NWS San Diego, CA wrote its last area forecast discussion before the first event at Dec 10, 9:28 PM PST, 2 hours 32 minutes earlier.
Area forecast discussion, Dec 10, 9:28 PM PST, 2 hours 32 minutes before
Area Forecast Discussion
National Weather Service San Diego CA
928 PM PST Sat Dec 10 2022
.SYNOPSIS...
A winter storm system will push south into California, bringing
widespread rain and mountain snow to the area. The storm will spread
rain and high elevation snow from north to south across Southern
California beginning early Sunday morning. Steadier rainfall and
strong southwest winds will accompany the cold front on Sunday,
becoming more showery and colder on Monday, with snow levels
lowering over the mountains. Periods of locally heavy rainfall will
be possible, especially Sunday morning into Sunday afternoon. There
is a small chance of thunderstorms Sunday night into Monday morning.
The storm will exit to the east Monday night, but colder than normal
weather will continue through midweek. Another weather system will
take shape off the coast after midweek, with the potential to bring
more precipitation towards the end of next week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Evening Update:
At 9 PM, satellite imagery showed thickening clouds moving into
SoCal ahead of the major winter storm system now affecting Central
California. Very light rain was also beginning to move into the LA
Basin from the west. No major changes were needed this evening. We
are still expecting to see widespread rain close to daybreak Sunday
from the northwestern portion of the area, including Orange and San
Bernardino Counties, spreading southeast Sunday morning. Heavy rain
and winds is expected to accompany the frontal boundary moving
through from late morning through afternoon.
Remainder of the Saturday afternoon discussion:
A storm system currently situated off the coast of the Pacific
Northwest will rapidly advance southward today, pushing into
Northern California tonight. A cold front trailing the storm system
will begin to impact Southern California early Sunday morning,
bringing widespread rain and mountain snow. The highest rainfall
rates, possibly in excess of 1/2 inch per hour, are expected to
occur Sunday morning into Sunday afternoon with the cold front
passage. Snow levels will initially be quite high Sunday morning,
hovering around 6,500 to 7,000 feet, then rapidly dropping to around
3,500 to 4,500 feet Sunday night once the cold front passes.
After the cold front passage, rain will become less widespread and
heavy, with only scattered rain showers expected Sunday evening. As
the storm system continues to progress south, another wave of rain
and mountain snow will occur late Sunday night into Monday
afternoon. Very cold air aloft will be pulled into SoCal by this
wave, which will destabilize the atmosphere, bringing a small chance
of thunderstorms late Sunday night into Monday morning. Showers will
end from north to south Monday evening through Monday night, with
Tuesday expected to be a mostly dry day.
Here are the forecast rainfall totals Sunday and Monday:
Coast and Valleys: 1 to 1.5 inches
San Bernardino Mountains: 2.5 to 4.5 inches
Riverside and San Diego Mountains: 1.5 to 3 inches
Deserts: 0.15 to 0.40 inch
The highest snowfall totals will be confined to elevations above
6,500 feet, with 6 to 10 inches of snowfall expected between 6,500
and 7,000 feet. Above 7,000 feet, snow totals could reach 12 to 20
inches. From 4,500 to 6,500 feet, expect snow totals of 2 to 6
inches. A Winter Storm Warning has been posted for the mountains
above 4,500 feet.
In addition to the rain and snow, strong and gusty southwest winds
will occur over the desert slopes of the mountains Sunday, with peak
wind gusts of 55 to 65 mph. Some gusts could reach 70 mph on the
desert slopes of the San Bernardino Mountains. There will be breezy
winds at the coast and in the valleys as well, with gusts 25 to 35
mph possible. In the wake of this storm system, very cold air will
be left behind. High temperatures on Monday and Tuesday will be 10
to 20 degrees below normal, with cold overnight lows as well.
