Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 231156

456 AM PDT Sun Jul 23 2017

...Aviation discussion updated...


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 through the end of next



Today will be the easiest day to forecast through mid week. The
marine layer is near 1200 feet deep and the onshore gradients
(while still on the weak side) are about a MB stronger both to the
north and the east. Hgts will be a little lower as a weak 585 DM
upper low moves slowly to the nrn CA coast. Marine layer stratus
will cover the coasts and some of the coastal vlys in the morning
but it will be sunny everywhere by the after except maybe at a few
of the beaches. Max temps will be a degree or two cooler than ydy
but still in general above normal.

More marine layer clouds tonight across the coasts and locally
into the surprise there. But then the GFS and to a
lesser degree the NAM bring in a good slug of monsoon moisture and
instability to LA county. This is enough to justify a slight chc
or morning TSTMs for the AV and the LA mtns. IN fact if the GFS is
perfect there is a chance of TSTMs over the LA coasts and vlys as
well. Then (according to the GFS and somewhat according to the
NAM) monsoon moisture moisture will spread over all of the area
all the way to western SBA county including the waters, the coasts
and the vlys as well as the mtns and the rest of the interior.
There is lots of instability (esp over nrn VTA county) decent cape
and plenty of moisture if this comes to pass it will be a very
active weather day. But the EC paints an entirely different
picture and keeps almost all of the moisture to the south and east
perhaps allowing for a slight chc of a TSTM over the eastern San
Gabriel range. Have chc pops for the interior and slight chc
elsewhere except for Western SLO county should stay dry either

There should be enough mid level moisture and low level mixing to
prevent the marine layer to form Monday night but if the EC is
correct it will be more likely that there will be an overnight
stratus deck for the coast.

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.


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.



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...23/230 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...23/230 AM.

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.


CA...Beach Hazards Statement in effect through this evening for
      zones 40-41-87. (See LAXCFWLOX).


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.


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