Flash Flood Warning 7, NWS Los Angeles, CA

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
435 PM PST Mon Jan 9 2023

.SYNOPSIS...09/119 PM.

A strong Pacific storm system will affect the entire area through
Tuesday. There will be periods of heavy rain, strong winds,
flooding and chance of strong thunderstorms. It will be dry
Wednesday through Friday. Another storm will move across the area
over the weekend.

&&

.SHORT TERM (TDY-THU)...09/206 PM.

A potent storm with significant AR tap continues to drop
heavy rain and isolated thunderstorms west of LA County this
afternoon. The heavy rain and storms have been expanding east and
will spread through LA County this afternoon and evening. Along
with the AR tap the system has a strong low level southerly jet
and ample dynamics aloft to maximize rainfall efficiency, leading
to significant rates and totals, especially in upslope areas. As
an example, San Marcos Pass is already over 10 inches for the
storm while coastal areas of southern Santa Barbara County are at
3-5 inches. SLO County rainfall has been a bit less but still
impressive at 4-7" in the coastal mountains and 2-3 along the
coast. Meanwhile in LA County amounts range from 1-2 inches along
the LA/Ventura County line to just a quarter inch or less near
the Orange County/San Bernardino County line.

Santa Barbara County and portions of Ventura County will remain
under the gun through early evening with periods of very heavy
rain. This will shift east into LA County during the evening and
overnight hours with rain rates west of LA County tapering off to
a quarter inch or less after around 10pm.

Snow levels through this evening will be over 8000' so minimal
snow impacts locally for this first phase of the storm.

The second part of the system, expected to arrive late tonight for
SLO County and Tuesday morning to the south will be more
convective with models indicating CAPE values between 500-1000
J/kg. Ample lightning has been continuously detected with that
area and the expectation is that it will mostly hold together as
it moves into the area. High res models currently are not showing
rain rates exceeding one inch per hour as PW's drop from over an
inch today to around a half inch Tuesday, but given the
convective nature all areas will be susceptible to periods of heavy
showers and storms.

Snow levels will be lowering as this next phase is colder and more
unstable. Could see a few inches of snow down to around 6000' on
Tuesday.

Shower coverage expected to decrease in aerial coverage and
intensity during by afternoon with dry conditions by Tuesday
night.

Wed and Thu expected to be dry with warming temps, except chilly
in the morning with lows in the 30s and 40s across coast and
valleys.

.LONG TERM (FRI-MON)...09/222 PM.

Looks like at least one more dry day Friday before the next system
arrives over the weekend. There is still a fair amount of
uncertainty on the timing, however virtually all the ensemble
members show rain returning to all areas by at least Saturday
night. The GFS has an initial impulse coming through Saturday
morning followed by the main frontal band Saturday night into
Sunday morning. The ECMWF shows a similar pattern and both
indicate amounts in the half to one inch range. However, there are
more than a few ensemble members that show amounts over an inch
and a couple over 2". So still some uncertainty with timing and
amounts but high confidence that rain will return area-wide.

Snow levels are expected to be lower with this system, but still
not quite sure how low as there is quite a large spread in the
various ensemble solutions with regard to how much cold air will
drop into the area. Good chance snow levels will drop to at least
6000' with a possibility of accumulations at lower levels.

Some models showing a weaker follow up system late Sunday into
Monday but will see how that evolves over the coming days.

&&

.AVIATION...10/0034Z.

At 2234Z, there was no marine inversion or marine layer at KLAX.

Overall, low to moderate confidence in 00Z TAF package. High
confidence in rain through the TAF period, but low to moderate
confidence in flight categories and timing of category changes.
Isolated tstm activity was noted near KCMA / KOXR associated with
some of the heavier rain bands moving into Ventura County. Also,
unstable air will move into the area late this evening and Tuesday
morning, resulting in the potential for TSTMs and VCTS remarks
have been included for all sites.

KLAX...Low confidence in 00Z TAF. High confidence in CIG/VSBY
restrictions with rain, but low confidence in timing of flight
category changes between MVFR and IFR conditions. There is a
40-50% chance of east to southeast winds around 10-15 kt through
the afternoon, which may persist into the evening, and again
06z-18z Tue.

KBUR...Low confidence in 00Z TAF. High confidence in CIG/VSBY
restrictions with rain, but low confidence in timing of flight
category changes between MVFR and IFR.