As this system pushes east, a cutoff low pressure system looks to
take shape near the Northern California coast mid next week. Since
this storm is cut off from the mean atmospheric flow, it is highly
unpredictable, especially this far out. Current ensembles and
guidance have it hanging off the California coast for a day or two
mid next week, then pushing into California sometime towards the end
of the week. The ensemble QPF spread remains quite large late next
week, so lots of uncertainty at this time. For now, the forecast has
increasing chances of precipitation beginning Thursday night and
increasing throughout the day Friday.
&&
.AVIATION...
110435Z...Coast/Valleys...SCT-BKN with bases 1500-2500 FT MSL are
beginning to fill in across the coast and valleys, and will become
more widespread overnight. -SHRA will be possible after 08z Sun,
with more widespread and heavier RA after 14z Sun in Orange/SBD
County, reaching Riverside/San Diego County after 17z Sun. Lower
bases of 1000-1500 FT MSL and reduced vis in +RA, mainly 18z-22z
Sun. Increasing S-SW winds after 08z Sun in Orange County and after
12z Sun in San Diego County, with gusts of 25-35 kt, local gusts to
40 kt, including vcty KSAN/KCRQ/KSNA. Winds will turn westerly with
gusts 20-30 kts and continued SCT SHRA for Sun afternoon/night.
Mountains...Increasing clouds tonight. -SHRA/-SHSN developing across
SBD mtns after 08z Sun, with heavier precip after 15z Sun, and
southern mtns after 19z Sun. Snow levels starting at 6,000-7,000 FT
MSL, before lowering through the day to 3,500-4,000 FT MSL Sun
night. Strong S-SW winds through Sun, highest Sun morning for SBD
Mtns with gusts of 40-55 kt, local gusts to 70 kt. Increasing winds
for Orange/Riverside/San Diego Mtns after 14z Sun, with peak gusts
of 35-50 kt. Expect STG-SVR UDDFS for all mtns. Winds will continue
to gust 30-40 kts through Sun night.
Deserts...SCT high clouds through Sun. Increasing S-SW winds across
SBD County with surface gusts 35-45 kt, peaking Sun morning. Winds
will turn to the W Sun afternoon, with gusts 30-40 kt. Increasing
mid-level clouds are expected Sun morning, with SHRA possible VCTY
KVCV and KPSP after 16z Sun.
&&
.MARINE...
No hazardous marine conditions are expected through late this
evening. Gusty southwest winds will develop very early Sunday
morning and turn to the northwest early Sunday afternoon, with peak
wind gusts of 25-32 knots expected. Rough seas, strong winds and
heavy rain leading to reduced visibility will occur through much of
Sunday and Monday. A slight chance of thunderstorms is expected over
the coastal waters starting late Sunday into Monday morning.
Conditions will improve on Tuesday.
&&
.BEACHES...
A longer-period WNW swell of 7-10 feet at 12-14 second periods will
arrive at the beaches after 12z Sun. This may lead to some wave sets
of up to 6 feet on some of the west-facing beaches in Orange and San
Diego Counties on Monday and Tuesday, as well as enhanced risks for
rip currents.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 4 AM to 6 PM PST Sunday 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-Santa Ana Mountains
and Foothills.
Flood Watch from late tonight through Sunday afternoon for
Riverside County Mountains-San Bernardino County Mountains.
Winter Storm Warning from 6 AM Sunday to 10 PM PST Monday for
Riverside County Mountains-San Bernardino County Mountains.
Winter Storm Warning from 6 PM Sunday to 10 PM PST Monday for
San Diego County Mountains.
Wind Advisory from 4 AM Sunday to 4 AM PST Monday for Apple and
Lucerne Valleys.
Wind Advisory from 4 AM Sunday to 8 AM PST Monday for Coachella
Valley-San Diego County Deserts-San Gorgonio Pass Near
Banning.
PZ...Small Craft Advisory from 1 AM Sunday to 4 PM PST Monday 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...Connolly/JMB
AVIATION/MARINE/BEACHES...Schenk