Duarte Weather

000
FXUS66 KLOX 090316
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
816 PM PDT Thu Jun 8 2023

.SYNOPSIS...08/846 AM.

Some warming with a mix of clouds, sun, and mountain thunderstorm
threat through Friday. Another low pressure system will bring
cooler conditions and another increased threat of widespread
showers and thunderstorms over the weekend, potentially similar to
earlier this week. Warming to follow Monday through the middle of
next week.

&&

.SHORT TERM (THU-SUN)...08/815 PM.

***UPDATE***

Overall, a quiet early evening across the forecast district.
Latest satellite and surface observations indicate some patchy low
clouds across the area with mostly clear skies elsewhere. Current
sounding data indicates marine inversion at a depth in the
1500-2000 foot range.

Forecast-wise for the immediate short term, main challenge will
be the behavior of the marine layer stratus. The depth of the
inversion has decreased, but the inversion still is not too
strong. So, overnight, will expect the stratus to behave somewhat
chaotically with low confidence in areal coverage. However, all
coastal and valley areas will likely have a period of low clouds
overnight. Otheriwse, there will be some high clouds drifting
overhead.

Overall, current forecast has good handle on the immediate short
term. So, no significant updates are expected.

***From Previous Discussion***

Continued chaotic cloud pattern today, although clouds are
generally clearing away over Ventura and Los Angeles Counties
where the marine layer inversion is weakest (now only 1 degree
Celsius). To the north over Santa Barbara and San Luis Obispo, the
clouds are more persistent with a slightly stronger marine layer
inversion keeping the low-level moisture confined to the surface.
The inversion should strengthen a little overnight with a weak
high pressure ridge forming, but will still be very weak
especially over Ventura and Los Angeles Counties. As a result, the
low cloud pattern will likely not be very uniform with random
areas of clouds and clear skies. There is no great way to code
that into the forecast, so had to go with more clouds than will
actually materialize. For thunderstorms, clouds are starting to
form over the Ventura and San Gabriel Mountains, but they do not
look very convective. Still cannot rule out a late-bloomer
thunderstorm or two today or tomorrow, but more than likely not
much will happen. Temperatures will warm a little more on Friday
as that weak upper level ridge forms, but most of that warming
will be confined to the mountains and interior valleys or deserts.

A budding upper level trough, currently about 1200 miles west of
Oregon, will form into a closed low just off the central
California coast by late Friday Night. The vast consensus of
computer projections and their ensembles move that low right
through southern California over the weekend, in a very similar
track to the low that came through earlier this week. With enough
available moisture (precipitable water 1.0-1.2 inches), expecting
most if not all areas to receive measurable rain sometime over
the weekend, especially Saturday night. Convective parameters are
all really good over the mountains and interior valleys (peak
values of -6 lifted index, 41 K-index, 3000 MUCAPE, and 850
millibar dewpoints of 12 degrees C)...with the coastal and valley
areas about half of those valleys (which is still really good for
those areas). As such, there is a moderate threat for
thunderstorms over all areas, along with all the impacts they
usually bring (lightning, heavy showers, gusty winds, small hail).
Fairly confident of rain and thunderstorms over the most favored
areas which includes the mountains and interior valleys over
Ventura, Santa Barbara, and San Luis Obispo Counties. Rain totals
in those areas will likely fall in the 0.25 to 1.00 inch range,
with peak rates of 0.25-0.50 inches per hour (most of which fall
in 15 minutes or less). There is a moderate threat of isolated
flash flooding of creeks as a result. Far less confidence in the
details for all other areas, with highly variable rain amounts and
rates, and thunderstorm coverage.

.LONG TERM (MON-THU)...08/200 PM.

The aforementioned low will move to the east and out of the area
by later Monday, but some of the ensemble runs (EPS GEFS CMC) keep
the low in the area long enough for some wrap-around moisture to
bring additional showers through Monday. After that, conditions
look to return closer to normal through most if not all of next
week, with low clouds and fog and high temperatures generally in
the 70s (expected 80s in the desert).

&&

.AVIATION...08/2347Z.

At 2210Z, there was a very weak marine inversion, based around
3000 feet, at KLAX. The top of the inversion was 6200 feet with
a temperature of 13 degrees Celsius.

Overall, low confidence in 00Z coastal and valley TAFs, but high
confidence in desert TAFs. Low confidence in coastal/valley sites
is due to extreme uncertainties with possible development of
marine layer stratus. Current forecasts call for return of MVFR
and IFR CIGs to all sites, but confidence, as well as possible,
timing remains low.

KLAX...Low confidence in 00Z TAF. Timing of development of MVFR
CIGs could be +/- 4 hours of current 09Z forecast. There is a 40%
chance that CIGs will not develop. No significant easterly wind
component is expected.

KBUR...Low confidence in 00Z TAF. Timing of development of MVFR
CIGs could be +/- 4 hours of current 11Z forecast. There is a 40%
chance that CIGs will not develop.

&&

.MARINE...08/754 PM.

For the Outer Waters, high confidence in current forecast as
winds and seas are generally expected to remain below Small Craft
Advisory (SCA) levels through Tuesday. However, there is a 30%
chance of SCA level winds Saturday afternoon and night.

For the Inner Waters north of Point Sal and south of Point
Conception, high confidence in current forecast. Winds and seas
are generally expected to remain below SCA levels through
Tuesday. However, there is a 20% chance of SCA level winds
Saturday afternoon and night.

There is a slight chance of thunderstorms across the coastal
waters Saturday through Sunday. Any thunderstorms that develop
would be capable of producing brief heavy rain, gusty winds, small
hail and dangerous cloud to surface lightning. Also, waterspouts
could be possible.

&&

.BEACHES...08/921 AM.

Surf of 3 to 5 feet is expected on south facing beaches of L.A.
and Ventura Counties, with locally higher sets to 6 feet on some
beaches. There will be a high risk of rip currents.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

$$

PUBLIC...Kittell
AVIATION...RAT
MARINE...RAT
BEACHES...Sweet/Smith
SYNOPSIS...Hall/RK

weather.gov/losangeles

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

NWS LOX Office Area Forecast Discussion