Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 210026

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
526 PM PDT Sat Jul 20 2019

.SYNOPSIS...20/235 PM.

Night through morning low clouds are expected over the coast
tonight into Tuesday. A strong area of high pressure will move
into the region Sunday yielding much warmer temperatures over
inland areas through the end of the week. There will also be a
slight chance of afternoon thunderstorms over the mountains and
deserts Monday and Tuesday.


.SHORT TERM (TDY-TUE)...20/228 PM.

The marine inversion early this afternoon was around 1400 ft deep
at LAX. Low clouds had cleared from most coastal areas early this
afternoon, with sunny skies prevailing across most of the region.
Little change can be expected for the rest of the day. Good
onshore gradients (NAM fcst +8.9 mb LAX-DAG at 00Z) will
contribute to some gusty S to W winds mainly for the foothills,
mtns and deserts into early this evening. Temps will be several
degrees below normal for most areas this afternoon. Highs in the
warmest vlys and lower mtns will reach the 80s overall, except
lower to mid 90s in the Antelope Vly.

A large upper level high over the central plains today will expand
into the western U.S. and form a strong upper level high over the
four corners region by late Sun. The center of this upper high will
move slightly north to the UT/CO border for Mon and Tue. The western
portion of the upper high will build into the forecast area thru Mon
then persist over the region thru Tue. 500 mb heights will increase
from 587-590 dm today to 591-593 dm by Mon then be around 593 dm on
Tue. The upper level flow will be from the SW through this evening
then turn more S to SE Sun thru Tue. This flow pattern should draw
some monsoonal moisture into srn CA by early next week.

The upper level ridging will help to lower the marine inversion down
to about 1500 ft tonight, then further to below 1000 ft Sun night
thru Tue. Night and morning low clouds and fog will affect mainly
the coastal plain and locally into the vlys tonight into Sun
morning, then just the coastal plain Sun night into Mon morning.
Even less coverage is expected Mon night into Tue morning, with just
the immediate Central Coast and southern coast of L.A. county
expected. Otherwise, mostly clear skies can be expected thru Sun
night, with some mid and hi level clouds moving into the area Mon
thru Tue for partly cloudy skies at times.

The 12Z NAM was indicating increased instability and moisture moving
into to the area on Mon. LI`s are forecast to drop to about -1 to -2
over the mtns and deserts Mon afternoon, and to as low as -3.5 in
the eastern San Gabriel Mtns. MUCAPE values drop to as low as 300-
600 J/kg Mon afternoon in these areas as well, and PWAT values
increase to near 1.35 inches. 850 mb dewpoints are also expected to
increase, and are forecast to be in the 6-7 deg C range Mon
afternoon. With the moisture in place combined with instability and
strong heating, there will be a slight chance of afternoon and early
evening showers and thunderstorms in the L.A./VTU/SBA County mtns
and Antelope Vly Mon afternoon into early evening. There will be
some residual moisture and instability over the area on Tue as well,
with a slight chance of an afternoon thunderstorm expected for
portions of the L.A./VTU County mtns and Antelope Vly. Any
thunderstorms that develop could produce heavy rain, gusty winds and
small hail.

Although onshore gradients should diminish slightly for Mon and Tue,
there will still be enough of an onshore push in the afternoon
and early evening for locally gusty S to W winds in the
foothills, mtns and deserts.

Temps will to warm to near normal Sun, near normal to several
degrees above normal Mon, and several degrees above normal for most
areas on Tue. The warmest vlys and lower mtns are expected to reach
into the upper 80s to mid 90s Sun, 90s to near 100 on Mon, and
mid 90s to about 102 on Tue. The combination of heat and some
higher humidities may eventually bring the need for a Heat
Advisory for the vlys and mtns for Tue.

.LONG TERM (WED-SAT)...20/230 PM.

The EC and GFS are in generally good agreement with the strong upper
level high drifting S to the four corners region by Wed, then
building slowly W and into srn CA by Sat. There may be some
monsoonal moisture over eastern parts of the forecast area on Wed,
then the moisture should remain just E of L.A. County Thu and well E
of the region Fri and Sat. There will be a less than 15 percent
chance of a shower of thunderstorm Wed afternoon over the eastern
San Gabriels, but POPs are too low to mention in the fcst.

The marine inversion is expected to be very shallow and probably
down to 400 to 600 feet deep during the period. Varying amounts of
low clouds and fog are still expected for the immediate Central
Coast and southern L.A. County coast each night and morning.
Otherwise, some mid and hi clouds should bring partly cloudy skies
at times to the area thru about Thu, then mostly clear skies are
expected Fri thru Sat.

Temps will peak on Wed with highs well above normal away from the
coast, then cool slightly each day thru Sat. Highs in the warmest
vlys and lower mtns should be in the upper 90s to 105 Wed, 90s to
around 100 Thu, 90s Fri, and upper 80s to mid 90s Sat. The Antelope
Vly should be in the low 100s each day for the most part. A Heat
Advisory may be needed for Wed, with some vly and mtn areas
possibly approaching excessive heat criteria.



At 2230Z, the marine layer depth was around 1550 feet deep at
KLAX. The top of the inversion was around 3000 feet with a
temperature near 22 degrees Celsius.

Low-to-moderate confidence in the current forecast. Higher
confidence in timing, less confidence in flight categories.

North of Point Conception...Predominantly, LIFR to IFR conditions
will likely spread in through 13Z. Less confidence in exists in
sub-VFR conditions for KPRB. There is a 20 percent chance of VLIFR
conditions between 10Z and 14Z. VFR conditions will develop as
soon as 16Z or as late as 18Z.

South of Point Conception...IFR to MVFR conditions will likely
spread into coastal and lower valley terminals through 13Z. There
is a chance of IFR conditions for valley terminals between 10Z and
15Z. VFR conditions could develop up to one hour later on Sunday.

KLAX...MVFR conditions will likely spread into KLAX as soon as 06Z
or as late as 10Z. VFR conditions should develop as soon as 17Z or
as late as 19Z.

KBUR...There is a 30 percent chance of IFR conditions and a 50
percent chance of MVFR conditions between 10Z and 15Z. Otherwise,
VFR conditions will persist.


.MARINE...20/155 PM.

For the Outer Waters... Conditions will remain below Small Craft
Advisory (SCA) level through at least Monday. There is a sixty
percent chance of SCA level winds across the northern and central
outer waters on Tuesday through Thursday and a thirty five
percent chance for the southern outer waters.

For the Inner and Nearshore Waters... Conditions will remain below
SCA level through at least Thursday.





The combination of heat and higher humidities may prompt the
issuance of Heat Advisories away from the coast for Tue and Wed.
Otherwise, no significant hazards expected.



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