Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 250509
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1009 PM PDT Thu Sep 24 2020

.SYNOPSIS...24/716 PM.

Locally gusty north winds along the Santa Barbara south coast and
Los Angeles and Ventura County mountains will diminish Friday
morning. Morning low clouds and fog will be confined near the
coast for Ventura and Los Angeles County. A significant warming
trend will begin on Sunday and continue through next week.

&&

.SHORT TERM (TDY-SAT)...24/1009 PM.

Clear skies remain in place across the area this evening, except
for a few patches of stratus southeast of Point Mugu. A strong
northwest low-level flow parallel to the California coast line
should develop an eddy circulation tonight. Stratus near the San
Diego and Orange County coastal areas should spread northward. Low
cloud coverage for the Los Angeles County coastal areas seems the
highest likelihood, but patchy low clouds and fog cannot be ruled
out along the Central Coast and into the Salinas Valley.

Onshore flow should strengthen some into Friday as a weak
shortwave trough will move over the region. 500 mb heights
continue to decline into Friday morning, then ridging aloft
should start to build in for Friday night.

Gusty northerly winds continue across southern Santa Barbara
County this evening. Winds gusts between 35 and 45 mph have been
recorded across the area early this evening. A wind advisory
remains in effect through early Friday morning for southern Santa
Barbara County. A marginal wind advisory remains in effect for the
Interstate 5 Corridor, but the start time was bumped back to
start at 11 pm tonight. Gusts to 41 mph are being recorded at
Warm Springs RAWS and wind are slated to increase some overnight
tonight.

An update was issued earlier to make tweaks to the wind advisory
and stratus.

***From Previous Discussion***

Very little change for Friday night and Saturday as heights
remain the same (592dm) and only a slight tilt to the northwest
flow aloft. There will continue to be northerly pressure gradients
with locally gusty north to northeast winds for the Santa Ynez
Range and the south Santa Barbara County coast, but below advisory
levels. It will remain breezy in the I-5 corridor again Friday
night. Areas of low clouds and fog for the south coastal area
looks good for Saturday morning.

By Sunday, a 595dm high pressure center builds northward off the
Oregon coast with our heights increasing 10dm and 950mb
temperatures bumping up 1-2 degrees C. Pressure gradients will be
trending weakly offshore which will also add some downslope
warming in the typical valleys and coasts of Ventura and Los
Angeles Counties. This will be the first day for a few valley
locations to reach 100 degrees or so. There will be some early
morning low clouds and fog for the south coasts on Sunday, but
this will be the start of rather long duration heat event which
will persist through the majority of next week.

.LONG TERM (SUN-WED)...24/139 PM.

Hot and dry conditions are likely to kick in over the entire
state on Monday as the high pressure center moves into Oregon and
the ridge extends down into Mexico. GEFS and ECMWF ensembles have
been consistent with indicating 700-500mb heights outside of
climatology for this time of the year on Monday. Heights will
approach 594dm which is not what we experienced in mid-August, but
rather unusual for late September. Pressure gradients will remain
weakly offshore and humidities will be low. The marine layer
should be about gone by Monday, so not expecting much coastal
stratus by then. High temperatures will be in the 95-105 degree
range for hotter valleys and the desert. Unfortunately the high
pressure ridge stalls out over the entire West Coast allowing the
heat to build through the week. For now, forecasts reflect the
hottest days on Tuesday and Wednesday with only minor relief later
in the week. Our local temperature forecasts are higher than the
majority of deterministic model data, but that is the correct
trend in this situation. There will be a few record-breaking
temperatures possible during this event, even though it`s not
expected to be as hot as the early Sept heat wave. No heat watches
are needed at this time, however, it`s very likely that heat
advisory levels will be reached in the valleys and possibly the
mountains on the hotter days. The other weather factor next week
will be the potential for large plume growth and rapid fire spread
with any new or existing fires due to the weak instability and
mixing heights above 10,000 ft each day.

&&

.AVIATION...25/0100Z.

At 22Z, the marine layer depth was around 700 feet deep at KLAX.
The top of the marine inversion was around 1500 feet with a
temperature near 24 degrees Celsius. There was another inversion
up to 2500 feet.

Moderate confidence in the current forecast for Los Angeles County
coastal terminals and terminals north of Point Conception. Higher
confidence elsewhere. There is a chance of LIFR to IFR conditions
for Los Angeles County coastal terminals and terminals north of
Point Conception between 10Z and 16Z.

KLAX...There is a 50 percent chance of LIFR to IFR conditions
between 10Z and 16Z. Any east winds will remain less than 7
knots.

KBUR...VFR conditions are expected at this time. No wind impacts
are expected.

&&

.MARINE...24/1008 PM.

Across the outer waters, Gale Force winds are expected at times
across much of the area through Friday night, especially during
the afternoon and evening hours. Large seas will affect the outer
waters through Saturday.

Across the inner waters north of Point Sal, SCA level winds will
continue tonight, possibly dropping below SCA levels late tonight
and early Friday morning, then increase again by Friday afternoon
and evening. Seas will remain above 10 feet through Saturday
morning.

Across the inner waters south of Point Conception, SCA level
winds are expected across western portions of the Santa Barbara
Channel through late tonight. Otherwise, SCA conditions are not
expected through Mon.

Patchy dense fog may affect the coastal waters tonight.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 9 AM PDT Saturday for
      zones 34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 3 AM PDT Friday for zones
      39-52. (See LAXNPWLOX).
     Wind Advisory in effect until 11 AM PDT Friday for zones
      53-54. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 9 AM PDT Saturday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Friday for zone
      650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Friday for zone
      670. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM Friday to 3 AM PDT Saturday
      for zone 670. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Saturday for zones
      673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Dangerously hot weather and near critical fire weather conditions
are possible all of next week as strong high pressure builds
across southwest California.

&&

$$

PUBLIC...Hall/EB
AVIATION...Hall
MARINE...Hall
SYNOPSIS...TF

weather.gov/losangeles


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