Area Forecast Discussion
Issued by NWS Los Angeles, CA

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679
FXUS66 KLOX 191116
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
316 AM PST Tue Nov 19 2019

.SYNOPSIS...19/153 AM.

A low pressure trough approaching the California Coast will
bring significantly cooler conditions today, and periods of rain
as well as mountain snow Wednesday and Thursday. Drier and warmer
conditions will return going into the weekend.

&&

.SHORT TERM (TDY-THU)...19/315 AM.

Srn CA is wedged between a trof that is entering the NW portion of
the state and a large upper low spinning about 500 miles to the
SSW of KLAX. Onshore trends have reduced the offshore flow to
about 1 MB both from the N and E. Marine layer stratus covers the
beaches of the Central Coast but is not making much inland
progress. There is a vort max (that no mdl has a clue about)
rotating around the upper low to the south that is spawning
numerous showers and TSTMs. It is about 130 miles south of San
Diego. Since it is embedded in the upper low`s circulation feel it
will soon begin to veer to the west and not affect the area still
it will be monitored. Otherwise mid and high level clouds will
impinge on Srn CA from both the south and the north resulting in a
partly cloudy morning and mostly cloudy afternoon. By late
afternoon a slight chc of light rain will develop over southern LA
county as a little PVA moves into Orange county and southern LA
county. Still the rain should hold off until the evening.

The weak offshore flow will switch to onshore flow later this
morning. Hgts will also fall by about 15 DM compared to ydy. These
two things along with the increased cloud cover will knock 10 to
20 degrees from yesterdays very warm highs. Highs today will come
in right around seasonal normals.

This evening the upper trof to the north will develop a cut off
low at its base. This upper low will be over Pt Conception at 12Z.
This low will bring increasing PVA LA and parts of VTA county this
evening and overnight and there will be an increasing chance of
showers through the period. As the cold core of the upper low
moves down through SLO and into SBA counties it will bring a chc
of instability showers to those areas after midnight.

The best chc for rain showers will be Wednesday as the upper low
swings through SBA VTA and then LA counties during the morning and
afternoon. SLO county and western SBA county will largely be left
out of this rain event. The best PVA and upper level divergence
will occur over LA county and the areas coast side of the mtns
will see the greatest amounts of rain. The core of the low has 500
mb temperatures of -24 degrees C, which will destabilize the
atmosphere as it rolls over the area. LI`s will drop to minus 2 to
minus 4. If convection does kick off CAPE values of 200 to 500
J/kg will support decent convection and a slight chance of
thunderstorms looks good.

Snow levels will drop to around 6,000 feet over Ventura and Los
Angeles Counties. Up to 6 inches of snow is possible for the Los
Angeles County mountains and about half that amount in the
Ventura County mountains. The eastern San Gabriel mountains will
see the highest amounts. A Winter Storm Advisory may be needed to
handle this snow.

Rainfall amount estimates call for less than a tenth of an inch
across SLO and most of SBA counties. Up to a quarter inch of rain
is possible for VTA county. The LA county coast from the coastal
slopes to the coast will likely8 recieve a quarter to a half inch
of rain. The eastern San Gabriel foothills will see the most rain
and nearly an inch of rain is possible.

It will be cool day for sure with 546 DM hgts, clouds and showers
all conspiring keep max temps down. Max temps across all of the
coasts and vlys will struggle to reach the mid 60s.

The upper low exits the area Wednesday evening and will leave
clearing skies and only a diminishing chc of a shower or two over
LA county.

Dry NW flow sets up Thursday behind the trof. Hgts will rise some
and skies will be partly cloudy at worst. temperatures will
remain below normal on Thursday under the trough and clouds. Max
temps will warm 2 to 4 degrees but will remain below normal.

.LONG TERM (FRI-MON)...19/206 AM.

The GFS and EC are not in good agreement at all for the extended
period. The GFS has a brand new solution for Friday with a cool
upper low moving into the area to the west of Pt Conception while
the EC has a weak ridge moving into the state. Have discounted the
abrupt change indicated by the GFS and used the EC soln which
calls for slightly warmer temps and mostly clear to partly cloudy
skies.

