Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 161057
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
357 AM PDT Mon Jul 16 2018

.SYNOPSIS...16/329 AM.

Temperatures will remain hot across the region through at least
another week though onshore flow will provide some overnight and
morning relief along the coast. There is a slight chance of
thunderstorms Wednesday and Thursday afternoon across the Ventura
and Los Angeles County mountains and the Antelope Valley.

&&

.SHORT TERM (TDY-WED)...16/330 AM.

Latest GOES-16 Fog Product Imagery indicated low clouds filling in
across the Central Coast and pushing in across the L.A. Basin.
Expect low clouds to fill in across all coastal areas in the next
few hours, and possibly reaching the coastal valleys as well as
the latest AMDAR sounding near LAX was around 1800 ft. The weather
pattern will change little today, except with the deeper marine
layer depth, a few valley temps should be a few degrees cooler
compared to yesterday. Highs will still be in the 90s, while the
Antelope Valley will continue to see triple digit heat.

Synoptically, the upper level ridge over southern Cal, will begin
to expand from the Eastern Pacific through much of California into
Texas. Although H5 heights will be strengthening some, the cooler
onshore flow will help to negate some of the warming. Therefore,
expecting similar or slightly cooler conditions today. The
onshore flow is expected remain moderately strong over the next
few days, which will keep coastal areas relatively mild, and help
from keeping coastal valleys from experiencing that triple digit
we saw a few weeks ago. Not much change expected for Tuesday,
except the upper ridge will continue to strengthen with a 596 DM
high over the region and onshore flow should be a bit weaker. So,
there will be a degree or two of cooling across valleys, yet still
remaining well into the 90s. Not much change for coastal areas and
similar triple digit heat for the Antelope Valley. Expect night
through morning low clouds once again for coastal areas, and if
the marine layer remains this deep, a few coastal valleys like San
Gabriel could see some patchy morning fog Tuesday.

Changes to the forecast should begin late Tuesday night into
Wednesday morning as the upper ridge begins to rotate from a
W-E orientation to a NW-SE position. This change will begin to
allow more mid-level monsoonal moisture to initially advect into
SE portion of SoCal, then push farther west driving the humidity
levels up and and a chance for afternoon and evening thunderstorms
over the Los Angeles, Ventura Mtns as well as the Antelope Valley.
One interesting thing the models are starting to pick up on with
this easterly wave developing Wed morning, are some embedded upper
disturbances within the upper flow which could bring showers and
possible thunderstorms across Los Angeles, Ventura and Santa
Barbara Counties as early as early Wednesday morning. I`m not
buying into this scenario just yet, and will let later shifts
make a decision to add precip for coast and valleys of areas S of
Point Conception Wed morning if models remain consistent with
this upper level feature. The convective parameters are much
better just east of L.A. County, but there should be enough
instability, to initiate storms over the mountains. Precipitable
Waters (PWAT) look to be around 1.5" which is pretty juicy. The
steering winds will be around 15 to 25 mph east to west which
should help keep storms moving along and keep flash flooding
potential at a minimum or isolated. if storms start training or
redeveloping over the same areas, then that could be problematic
for recent burn areas. With this easterly flow, would not be
surprised if a few storms that fire off over the mountains move
into the adjacent valleys and coastal areas late Wed afternoon and
evening. As far as high temps, there will be a few degrees of
cooling due to the added humidity and cloud cover expected.

.LONG TERM (THU-SUN)...16/330 AM.

Both the GFS and European Models remain in decent agreement
through the long period. With a similar synoptic pattern expected
on Thursday, there will continue to be a chance of afternoon and
evening showers and thunderstorms including the Santa Barbara
County Mtns and SBA interior areas like Cuyama Valley. The
steering flow if storms initiate will be SE to NW and should keep
showers limited to the mountains and deserts. Unless some moisture
gets drawn up over the coastal waters. Not anticipating that
though. High temps will be trending a few degrees higher as there
should be less in the way of clouds. This could actually be a
better convective day for the mountains with better clearing
preceding Thu afternoon.

Drying and additional warming is expected going into the weekend
and there continues to be the potential for a long- duration heat
wave from early the following week. Highest temperatures will be
100 to 107 degrees in the inland valleys and desert on Sunday
afternoon.

***From Previous Discussion***

By Monday, July 23rd, a 598dm high pressure center sits over the
high desert area of southeast California. There are good
indications that this giant high will not move much at all
through the end of July! By Monday our 950mb temperatures will be
close to 35 degrees C for inland valleys and 40 C in the desert.
Although this doesn`t appear to be a repeat of the early July
heat wave when some temperatures reached 117 degrees in the San
Fernando Valley, it definitely looks like a very long duration
event that builds and compounds heat impacts over time.

&&

.AVIATION...16/1056Z.

At 11Z, the marine layer was around 2000 ft deep at KLAX. The top
of the marine inversion was around 3500 ft with a temp of 27C.

North of Point Conception, low clouds were widespread on the
Central Coast and in the Santa Ynez valley. Conds were mainly
IFR to LIFR, with local VLIFR conds. Expect clouds to scatter
out in most areas by mid to late morning. Expect similar low
clouds conditions tonight/Tue morning.

South of Point Conception, low clouds were affecting most coastal
areas with IFR conds, except low MVFR conds across L.A. county.
Low clouds should clear by mid to late morning. However, mid and
high level clouds may disrupt the stratus field, possibly allowing
for earlier clearing. There is a chance that IFR cigs could push into
portions of the VTU County valleys, the San Fernando Valley and
the San Gabriel Valley for several hours this morning.

Expect widespread low clouds in coastal areas s of Pt Conception
tonight/Tue morning, with high IFR to low MVFR conds expected.
Once again, IFR cigs could push into the some valley areas for
several hours late tonight thru mid morning Tue.

KLAX...Low confidence in the the 12Z TAF. There is a 40% chance
that mid level cloudiness will disrupt the stratus field and conds
will scatter out as early as 14Z. There is a 20% chance that there
will be no low clouds tonight/Tue morning.

KBUR...Low to moderate confidence in the 12Z TAF. There is a
30-40% chance of IFR to low MVFR cigs between 12Z and 17Z
this morning, and again after 09Z tonight.

&&

.MARINE...16/257 AM.

Across the outer waters, fairly high confidence that Small Craft
Advisory level winds and steep seas in the southern two zones
(PZZ673 and PZZ676) will drop below SCA levels by mid morning.
However, there is a 30% chance of SCA level winds across these
areas again late this afternoon thru late tonight. Otherwise, SCA
conditions are not expected thru Fri.

For the nearshore waters north of Pt Conception and the inner waters
south of Point Conception, SCA conds are not expected thru Fri.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

An influx of monsoonal moisture could bring shower and
thunderstorm activity and a threat of localized flooding to the
mountains and desert Tuesday night through Thursday. Building heat
for inland valleys, mountains, and the desert through Sunday.

&&

$$

PUBLIC...Kaplan
AVIATION...DB
MARINE...DB
SYNOPSIS...Kj

weather.gov/losangeles



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