Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 291714
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1014 AM PDT Mon May 29 2017

.SYNOPSIS...

A weak upper level ridge will breakdown and give way to an upper
level trough across the region early this week and persisting
over much of California through most of the week. Expect more
widespread low clouds and fog with a few showers possible Monday
and Wednesday in the mountains with patchy drizzle for a few
valley and foothill areas by mid week.

&&

.SHORT TERM...(TDY-WED)

Onshore flow is starting to increase in strength this morning as a
trough of low pressure along the West Coast approaches the area.
Surface pressure gradients are almost a full millibar more onshore
than this time yesterday. A 1800 foot deep marine layer has
stratus clouds well-entrenched this morning. Beach and coastal
locales may struggle to clear this afternoon, especially for the
Central Coast.

With onshore flow strengthening and the trough approaching, a
cooling trend will develop along a deepening marine layer into
Wednesday or Thursday. Marine layer stratus will likely stay
well-entrenched and become a staple of the weather pattern this
week. The beaches may struggle to clear each day through Thursday
as `May Gray` may turn to `June Gloom`.

Model solutions are still hinting at the potential for a few
elevated thunderstorms developing across the Ventura and Santa
Barbara County Mountains late this afternoon and this evening.
Latest NAM-WRF solutions have some 850-700 mb omega values over
the area in mention, as well as 700-500 mb CAPE values. The main
threat would be dry lightning and gusty and erratic winds. Some
clouds may also build up over the San Gabriel Range this
afternoon; however, there is less instability over the Los Angeles
County Mountains.

*** FROM PREVIOUS DISCUSSION ***

Low clouds are expected to redevelop and push inland across coast
and valleys tonight into Tuesday morning. With little change
synoptically, expat for slightly stronger onshore flow, expect a
degree or two of cooling across coastal areas, with little change
inland. An upper disturbance will move through the upper trough on
Wednesday bringing a more significant deep marine layer. Some
patchy drizzle has been added for the San Gabriel foothills. There
will be just enough lift with this trough that some showers will
be possible across the northern slope of the SBA/VTU County
mountains. Took out the chance for thunderstorms as the soundings
looked quite anemic in respect to convection potential for
Wednesday. High temps will bottom out on Wednesday with warmest
valleys reaching the mid to upper 70s with a few locations
reaching 80 degrees. Otherwise most areas will be the mid 60s to
lower 80s across the Antelope Valley.

.LONG TERM...(THU-SUN)

Both the GFS and ECMWF models are in fairly good agreement with
large scale features through next weekend. After the trough axis
moves through the region on Wednesday, broad NW flow aloft will
occur on Thursday then by Friday a weak upper ridge will form over
southern California briefly. Expect a modest warming trend
Thu/Fri across the entire region as heights and thickness lvls
rise. Onshore flow will weak late this week, but there should
continue to be night through morning low clouds. A weak upper low
will build in from the SW over the weekend which will help to
increase low clouds and begin another modest cooling trend. Models
seem to have a tough time dealing with systems coming up from the
SW. Will continue to go with cooler solution for the weekend.

&&

.AVIATION...29/1615Z...

At 1615Z, the marine inversion at KLAX was based at 1800 feet. The
top of the inversion was 4500 feet with a temperature of 22
degrees Celsius.

Overall, moderate confidence in 18Z TAF package. Current IFR/MVFR
conditions will dissipate by early afternoon with VFR conditions
for all sites this afternoon. For tonight, high confidence in
return of stratus/fog to all coastal/valley sites, but only
moderate confidence in timing and flight category.

KLAX...moderate confidence in 18Z TAF. For tonight, high
confidence in return of stratus, but moderate confidence in timing
(+/- 2 hours of current 04Z forecast) and flight category (40%
chance CIGs come in at MVFR levels).

KBUR...moderate confidence in 18Z TAF. For tonight, high
confidence in return of stratus, but moderate confidence in timing
(+/- 2 hours of current 08Z forecast).

&&

.MARINE...29/800 AM...

For the Outer Waters, high confidence in current forecast. Small
Craft Advisory (SCA) level winds will continue through Friday.
Each afternoon/evening, there will be a 30% chance of Gale force
gusts developing.

For the Inner Waters, moderate to high confidence in current
forecast. For the waters north of Point Sal, SCA level winds are
expected each afternoon/evening today through Friday. For the
waters south of Point Conception, conditions are generally
expected to remain below SCA levels through Friday. However, there
is a 30% chance of SCA level winds across the western half of the
Santa Barbara Channel during the afternoon/evening hours on
Wednesday and Thursday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 AM PDT Wednesday for
      zones 645-670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(WED-SUN)
No significant hazards expected.

&&

$$

PUBLIC...Hall/Kaplan
AVIATION...Thompson
MARINE...Thompson
SYNOPSIS...Kaplan

weather.gov/losangeles


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