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000
FXUS66 KLOX 061154
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
354 AM PST Mon Dec 6 2021

.SYNOPSIS...06/307 AM.

A warmer than normal and continued dry day is forecast for today
as high pressure aloft remains in place. A weak weather system
will move over the region tonight through Tuesday and bring the
possibility of light rain. A stronger storm system will bring a
better chance of rain and mountain snow to the area between
Wednesday night and Thursday, tapering off to showers Thursday
night. A cool air mass is expected to linger into the weekend.

&&

.SHORT TERM (TDY-WED)...06/352 AM.

Offshore flow, weaker for the southern areas, remains in place
this morning beneath weak ridging aloft. The flow pattern appears
to not be strong enough to unseat the persistent marine layer
depth remaining at coast. Very patchy low clouds and dense fog are
dancing around the coastal and lower valley areas this morning,
forming in place then dissipating. Temperatures should be above
normal for today across the region with exception to the coastal
areas where a more maritime air mass could remain wedged in.
Winds should be trending downward and no wind advisories are
expected for this morning. Locally gusty offshore winds could
remain this morning, especially through and below passes and
canyons.

The flow regime will transition rather quickly today from
offshore to onshore. High clouds are already streaming over the
region this morning ahead of a weak weather system located near
40N and 150W. This trough will drop into the region late tonight
and into Tuesday. If high-resolution models and the NAM BUFR time
heights play out, a surge of low clouds and fog will move in with
the sea breeze later today. The forecast does not go that
aggressive but trends that direction with an early evening arrival
across most coastal locales. Deterministic NAM-WRF and GFS
surface pressure gradients have greater than a 5 mb reversal
today, switching from weak offshore flow this morning to moderate
onshore flow by late this afternoon.

Clouds will increase through tonight. Rain should spread into the
northern areas overnight or early Tuesday morning, then spread
south into Tuesday. NAEFS ensemble suggests mixing ratios and
precipitable waters values around 4 standard deviations above the
mean. GEFS, CMC, and EPS ensemble members agree that precipitable
waters increase to between 1.1 and 1.3 inches for KVBG, or about
200 percent of normal for this time of year. NAM-WRF 850 mb mixing
ratios increase to between 8-9 g/kg. What this all means is that
PoPs have been increased for areas north of Point Conception and
for southern and eastern Los Angeles County between tonight and
Tuesday. Most of the Ventura County coast and valleys, the Santa
Clarita Valley, and portions of the Santa Barbara South Coast and
the San Fernando valley will likely be in the rain shadow of the
Transverse Mountain range and PoPs remain on the drier side as
there is a lesser chance of measurable rain due to the low-level
northwesterly flow. Rainfall amounts will be light at best,
ranging from zero to around a tenth of an inch. Snow levels will
be quite high with this system and no accumulating snow is
expected.

Shortwave ridging aloft will build in between Tuesday night and
Wednesday. Outside of today, Wednesday could the warmest day of
the remainder of the work week. Onshore flow does remains in
place and some semblance of marine layer induced low clouds and
fog could linger. High clouds ahead of the next system will
likely keep mostly clear to partly cloudy skies in place, but EPS
and GEFS ensemble members favor less clouds during this period.

.LONG TERM (THU-SUN)...06/349 AM.

To be updated soon.

&&

.AVIATION...06/0608Z.

At 0501Z at KLAX, the marine layer was 600 feet deep. The top of
the inversion was around 2700 feet at a temperature around 22 C.

High confidence in KPMD, KWJF, KBUR, and KVNY TAFs. Moderate
confidence in remaining TAFs. There is a 30% chance of IFR/LIFR
conditions at LA and Ventura County coastal sites 09Z-17Z. Low
clouds may arrive at KPRB between 10Z-12Z with a 30% chance of
remaining VFR.

KLAX...Moderate confidence in TAF. There is a 30% chance of 3SM BR
OVC005 09Z-17Z. High confidence that any significant east wind
component will remain 5 kt or less.

KBUR...High confidence in TAF.

&&

.MARINE...06/154 AM.

High confidence that SCA level NW winds will continue through
late tonight across the outer waters along the Central Coast to
San Nicolas Island. There is a 30% chance of Gale force gusts at
times, especially during the afternoon and evening. For the
nearshore waters along the Central Coast, some short period seas
will move into the waters but only expecting localized SCA
conditions.

For Tuesday and Wednesday, conditions will be fairly quiet. NW
winds will strengthen across all the waters on Thursday and a
large northwest swell will also start to build. High confidence in
widespread SCA level winds across all the waters for Thursday,
likely extending through Friday as well. For the outer waters,
moderate confidence in Gale force winds. Hazardous seas of at
least 10 feet are also likely across the outer waters.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PST Tuesday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

A storm system will bring rain and mountain snow to the region
between late Wednesday night and early Friday. Gusty northwest to
north winds are forecast to develop between Thursday night and
Friday. Gales are possible across the coastal waters between
Thursday and Friday.

&&

$$

PUBLIC...Hall
AVIATION...Stewart
MARINE...Stewart
SYNOPSIS...Hall

weather.gov/losangeles