Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 230628
AFDLOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1128 PM PDT Sat Jul 22 2017

...Aviation discussion updated...

.SYNOPSIS...

A typical summer weather pattern will bring night through morning
low clouds and fog to the coasts and some of the valleys through
next Saturday, except for Monday into Tuesday when plenty of
monsoonal moisture will move into the area with plenty of
cloudiness. There will also be a slight chance of thunderstorms
for many areas Monday, and in the deserts and mountains on
Tuesday. Temperatures will be near normal to slightly above normal
overall through the end of next week.

&&

.UPDATE...

Forecast is on track this evening and no updates are planned.

Temps today at the coast were very close to yesterdays readings
and were a couple of degrees above normal. Valley and inland
temps warmed 3 to 6 degrees as warmer air aloft pushed into the
area. The 850 temps at KLAX rose 3 degrees C in the last 24 hours
while the 950 temps were unchanged.

Mondays convection is the big forecast question. Looking forward
to the 00Z run of the EC to see if it bends towards the active
fcst of the GFS/NAM or continues dry.

&&

.SHORT TERM...(SAT-TUE)

High pressure aloft centered over Oklahoma will continue to weaken
and recenter over the Southwest United States through early next
week. 500 mb heights will fall into Monday as a weak trough of
low pressure near 37N and 130W approaches the North Coast of
California. Onshore flow will increase later today and the marine
layer should deepen slightly tonight and into Sunday. Night
through morning stratus clouds should penetrate a little farther
into the valley areas late tonight or early Sunday morning. As a
result, a cooling trend will take shape into Sunday, best along
the coastal areas.

The forecast gets a little more complicated on late Sunday as
monsoonal moisture moves northwest into Southern California. Model
solutions are in good agreement that a decent monsoonal surge will
take place over Southern California through Monday night, then
start to dry out between late Monday night and Tuesday night. The
marine layer stratus forecast will get difficult and low
confidence should placed in the cloud cover forecast between
Sunday night and Tuesday night as the moisture moves into the
region. PoPs have been bumped up accordingly as convective showers
and thunderstorms could spill over into the coastal and valley
areas on Monday and Monday night. Precipitable water values
increase to near 1.50-2.00 inches by Monday afternoon. 850-700 mb
dewpoints and mixing ratios remain favorable supporting PoPs at
this time across the area.

The air mass should start to dry out as drier southwest flow
entrains into the air mass on Tuesday. Convective shower activity
should become confined to the mountains and desert on Tuesday and
Tuesday night. PoPs have been pretty much untouched for this
period.

.LONG TERM...(WED-SAT)

Ridging aloft to the east of the region will wobble west through
Thursday, then strengthen across the Desert Southwest. A warming
trend should take place for the latter half of next week. The
marine layer depth will shrink and onshore flow will weaken as
subsidence aloft presses down on top of the marine layer. 500 mb
heights increase and 1000-500 mb thickness values climb into late
week. Monsoonal activity will likely remain east of the area for
Wednesday through Friday.

The developing story could be tropical depression Nine-E currently
off the Mexican Coast near 10N and 99W. This tropical system is
expected to become more developed over the next several days,
possibly becoming a hurricane on Monday. While this system has a
moderately-high probability of producing high surf and strong rip
currents for Southern California beaches as early as next Friday,
there is still the possibility, albeit lower that remnant
moisture associated with the tropical system could move north into
the Southwest United States next weekend and into the following
week. Stay tuned as this developing system could be the main
weather story.

&&

.AVIATION...23/06z

At 05z at KLAX... the inversion was around 900 feet. The top of
the inversion was around 4500 feet with a temperature of about 29
degrees Celsius.

Overall... Moderate confidence in the current coastal and coastal
adjacent TAFs and high confidence elsewhere. IFR/MVFR conditions
will return to most coastal locations through 09z with the
exception of KCMA where these conditions will develop closer to
12z. KSMX will have VLIFR/LIFR conditions at times 08z-15z.
Conditions will clear to VFR between 18z-20z then similar
conditions and timing will return to the region after 24/04z.
There is a thirty five percent chance of IFR/MVFR conditions at
KBUR and KVNY 11z-17z. Otherwise and elsewhere VFR conditions will
prevail.

KLAX... Moderate confidence in the current TAF. IFR/MVFR conditions
will impact the terminal 09z-19z. Similar conditions will return
after 24/08z. Otherwise VFR conditions will prevail. East winds
greater than 7 knots are not expected.

KBUR... Moderate confidence in the current TAF. There is a thirty
five percent chance of MVFR conditions 11z-17z. Otherwise VFR
conditions will prevail.

&&

.MARINE...22/800 PM...

For the coastal waters, good confidence in current forecast.
Winds and seas are expected to remain below Small Craft Advisory
(SCA) levels through Thursday. There will be a slight chance of
thunderstorms Monday afternoon and evening across the entire
coastal waters.

A long period south-southeast swell from a forecasted hurricane
in the eastern Pacific is expected to spread across the coastal
waters next Friday through the weekend.

&&

.BEACHES...22/230 PM.

Significant surf conditions may impact the Southern California
beaches late next week. A tropical cyclone developing off the
Mexican coast will generate a long period southeasterly swell
across the coastal waters beginning next Friday and continuing
through the weekend. This swell will likely generate high surf and
strong rip currents on south facing beaches.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Sunday evening for
      zones 40-41-87. (See LAXCFWLOX).
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK...(TUE-SAT)
A developing monsoonal flow pattern will continue chances of
showers and thunderstorm across the mountains and desert Tuesday.

A significant surf event could develop as early as Friday as
swells from what could become Tropical Cyclone Hilary arrive at
Southern California beaches. High surf and strong rip currents
could develop Friday, possibly peaking over the weekend.

&&
$$

PUBLIC...Hall
AVIATION...Kj
MARINE...Gomberg
BEACHES...Thompson/Hall
SYNOPSIS...Sirard

weather.gov/losangeles



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