The mdl disagreement will not affect the weekend forecast that
much. Both mdls agree that the state will be under some sort of
cull area with week to moderate offshore flow. The offshore push
will keep the low clouds away, but skies will be mostly clear or
partly cloudy depending on if the cloudier GFS verifies or clearer
EC. The EC forecast warmer temps on Sat then cooler on Sun while
the GFS says the exact opposite. Took a blended approach to the
max temps for both days with max temps rising both days with the
biggest warm up on Saturday.

Bigger differences for the Monday forecast with the GFS
advertising a sharp inside slider while the EC keeps the state on
the backside of broad CONUS spanning trof. The ensembles favor the
EC and tilted the forecast in that direction with just slightly
cooler temps.

&&

.AVIATION...19/1050Z.

At 1030Z, there was a surface-based inversion at KLAX. The top
of the inversion was 2900 feet with a temperature of 23 degrees
Celsius.

Overall, moderate to high confidence in 12Z TAF package. At KSMX,
there is a 40% chance that no low clouds develop this morning and
there is a 40% chance of LIFR conditions at KSBP 12Z-17Z.
Otherwise, high confidence in TAFs through this evening. For
tonight, moderate confidence in timing of VCSH/SHRA development
south of Point Conception.

There is a slight chance of TSTMs this evening through Wednesday
morning across Ventura and Los Angeles counties.

KLAX...Overall, moderate confidence in 12Z TAF. High confidence in
VFR conditions through this evening. For tonight/Wednesday
morning, high confidence in development of -SHRA, but low
confidence in timing of -SHRA and associated MVFR CIGs. There is a
15% chance of a TSTM 10Z-18Z. Easterly wind component this morning
is expected to remain 5 knots or less.

KBUR...Overall, moderate confidence in 12Z TAF. High confidence in
VFR conditions through this evening. For tonight, high confidence
in development of -SHRA, but low confidence in timing and
associated CIG category.

&&

.MARINE...19/251 AM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds will develop today and continue
through Wednesday while seas increase to SCA levels tonight
through Wednesday night. There is a 30% chance of Gale force gusts
late this afternoon and tonight. For Thursday through Saturday,
winds and seas are expected to remain below SCA levels.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. High confidence in SCA level winds
and seas this afternoon through tonight. For Wednesday through
Saturday, winds are expected to remain below SCA levels with a 30%
chance of SCA level seas continuing through Wednesday.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. There is a 70% chance of SCA level
winds late this afternoon through tonight across the western half
of the Santa Barbara Channel. There is a 30% chance of SCA level
winds across the entire southern Inner Waters Wednesday afternoon
and evening. For Thursday through Saturday, high confidence in
winds and seas remaining below SCA levels.

There is a slight chance of thunderstorms south of Point
Conception tonight through Wednesday afternoon. Thunderstorms will
be capable of producing locally rough seas, brief heavy rain,
gusty/erratic winds and frequent lightning.

&&

.BEACHES...19/250 AM.

A cold storm system will move over the region between tonight
through Thursday. As this storm moves through, it will generate
high surf conditions along the coast from this evening through
Thursday morning. For the Central Coast, peak surf heights between
7 and 10 feet are expected while surf height of 4-8 feet are
expected south of Point Conception.

A HIGH SURF ADVISORY is in effect for the Central Coast as well as
the coasts of Ventura and Los Angeles counties from this evening
through Thursday morning. For west-facing beaches along southern
Santa Barbara County, a BEACH HAZARDS STATEMENT is in effect from
this evening through Thursday morning. Along with the high surf
conditions, strong and dangerous rip currents can be expected.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect from 6 PM this evening to noon
      PST Thursday for zones 34-35. (See LAXCFWLOX).
     Beach Hazards Statement in effect from this evening through
      Thursday morning for zone 39. (See LAXCFWLOX).
     High Surf Advisory in effect from 9 PM this evening to noon
      PST Thursday for zones 40-41-87. (See LAXCFWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PST Wednesday for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 6 PM this evening to 3 AM
      PST Wednesday for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST Thursday for
      zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 10 AM this morning to 3
      AM PST Thursday for zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

A cooler and showery weather pattern is expected Wednesday
through Friday. There is a slight chance of brief heavy downpours
in thunderstorms, especially Wednesday to Thursday morning. High
surf is possible at west-facing beaches late Wednesday through
early Thursday.

&&

$$

PUBLIC...Rorke
AVIATION...RAT
MARINE...RAT
BEACHES...RAT
SYNOPSIS...Smith

weather.gov/losangeles



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