Acton Weather

000
FXUS66 KLOX 212130
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
230 PM PDT Sun Jul 21 2019

.SYNOPSIS...21/130 PM.

Temperatures will warm to above normal across much of the region
this week and there is a slight chance of thunderstorms Monday
and Tuesday. Overnight and morning low clouds will weaken but
continue along the coast through the week though very patchy some
days.

&&

.SHORT TERM (TDY-WED)...21/215 PM.

Clear skies are over most of our land area today with the marine
layer stratus cleared away to the coasts. Its still quite cloudy
over the waters along the central coast. As mentioned before, an
upper level high pressure area is establishing itself over the
four corners region today and 500mb heights are locally rising to
about 592DM. Afternoon highs away from the coast are getting quite
a boost, with parts of the Antelope Valley already above 100
degrees.

The flow aloft will be coming from the south and southeast around
the upper level high pressure and it will bring bring in some
monsoonal moisture as a result. Precipitable water
values associated with this moisture will be in the 90th
percentile through Friday. Expecting this pattern to remove the marine
layer stratus south of Pt Conception for the next few mornings at
least. Marine layer low clouds will remain a daily feature along
the Central Coast. Mid- and high-level clouds will bring partly
cloudy skies to VTA and LA counties. There will be enough
moisture and instability on Monday afternoon to bring a slight
chance of thunderstorms over the Ventura County and eastern LA
County mountains. Temperatures will warm further, especially in
from the coast.

The main change on Tuesday will be that the onshore wind along the
south coast will weaken, taking away the natural air conditioning
and allowing the coastal temperatures to increase by several
degrees. The models are showing the gradient driving the winds to
lessen by about 3 MB. The marine layer stratus should be confined
to the Central Coast. Temperatures will rise everywhere except the
deserts which are already in the triple digits. There will be
just enough moisture and instability again Tuesday afternoon to
bring a slight chance of thunderstorms over the Ventura County and
eastern LA County mountains.

Wednesday still looks to be the warmest day of the week. LA
County`s San Fernando Valley and Santa Clarita Valley as well as
the San Luis Obispo County mountains will be near heat advisory.
Heights do not appreciably change so the inland areas will not
warm more, but will remain 3 to 6 degrees above normal with
triple digit heat in the deserts. Temperatures across he coasts
and valleys will jump 2 to 5 degrees. The valleys will see high
temperatures in the mid to upper 90s but there will be a
smattering of 100+ degrees readings in the warmer locations. The
beaches will see max temps near 80 but the interior sections of
the coast will be near 90. There is a slight chance of afternoon
thunderstorms again on Wednesday, but limited to the eastern
portion of the San Gabriel mountains in LA County.

.LONG TERM (THU-SUN)...21/228 PM.

Models agree that the four-corners high will persist through
Friday. Heights do not change much so interior temperatures will
continue to run 2 to 5 degrees above normal. Onshore flow should
pick up by Thursday helping to cool the coast and valley
locations (LAX-DAG goes back over 8mb). Marine layer morning low
clouds will slowly reform along the south coast.

For Saturday and Sunday the four-corners high will shift to the
west and settle over Southern California. This should further warm
the interior areas and valleys. The low level onshore flow is
forecast to increase and there should be more night through
morning low clouds and fog. These will combine to bring cooling to
the coasts and temper the effect from the higher heights.

&&

.AVIATION...21/2002Z.

At 1701Z at KLAX, the marine layer was 1000 feet deep. The top of
the inversion was around 3000 feet with a temperature near 23 C.

Low to moderate confidence in the 18z TAF package. The marine
clouds have cleared the coastal TAF sites with only south coastal
TAF sites showing a slight chance of afternoon stratus.

The marine layer depth may shrink tonight with some doubt
regarding formation on the south coast, but TAFs still show IFR
conditions overnight. Expect IFR conditions on the central coast
and clear skies elsewhere.

KLAX...Low to moderate confidence in 18z TAF. There is a 30
percent chance of VFR conditions through Monday.

KBUR...Good confidence in 18z TAF. VFR conditions expected through
the period.

&&

.MARINE...21/905 AM.

For the outer waters, conditions will remain below Small Craft
Advisory (SCA) level through at least Monday, except for a 50%
chance for local (SCA) conditions across the NW portion of the
northern outer water zone (PZZ670) Monday afternoon through
Tuesday night. There is a 50 percent chance of SCA level winds
winds expanding across the entire outer waters by Tuesday
afternoon through at least Thursday.

For the inner waters near Pt Sal, there is a 40 percent chance of
SCA level winds Tuesday and Wednesday. Otherwise, winds should
remain below SCA levels.

For the inner waters south of Point Conception, conditions should
remain below SCA levels through at least Thursday. However, there
is a 30 percent chance of SCA level winds in the western Santa
Barbara Channel Tuesday afternoon and evening.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

The combination of heat and higher humidities may prompt the
issuance of Heat Advisories away from the coast for Tue and Wed.
There is also a slight chance of afternoon thunderstorms over
Ventura and LA County mountains through midweek.

&&

$$

PUBLIC...jld
AVIATION...Sweet/Kaplan
MARINE...Sweet/Kaplan
SYNOPSIS...Kj

weather.gov/losangeles