&&

.MARINE...09/229 PM.

For the Outer Waters, moderate to high confidence in current
forecast. The GALE WARNING has been dropped in zone 670. Winds
will continue at Small Craft Advisory (SCA) levels with SCA level
winds continuing through Tuesday night, although there is a 30
percent chance of another burst of GALE FORCE gusts Monday
morning. For zones 673/676, the GALE WARNING will continue until
05z, before subsiding to SCA levels and persisting into Tuesday
afternoon. For Wednesday through Friday, there is a 40-60% chance
of SCA level winds (especially across PZZ670/673). As for seas,
SCA level waves will continue through Friday with seas of 10-16
feet.

For the Inner Waters north of Point Sal, moderate confidence in
current forecast. The GALE WARNING has been dropped. Winds have
diminished to Small Craft Advisory (SCA) levels with SCA level
winds continuing through Tuesday evening. For Wednesday through
Friday, winds are expected to remain below SCA levels. As for
seas, high confidence in SCA level seas through Wednesday, then
moderate confidence in widespread SCA level seas for Thursday and
Friday.

For the Inner Waters south of Point Conception, moderate
confidence in current forecast. Today through Tuesday evening,
high confidence in SCA level winds for all the southern waters.
For the western half of the Santa Barbara Channel, the GALE
WARNING remains in effect through 05z. For Wednesday through
Friday, high confidence in winds remaining below SCA levels with a
40% chance of SCA level seas.

For all the coastal waters, there is a threat of thunderstorms
developing tonight and Tuesday. Any thunderstorms that develop
will be capable of producing gusty outflow winds, rough seas,
heavy rainfall, dangerous cloud to surface lightning, and possible
waterspouts.

&&

.BEACHES...09/1028 AM.

The HIGH SURF ADVISORY for both the Central Coast and the Ventura
Coast through Tuesday looks on track. However, will likely need
to extend this as high surf should continue into the weekend. Los
Angeles County beaches and Santa Barbara county south coast will
continue to see elevated surf of 3 to 6 feet with strong rip
currents today, resulting in the Beach Hazards Statement. It will
be necessary to expand the high surf advisory to the south coast
of Santa Barbara County and coast of Los Angeles County beginning
Tuesday. changes will be introduced this afternoon.

The train of strong storms continues on Tuesday at least and HIGH
SURF ADVISORIES will be likely (60-70 percent chance) for the
entire coastline into next weekend. As a matter of fact, the
highest waves will impact west and northwest facing beaches from
Wednesday through next Saturday.

For more details about the High Surf Advisories, please refer to
the Coastal Flood Advisory product (LAXCFWLOX). Stay tuned to
National Weather Service forecasts during this very active
situation.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Warning in effect until 4 PM PST Tuesday for zones
      53-353. (See LAXNPWLOX).
     Flood Watch in effect through Tuesday afternoon for zones
      53-354>359. (See LAXFFALOX).
     High Wind Warning in effect until 7 PM PST Tuesday for zones
      54-59. (See LAXNPWLOX).
     Flood Watch in effect through Tuesday evening for zones
      54-59-88-362>365-547-548. (See LAXFFALOX).
     Wind Advisory in effect until 10 PM PST this evening for
      zones 87-88-340>352-354>359-362>365-547-548. (See LAXNPWLOX).
     Beach Hazards Statement in effect through late tonight for
      zones 87-349-350-362-364. (See LAXCFWLOX).
     High Surf Advisory in effect from 6 AM to 10 PM PST Tuesday
      for zones 87-349-350-362-364. (See LAXCFWLOX).
     High Surf Advisory in effect until 10 PM PST Tuesday for
      zones 340-346-354. (See LAXCFWLOX).
     Flood Watch in effect through Tuesday morning for zones
      340>353. (See LAXFFALOX).
PZ...Gale Warning in effect until 9 PM PST this evening for zones
      645-670-673-676. (See LAXMWWLOX).
     Gale Warning in effect until 6 PM PST this evening for zone
      650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 7 PM PST Tuesday for
      zone 655. (See LAXMWWLOX).

&&

PUBLIC...MW
AVIATION...Phillips/Sweet
MARINE...Sweet/RAT
BEACHES...Sweet/RAT
SYNOPSIS...MW/Rorke

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox

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