907
FXUS66 KLOX 200055 AAA
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
555 PM PDT Wed Jun 19 2024

.SYNOPSIS...19/1254 PM.

Onshore flow will maintain near-normal temperatures across the
region through Thursday with overnight low clouds and fog along
the coast and valley areas. Expect warming beginning on Friday
with above normal temperatures, especially in the interior where
dangerously hot weather is possible over the weekend.

&&

.SHORT TERM (TDY-SAT)...19/136 PM.

Synoptically, the area is under an upper-level trough that extends
over the western two thirds of the CONUS. By late Friday this
feature will have moved to the east and the area will be in a
broad area of higher pressure. By Sunday the peak of the high will
be located near the four-corners area, a position favorable to
transport moisture to the area during the monsoon season, and
models are indicating there is over one inch of perceptible water
heading our way with it. This will complicate the temperature
forecast and could possibly lead to some afternoon mountain
showers although they are not currently indicated. Higher heights
will remain in place throughout the week until another trough
drops down the California coast on Friday.

Temperatures are currently 2-4 degrees cooler along the coast
with stronger onshore flow along the south coast and some
lingering marine clouds. Heights are also a bit lower today. Onshore
flow ad the LAX-DAG gradient is up to 5.3 and this may keep some
south coast beaches cloudy all afternoon. Still expecting strong
NW winds coming off the waters of the Central Coast to filter
through the Western Santa Ynez range and produce low end advisory
level gusts across the western half of the SBA south coast this
afternoon and evening.

Two competing forces will be at work on the marine layer cloud
pattern on Thursday as increasing troffing aloft combines with the
eddy to promote cloud development. On the other hand sfc
gradients will be weaker than they are this morning. Short range
ensemble guidance shows that the eddy will likely be weaker and
this should tip the scales to a clearer forecast. The best chance
for low clouds will be over the southern portion of LA county and
the Central Coast. Added in more low clouds for Oxnard plain
through Burbank for tomorrow based on latest model guidance. The
offshore trends will delay and weaken the seabreeze and this will
bring 2 to 3 degrees of warming to the area with the exception of
the Central Coast which will cool due to a more robust marine
layer presence. The Summer Solstice will occur at 151 PM PDT.

Friday will kick off a fairly dramatic warm up as a large and hot
upper high over the middle of the county expands westward. The
eddy looks a little stronger so probably a little more morning
low clouds across the coasts and into some of the lower vlys. By
noon the whole area will be clear. Heights will climb to ~588 dam
and max temps will warm 5 to 10 degrees across the interior and 2
to 4 degrees across the vlys. The coasts will still be under the
marine influence and max temps will not change much. Antelope Vly
residents will see max temps range from 100 to 103 degrees or
about 8 degrees over normal, and The Paso Robles area will also
near the 100 degree mark.

Saturday should be the hottest day of the heat event as SoCal
will be covered by the western half of an upper high`s western
half. Heights will rise to ~591 dam, but the fairly strong
onshore flow will remain in place resulting in a strong
temperature gradient from the coasts to inland. The high hgts
will really smoosh the marine layer down and create a very strong
inversion. Such strong inversions are hard to break down and this
could keep clouds at the beach all day long. The marine layer
will be under 1000 ft and this will keep it out of most if not all
of the vlys. The very steep inversion will also keep min temps
much warmer than normal right at the top of the inversion so
locations near 1000 ft in elevation will see these very warm
overnight lows. Look for 3 to 6 degrees of warming on Saturday
away from the beaches. Max temps across the interior will end up 6
to 12 degrees above normal while the vlys will be 2 to 4 degrees
above normal. There is about a 10% chance of 1" PWAT reaching into
LA County by Saturday afternoon. This moisture could impact the
Saturday night to Sunday marine layer, and overnight min temps.

.LONG TERM (SUN-WED)...19/152 PM.

Blended ensemble guidance shows some cooling on Sunday which could
be a reflection of the PWAT which is up to a 60% chance of more
than 1" by Sunday afternoon. The NAEFS forecast values for PW are
in the 90th to 99th percentile over Los Angeles County basically
from Sunday through Tuesday. This moisture will affect the marine
layer and temperature forecasts. There is even a small (10-20%)
chance of afternoon showers over the mountains.

The higher heights persist over the area Monday through Wednesday
but the broader area moves to the west and this position will
turn off the moisture to the area by late Tuesday. The temperature
differences will continue with the coasts sitting near normal
with a stubborn night through morning low cloud pattern in place
and the interior seeing well above-normal temps.

&&

.AVIATION...20/0051Z.

Around 2330Z, the marine layer depth was near 1900 feet deep at
KLAX. The top of the marine inversion was at 2500 feet with a
temperature of 19 degrees Celsius.

High confidence in the current forecast for the desert terminals.
Moderate-to-high confidence in the current forecast for coastal
and valley terminals. Higher confidence exists in flight
categories versus timing. Timing of arrival could much later than
forecast. Timing of clearing could be off by two hours later or
earlier.

There is a moderate chance of VFR conditions remaining through the
period at Los Angeles County valley terminals. There is a low-to-
moderate chance of conditions being one category lower than the
forecast, especially between 10Z and 14Z.

KLAX...MVFR conditions will spread into KLAX as early as 02Z or as
late as 09Z. There is a 10 percent chance of conditions being one
category lower than forecast around arrival. Any easterly winds
between 09Z and 17Z should be less than 7 knots.

KBUR...MVFR conditions could arrive as soon as 10Z, or as late as
14Z. There is a 30 percent chance of VFR conditions through the
period. There is a 30 percent chance of conditions being one
category lower than forecast around arrival.

&&

.MARINE...19/1253 PM.

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) winds are expected through Friday night.
Brief lulls in the winds during the mornings hours are possible.
Seas will be steep and choppy through Friday night. Conditions
are then expected to be below SCA levels Saturday through Monday
night.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. SCA winds and choppy seas will
persist through tonight, and again Thursday afternoon and
evening. For Friday through Monday night, winds and seas should
remain below SCA levels.

For the inner waters south of Point Conception, moderate to high
confidence in current forecast. For the western Santa Barbara
Channel, winds gusts will be at SCA levels each afternoon and
evening through Thursday. There is also a 30% chance of SCA level
wind gusts at times for western portions of the southern inner
waters Thursday evening. Elsewhere and otherwise over the
southern inner waters, winds and seas should remain below SCA
levels through Monday night.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory remains in effect until 3 AM PDT Thursday for
      zones 349-351. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Thursday 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 AM PDT Saturday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Rorke/jld
AVIATION...Hall
MARINE...Sirard
SYNOPSIS...jld

weather.gov/losangeles

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