Winter Storm in California, December 26, 2021

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
820 AM PST Sun Dec 26 2021

.SYNOPSIS...26/251 AM.

Periods of rain and mountain snow will prevail over the entire
area through Friday night. Temperatures will be significantly
below normal during the period.

&&

.SHORT TERM (TDY-TUE)...26/816 AM.

There were scattered clouds lingering over the mtns early this
morning, otherwise skies were mostly clear to start the day across
the region. Not much change can be expected thru this afternoon
with mostly sunny skies prevailing. Temps today will be well below
normal again, about 6-12 deg lower than seasonal norms. Highs
over the coast and vlys will only be in the 50s to near 60, except
40s across the Antelope Vly. Breezy W-NW winds should affect the
region today, altho should be quite gusty across the Antelope Vly
thru the afternoon.

A broad upper level trof with fast cyclonic flow aloft will
continue along the W coast at least through Tue, with a couple
more weather systems embedded in the upper level flow expected to
move into SW CA during the period. The first system, with a
vigorous cold front, will approach the area later tonight then
pass quickly thru the area Monday into early Mon evening, bringing
rain and mountain snow to all areas. Gusty SW-W winds will also
accompany the front, with strong and gusty winds possible in the
mtns as 850 mb winds increase to 40-50 knots. Rainfall amounts for
this system will likely range from a half inch to an inch for
most of the area. It will be another cold day on Mon with high
temps remaining in the 50s for the coast and vlys.

This will be a cold system with snow levels around 4000 feet.
There is a chance of slightly lower snow levels which would affect
the major mtn passes such as the Grapevine on Interstate 5. A
Winter Storm Watch is in effect for the SBA/VTA/LA mtns for most
of Mon into Mon night. There is the potential for 5 to 10 inches
of snow above about 4500 to 5000 feet along with wind gusts up to
55 mph. This would create hazardous wintry driving conditions with
snow covered roads, and very poor visibilities in snow and
blowing snow.

Min temps have to watched Tuesday night if skies clear out quick
enough there will likely be plenty of freezing temperatures in the
vlys and even in some interior coastal sections.

The second weather system will be a dry inside slider upper level
trof over eastern CA on Tue. A dry NW flow aloft will prevail over
the forecast area, with mostly sunny to partly cloudy skies overall.
Temps will fall about 5 degrees from Monday due to plenty of cold
air advection. Highs will only be lower to mid 50s for the coast and
vlys, except only in the lower 40s for the interior vlys. These
temps are about 15-20 degrees blo normal for late December, and
could be close to record low max temps for some areas.

.LONG TERM (WED-SAT)...26/349 AM.

The next storm will roll in on Wed and Thu. This will be a
different type of system than the ones during the previous 7 days.
Both the GFS and EC deterministic runs as well as their respective
ensembles show an impulse rotating out of Oregon early Wednesday
morning. This impulse carries enough energy to allow it to pinch
off into a low west of the Bay Area Wednesday afternoon. From
there the forecast gets tricky as there is no consensus on the
exact track of upper low. If the low tracks close to the coast
there will be a great deal of rain if it pulls to the west there
will be less (maybe much less) rain. Ensemble consensus favors a
solution somewhere in the middle. Will have to wait until the
event gets a little closer for a more accurate forecast. Good
confidence that max temps will remain in the 50s for much or the
area.

The wet pattern is forecast to break on Friday as dry northwest
flow sets up. Max temps will not change much.

A ridge is forecast to build over the area on New Years Day. There
will be light offshore flow. Looks for sunny skies but
unfortunately not much warmer.

&&

.AVIATION...26/1227Z.

At 12Z at KLAX, there was no marine layer nor an inversion.

Moderate to high confidence in TAFs. Timing of rain start at TAF
sites north of Point Conception could be off by +/- 2 hours. Vis
and cigs could drop to IFR conditions during periods of heavier
rain.

KLAX...High confidence in TAF. There is a slight chance conditions
will stay VFR thru period. There is a 30% chance that east wind
component will reach 10 kt, otherwise moderate confidence in east
wind component being 8 kt or less from 14Z-18Z.

KBUR...High confidence in TAF.

&&

.MARINE...26/550 AM.

In the outer waters, winds and seas are expected to drop below Small
Craft Advisory (SCA) levels by mid morning across the northern two
zones (PZZ670/673), but there is a chance that either winds or
seas could stay at SCA levels into this afternoon. Across the
southern zone (PZZ676), winds and seas are expected to continue
at SCA levels thru this evening. After a lull in the winds
tonight, SW winds are expected to increase late tonight, and will
probably reach SCA levels in most areas Mon morning. Winds will
shift to NW and increase Mon afternoon, possibly reaching Gale
force Mon afternoon thru late Mon night. SCA level winds will
likely continue in some areas Tue morning, then winds and seas
will be below SCA levels thru Wed. SCA level E winds are likely to
reach SCA levels Thu, especially across the southern two zones.

In the inner waters north of Pt Sal, seas are expected to drop
below SCA levels by mid morning. There is a 30% chance of SCA
level SW winds Mon morning, then there is a 50% chance of Gale
force NW winds Mon afternoon/evening. SCA level winds may continue
thru late Mon night. SCA conds are not expected Tue thru Thu.

In the SBA Channel and the inner waters S of Pt. Mugu, moderate
confidence that W-NW winds will drop below SCA levels by mid
morning. There is a 30% chance that SCA conds will linger into the
afternoon, especially across the inner waters S of Pt. Mugu.
There is a 50% chance of Gale force NW winds from mid afternoon
Mon thru late Mon night. SCA level winds may continue thru early
Tue morning, then SCA conds are not expected thru Wed night. There
is a 30% chance of SCA level E winds Thu.

&&

.BEACHES...26/552 AM.

Moderately large and long period northwest swell off the Central
Coast will generate high surf of 8 to 12 feet on exposed west and
northwest facing beaches of SLO County and western Santa Barbara
County. Surf is expected to subside during this afternoon.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 3 PM PST this afternoon
      for zones 34-35. (See LAXCFWLOX).
     Winter Storm Watch in effect from late tonight through late
      Monday night for zones 52>54. (See LAXWSWLOX).
     Wind Advisory in effect until noon PST today for zone 59.
     (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 AM PST this morning
      for zones 645-650-655-670-673. (See LAXMWWLOX).
     Gale Watch in effect from Monday afternoon through Monday
      evening for zone 645. (See LAXMWWLOX).
     Gale Watch in effect from Monday afternoon through late
      Monday night for zones 650-655-670-673-676. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PST this evening
      for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

An unsettled weather pattern will bring periods of rain and
mountain snow to the region through at least the middle of the
week. The rain will create slick roads and travel delays along
with moderate snow accumulations and wintry driving conditions in
the mountains.

&&

PUBLIC...Sirard/Rorke
AVIATION...Lund
MARINE...DB
BEACHES...DB
SYNOPSIS...TF

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