Avalanche in California, March 1, 2023

Area Forecast Discussion
National Weather Service San Diego CA
412 AM PST Wed Mar 1 2023

.SYNOPSIS...
A cold Pacific storm will move through the area today with heavy
precipitation this morning and showers with much lower snow levels
for this afternoon. Strong gusty west winds will diminish tonight.
Dry with gradually warmer days for Thursday and Friday. For the
weekend into next week, a low pressure system near the Pacific
Northwest coast will bring stronger onshore flow with slightly
cooler days and stronger and gusty west winds for the mountains
and deserts. Most precipitation is expected to stay to the north.

&&

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

.SHORT TERM (Today through Friday)...
The center of a cold low pressure system is moving southward
through the central valley early this morning. Warm advection
precipitation has been occurring overnight with the greatest
rainfall at lower elevations of 1 to 1.5 inch in portions of the
Inland Empire toward the coastal slopes of the mountains.

Snow levels will rise to 4500 to 5000 feet early this morning,
then fall to 1500 to 2000 feet by early evening. Widespread rain
and mountain snow will become more showery by afternoon with
showers decreasing from the northwest during the afternoon and
ending during this evening.

Rainfall and liquid equivalent above the snow level from Tuesday
evening through this evening will range from one-third to one-
half inch near the coast to 2 to 3 inches in the mountains with
local amounts to around 4 inches. Amounts in the deserts will
range from around one-tenth inch to around one-half inch near the
foothills of the mountains. The San Diego River at Fashion Valley
is forecast to rise to 9.4 feet which could flood low water
crossings from late this morning through this evening.

In the mountains, snowfall of 1 to 2 feet is expected above 5000
feet with snowfall locally exceeding 3 feet on the higher peaks in
the San Bernardino Mountains. Most areas above 4000 feet will have
at least 3 inches of new snowfall. If showers linger long enough
in the valleys for snow levels to fall sufficiently, there could
be some snow showers in the far inland valleys near the coastal
slopes of the mountains for this afternoon and early evening. A
Winter Weather Advisory has been issued for those areas to account
for that possibility.

There were a few lightning strikes earlier in the night near the
Santa Barbara County coast so a slight chance of thunderstorms has
been added to the forecast for today as the coldest mid level air
moves across the area.

Southwest to west winds will strengthen this morning and become
west to northwest in the afternoon. The winds will become more
northerly and diminish tonight. High temperatures will be well
below average today, as much as 20 to 25 degrees above average for
some inland areas. Tonight will be a cold night with frost or
freeze conditions for much of the coast and valleys. Lows for
those areas will be mostly in the 30s and into the 20s in the
more wind-sheltered inland valleys. Overnight temperatures will
then slowly moderate into the weekend.

Thursday will be dry and several degrees warmer. The warming will
continue on Friday, but with high temperatures still mostly 5 to
10 degrees below average.

&&

.LONG TERM (Saturday through Tuesday)...
A low pressure system centered near the Pacific Northwest coast
will bring stronger onshore flow for southern California. High
temperatures will be a few degrees cooler for the weekend into
next week with periods of gusty west winds in the mountains and
deserts. Most precipitation is expected to remain to the north
with a less than 10 percent chance for some light measurable
precipitation amounts, mostly in the mountains. Temperatures will
likely remain well below average through much of next week.

&&

.AVIATION...
011030Z...Clouds with variable bases 1500-4000 feet MSL and
additional layers up to 10000 feet. RA and mountain SN through 20Z
with mountains mostly obscured. RA/SHRA tapering off from northwest
to southeast after 20Z, ending by 05Z. CIGS locally lowering to 1200-
2500 feet MSL with vis 2-4SM in showers. Isolated CIGS down to 800
feet with vis 1SM in heavier SHRA. Rapid clearing north to south
overnight into Thursday.

Southwest to west winds sfc gusts 25-35 kt at the coast and valleys,
and 30-45 kt in the mountains and deserts with isolated gusts to 60
kt on the desert slopes. STG-SVR up/downdrafts, LLWS, and rotors
likely over and NE/E of the mountains. Rotors likely VCTY KPSP at
times. Winds weakening for the coastal areas and valleys evening.

&&

.MARINE...
Hazardous winds and seas today and most of tonight. West winds are
expected to gust 35 to 40 kt with seas of 10 to 14 feet. Strongest
winds are expected from 6 AM through 10 PM, then lowering into
Thursday morning. Check the Gale Warning for more details.
Conditions will improve rapidly Thursday morning and no additional
marine hazards are expected through Sunday.

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory until 6 PM PST this evening for Orange County
     Coastal Areas-Orange County Inland Areas-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Valleys.

     Winter Weather Advisory from 1 PM this afternoon to 6 PM PST
     this evening for San Bernardino and Riverside County
     Valleys-The Inland Empire.

     Winter Weather Advisory from 3 PM this afternoon to 8 PM PST
     this evening for San Diego County Valleys.

     Winter Storm Warning until 4 PM PST this afternoon for San
     Bernardino County Mountains.

     Winter Storm Warning until 10 PM PST this evening for Riverside
     County Mountains-San Diego County Mountains.

     Winter Weather Advisory until 6 PM PST this evening for Santa
     Ana Mountains and Foothills.

     Winter Weather Advisory until 4 PM PST this afternoon for Apple
     and Lucerne Valleys.

     High Wind Warning until 10 PM PST this evening for Coachella
     Valley.

     High Wind Warning until 10 PM PST this evening for San Diego
     County Deserts-San Gorgonio Pass Near Banning.

PZ...Gale Warning until 4 AM PST Thursday 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...17
AVIATION/MARINE...MM