Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 231745
AFDLOX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1045 AM PDT Sun Jul 23 2017

.SYNOPSIS...

Increased onshore flow will support slightly cooler conditions
today. A push of monsoonal moisture from the east may bring
isolated showers and thunderstorms, focused across interior areas,
Monday through Wednesday. Increased cloud coverage may bring
additional cooling for many areas Monday before a gradual warming
trend takes hold through much of the week.

&&

.SHORT TERM...(TDY-TUE)

Onshore pressure gradients are increasing across the today as a
weak trough of low pressure currently located near 39N and 127W,
or about 165 miles west-southwest of Mendocino, approaches the
North Coast of California. A couple of degrees cooling looks on
tap for today as a stronger onshore push should bring a more
enhanced sea breeze circulation. Temperatures have been tweaked
slightly for today in the latest update.

After today, the short-term forecast become more uncertain. Model
solutions are consistent in bringing a monsoonal surge northwest
into the area late tonight through Tuesday, but are backing off
slightly in the amount of the moisture and instability moving into
the area. High confidence exists in the moisture pushing across
the area, but the lift and instability is a bit more lacking
across the model solutions. Some model solutions hang on to K
index values in excess of 35 across the area, but favorable
lifted index values remain over the Mountains and Desert.
Precipitable water values are still healthy, in excess of 1.5
inches nosing into Los Angeles and Ventura Counties. For now, the
forecast remains unchanged, but future changes might occur.

With the monsoonal moisture moving in tonight and into Monday,
lower confidence exists in the marine layer stratus forecast
through Tuesday. The moisture moving in could play tricks with
the marine inversion over the next couple of days. The stratus
forecast the next several days could be overdone, and there is a
chance that the marine layer stratus could become very patchy.

*** FROM PREVIOUS DISCUSSION ***

Tuesday is much like Monday. The GFS has a decent monsoon TSTM
threat and the EC keep it to the East and South. GFS does not look
quite as aggressive as it does Monday so scaled the TSTM chc back
to the MTNS and then interior.

Due to the clouds and slightly lower hgts Max temps will be a
degree or two below normal each day but since its late July
afternoon temps will still feel quite warm.

.LONG TERM...(WED-SAT)

Wednesday is now looking like an active TSTM day. Both the EC and
the GFS agree that plenty of moisture will advect into the area.
If this is indeed what happens there will be TSTMs not just in the
mtns and the interior but over some of the coasts and vlys as
well. Since this is a brand new direction for the forecast have
only added a slight chc of TSTMs to the forecast for now but stay
tuned it could turn out to be a much more interesting day.

Kept Thursday dry but really there is enough moisture forecast to
add some convection. Will see if the mdls agree with this idea
later today before officially adding them to the forecast.

Friday and Saturday look dry as drier warmer air moves in over the
area. The GFS hints at some more monsoon flow on Sunday.

Otherwise the night through morning low cloud pattern should
continue. The hgts are high enough to keep the marine layer
smooshed low enough to keep the clouds out of the vlys. Max temps
will rise a little each day as the upper high expands and pushes
to the west. Hgts should be up to 595 DM by Saturday. There will
be slow warming trend but nothing too great. Max temps will start
out a couple degrees blo normal and end up a couple of degrees
above normal. There may well be little to no change in daily temps
for most of the coasts.

&&

.AVIATION...23/12Z.

At 0830z at KLAX... the inversion was around 1000 feet. The top
of the inversion was around 4400 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 continue to waft in and out of most coastal locations this
morning with conditions at KSMX VLIFR/LIFR at times. Conditions
will generally 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 through 17z. Otherwise and elsewhere VFR conditions
will prevail.

KLAX... Moderate confidence in the current TAF. IFR/MVFR conditions
will impact the terminal through 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 through 17z. Otherwise VFR
conditions will prevail.

&&

.MARINE...23/900 AM...

Winds and seas will 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...23/1028 AM.

Significant surf conditions may impact the Southern California
beaches late next week. Tropical Storm Hilary is expected to
strengthen to a major hurricane off the Mexican coast through
Midweek. As the system should clear the point near Bahia Tortugas
on Wednesday, a southeasterly swell will likely be generated and
push into the coastal waters beginning Thursday night or Friday
and peaking over the weekend. This swell will likely generate
high surf and strong rip currents on south facing beaches.
Isolated damaging sets of surf and beach erosion cannot be ruled
out for south-facing Los Angeles and Ventura County beaches.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through this 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
and Wednesday.

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/Rorke
AVIATION...Kj
MARINE...Sweet
BEACHES...Hall
SYNOPSIS...Munroe

weather.gov/losangeles


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