drifting
east and southeast across the CWA. Rainfall has been less than 1/4
inch, with many sites, less than 1/10 inch in the lower elevations
through 8 PM PST. As this wave of showers weakens, more will follow
overnight, with notable breaks in between, if the high resolution
models are right. Snow is falling above 4000 feet north, and 4500
feet south. These levels will slowly fall overnight. a strong sfc
pressure gradient to the high deserts is supporting some wind gusts
already this evening over 50 MPH in the northern mountains. Our 00Z
Miramar sounding had a deep moist layer, topped by a weak inversion
near 8000 FT MSL. The precipitable water is about 1/2 inch. No Zone
Forecast updates are planned this evening. A number of Advisories
and Warnings are now in effect, and another Wind Advisory will be
needed for coastal areas on Wednesday, when west wind gusts to
around 45 MPH look likely if the cold, digging trough remains on
track.

From previous discussion...

Snowfall will be variable due to the showery nature of the precip in
the mountains, but will generally be 3-6 inches in the San
Bernardino County Mountains through Tuesday, which will add to the
issues with previous snow/snow removal/road closures there.

The main wave with the broad West Coast trough will move through
southern Nevada Wednesday, and with strong west flow over SoCal and
a weak atmospheric river, there will be more precipitation, locally
heavy. This will be a cold storm, though some brief warming could
occur Tuesday night with the atmospheric river. Snow levels of 4000-
4500 feet initially should fall to around 2500 feet north of San
Diego County by Wednesday afternoon, with NBM 1-D viewer showing the
snow level possibly down to 1500 feet around SBD when some light
lingering precip occurs late Wednesday afternoon. Total snowfall
Tuesday night-Wednesday of one to two feet will be possible in parts
of the mountains, especially west and southwest slopes, though San
Diego County will be mostly below one foot. Winds will add to the
winter storm threat with gusts to 80 MPH possible from the crests
into the desert slopes, and blowing and drifting of snow will occur.
High-resolution models indicate rainfall rates locally over 1/3 inch
per hour along somewhat convective bands, but that should remain
below flash flood guidance, and the thunderstorm chance is rather
small, less than 15% during any 6 hourly period and CAPE values
mostly 250 J/kg or less, even over the warmer surface of the coastal
waters. General total precip through Wednesday evening will be
around 1/2" near the coast, 1/2" to 1" in the valleys, with local 2-
4" of liquid on the coastal mountain slopes.

After the main trough moves east, warmer weather with weak offshore
flow to the north will occur Thursday, though temperatures remain
below normal through next weekend. Waves will continue to move east
across the Pacific west of the Pac NW/Canada to maintain the
longwave trough over really much of North America. Cluster analysis
shows some hint of at least zonal flow or even slight ridging over
SoCal and the southern part of the western US early next week, about
a 35% chance of the GEFS/EPS/Canadian ensembles, but the other
solutions keep the West Coast trough pattern which would likely
bring another round of precipitation sometime early next week. There
is a rather large range of potential high temperatures then from
basically the 50s to perhaps just beyond 70 in near-coastal areas.

&&

.AVIATION...
280500Z...SCT-BKN clouds with bases 2500-4000 ft MSL and layers up
to 7500 ft MSL continuing through about 15Z Tue, with bases
generally above 3000 ft MSL afterwards. Coastal slopes remaining
obscured through Tuesday evening. Current band of showers moving
east dissipating by 10Z. A second band of showers moves in Orange
County/far west San Bernardino County by 09Z, spreading south and
east through about 18-20Z. Bases locally lowering to 1500 ft MSL
with 2-4 SM vis in showers this evening and Tuesday morning.
Isolated CIGS down to 800 ft MSL with 1 SM vis in heaviest showers.

Southwest to west winds will increase over the mountains and deserts
this evening with sfc gusts 30-40 kts with isolated gusts to 50 kts
along the wind prone desert slopes, weakening after 14Z Tue, then
increasing again Tuesday evening with gusts 30-50 kt again. STG
up/downdrafts, LLWS, and rotors likely over and NE/E of the
mountains. Rotors likely VCTY KPSP at times.

&&

.MARINE...
Winds will strengthen and seas will build late Tuesday, leading to
hazardous boating conditions Tuesday night through Wednesday night.
West to northwest gales 25 to 30 kt with gusts to 35 kt are expected
Tuesday afternoon and continue through Wednesday. Local gusts to 40
kt possible with convective showers Wednesday afternoon and evening.
Conditions improve on Thursday as winds and seas lower.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Storm Warning until 4 PM PST Wednesday for San Bernardino
     County Mountains.

     Winter Storm Warning from 6 PM this evening to 10 PM PST
     Wednesday for Riverside County Mountains-San Diego County
     Mountains.

     High Wind Warning from 2 PM Tuesday to 10 PM PST Wednesday for
     Apple and Lucerne Valleys-San Diego County Deserts-San
     Gorgonio Pass Near Banning.

     High Wind Warning from 6 AM to 10 PM PST Wednesday for Coachella
     Valley.

PZ...Gale Watch from Tuesday afternoon through Wednesday evening 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...10/Maxwell
AVIATION/MARINE...SS