Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 111242
AFDLOX

Area Forecast Discussion...CORRECTED
National Weather Service Los Angeles/Oxnard CA
542 AM PDT Tue Aug 11 2020

.SYNOPSIS...11/237 AM.

There will be less and less morning low clouds each day until they
disappear entirely Saturday morning. Thursday will be partly to
mostly cloudy as high clouds stream overhead. A warming trend
will bring daytime highs to near normal by Wednesday, then a
heatwave will bring widespread temperatures of 100 degrees or more
Friday through the weekend, with 80s for coastal areas.

&&

.SHORT TERM (TDY-THU)...11/541 AM.

Not too much to talk about over the next two days. The area will
be under dry SW flow that is moving through the inflection point
between an upper high to the SE and and an upper low to the NW. A
1000 ft marine layer pushed ashore by a 3 to 4 MB push both to the
north and east has brought low clouds to most of the coasts and
some of the lower portions of the vlys. Visibilities are pretty
good along the coast but the vlys will likely see some patchy
dense fog under the stratus. There will likely be little change in
the clearing pattern this afternoon with total clearing south of
Pt Conception and clearing with the exception of a few beaches
across the Central Coast. Offshore trends and no eddy will reduce
the amount of low clouds on Wednesday morning. It is likely that
there will only be morning stratus across the LA south coast and
the immediate Central Coast. There will be some warming today but
much more widespread warming on Wednesday. Max temps Wednesday
will be near normal.

Things will be a little different on Thursday. There will likely
be a similar coverage of low clouds although it is pretty easy to
imagine the LA coast remaining low cloud free. It will be clouds
of another type that needs focusing on. The flow pattern around
the upper low to the west of the Central Coast and the
strengthening upper high to the ESE will start out near hurricane
Elida which will be about 550 miles to the SSW of LA. The flow
will entrain quite a bit of mid and high level moisture from Elida
and will make skies partly to mostly cloudy across LA and VTA
counties with lesser amounts of clouds over SBA and SLO counties.
The NAM GFS bring actual rain to VTA and ESP LA counties during
the morning and afternoon. The EC and a the majority of the
ensemble members are dry which makes sense given the total lack of
dynamic lift. The forecast is dry but still have to keep a
mindful eye on the evolution of the moisture plume. There will
likely be another 2 to 3 degrees of warming but if the high clouds
are thicker or more widespread it`s possible max temps will not
rise much at all.

.LONG TERM (FRI-MON)...11/334 AM.

All four days of the xtnded period will be dominated by the
temperature forecast. The upper high will move to the west and
envelop the southern half of the state. Hgts will be between 594
and 596 DaM through the period. The N/S and E/W gradients will
play a major role in this warm up and unfortunately there is not
mdl consensus with the gradient forecast.

The EC is consistently 1 to 2 MB more offshore than the GFS both
from the north and the east. The EC has actual offshore flow from
both north and east starting Friday morning and keeps it offshore
continuously all through way through late Sunday morning. The GFS
is never offshore to the east with only very weak onshore flow
forecast in the morning and about 3 MB onshore in the afternoon.
The GFS does have offshore flow from the north every morning but
does forecast onshore flow in the afternoon. There is no upper
support so aside from local gusts across the SBA south coast and
perhaps the I-5 corridor there really will not be much in the way
of canyon winds.

It looks like Saturday will be the warmest day as it will have
the most offshore flow. Friday will have 3 to 6 degrees of warming
and Saturday will add another 2 to 4 degrees to that. The Central
Coast may even warm a little more on Sunday. Saturday`s max temps
will be 8 to 12 degrees above normal for most areas with almost
all non coastal areas experiencing triple digit heat. Heat
advisories with (depending on how warm the overnight lows are
forecast) possible heat warnings are looking very likely.

The thing of note is that the current forecast favors the cooler
the GFS solution. If the EC`s gradient forecast is the correct
one max temps across the vlys and esp the coasts will need to be
warmed further.

The lack of winds will help keep this event from producing
critical fire wx conditions. The SBA south coast will be the area
most at risk for enhanced fire behavior but the current humidity
forecast for that area and the rest of the forecast area is just
high enough to preclude major fire danger.

Monday will cool some across the vly and esp the coasts as there
will be onshore trends which will bring an earlier seabreeze to
the coasts and vlys. The interior will likely remain very warm
with little or no cooling.

&&

.AVIATION...11/1211Z.

At 0822Z at KLAX...The marine layer was 1100 ft deep. The top of
the inversion was near 2000 feet with a temperature of 22 deg C.

High confidence in valley and inland TAFs.

Moderate confidence in coastal TAFs through 18Z, then good
confidence. There is a 30% chance of 1/2SM FG VV002 for sites
north of Point Conception. VFR transition may occur +/- 30 minutes
of forecast time. There is a 30% chance of IFR cigs 13Z-16Z at
KLGB.

KLAX...Moderate confidence in TAF through 18Z. There is a 20%
chance of 2SM OVC004 through 15Z. VFR transition may occur as late
as 1730Z. There will be no east wind component greater than 4kt.

KBUR... High confidence in CAVU TAF.

&&

.MARINE...11/146 AM.

Good confidence that winds and seas will remain below Small Craft
Advisory (SCA) level through Thursday across all the waters.
However, there is a 30% chance of SCA level gusts during the
afternoon and evening hours each day from Point Conception to San
Nicolas Island. Winds look a bit stronger over these
waters on Friday and Saturday, but still moderate confidence in
SCA level winds at best.

Patchy fog, locally dense with visibility under one mile, will
likely continue through mid-week across all the waters.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

Triple digit high temperatures and very warm nights will bring
the potential for excessive heat over many areas Friday through
Sunday and possibly Monday. Otherwise, no significant hazards
expected.

&&

$$

PUBLIC...Rorke
AVIATION...Stewart
MARINE...Stewart
SYNOPSIS...30

weather.gov/losangeles


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