Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 201132
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
432 AM PDT Fri Sep 20 2019

.SYNOPSIS...20/217 AM.

Offshore flow is expected this weekend which will bring warmer and
drier conditions to the area through Sunday along with some gusty
north to northeast winds in wind-prone areas. After a brief cool
down on Monday, high pressure will bring warmer and drier
conditions Tuesday and Wednesday with the potential for more
widespread offshore winds.

&&

.SHORT TERM (TDY-SUN)...20/217 AM.

Overall, 00Z models in good synoptic agreement through the
period. At upper levels, trough will move across the Great Basin
today with a ridge building over the district today/Saturday then
the ridge will weaken and move eastward a bit on Sunday as another
trough develops off the coast. Near the surface, weak north to
northeast flow will prevail through Sunday morning with onshore
flow returning Sunday afternoon.

Forecast-wise, no major changes to previous forecast thinking.
Lingering deep moist layer is generating some partly cloudy
conditions across LAX county as well as western SBA county. Expect
these clouds to dissipate later this morning with sunny skies for
everyone this afternoon. For tonight through Sunday, skies will
remain mostly clear with north to northeast low-level flow although
there will be a chance of some patchy stratus/fog across the LAX
county coast during the night and morning hours.

As for winds, currently gusty north winds are continuing across
the Santa Ynez Range and the I-5 corridor. Later this morning, the
winds will shift to a more northeasterly orientation and continue
from the northeast through Sunday morning. Offshore gradients are
not overly impressive and upper level support is limited. So,
any noticeable northeasterly winds will occur across the mountains
and valleys. At this time, given the limited upper level support,
do not anticipate any concern about widespread advisory-level
winds.

As for temperatures, expect a nice warmup for all areas through
Sunday due to building upper level ridge and weak offshore
gradients. In fact by Saturday and Sunday, most areas will be 4-8
degrees (if not a little bit higher) above seasonal normals.

.LONG TERM (MON-THU)...20/217 AM.

For the extended period, 00Z models have the same general synoptic
idea, but differ noticeably in the details. For Monday through
Wednesday, both the GFS and ECMWF drop an inside slider across
the West Coast. However, the GFS is further east and more
progressive with the inside slider than the ECMWF. By Thursday,
both models have the slider moving over Texas with broad cyclonic
flow over the area.

So on Monday, onshore flow will increase across the area as the
inside slider moves across Nevada. Therefore, will anticipate a
good bit of cooling with most areas 5-10 degrees cooler than
Sunday. With the return of onshore flow, marine layer stratus
could possibly develop Monday morning although high resolution
models do not indicate much coastal stratus. So, will keep skies
mostly clear on Monday, but only with moderate confidence.

For Tuesday and Wednesday, the differences between the GFS and
ECMWF make for some forecast uncertainty. If the ECMWF is correct,
there is the potential for a decent offshore wind event as there
is good northeasterly upper level support. Conversely, the more
progressive GFS has much less upper level support and therefore
less potential for any significant offshore winds. Still too early
to get a good handle on which way to lean regarding the potential
for offshore winds. However either solutions will keep skies clear
Tuesday/Wednesday with temperatures generally 3-6 degrees above
seasonal normals.

For Thursday, both models indicate a return of onshore flow and
cooler temperatures.

&&

.AVIATION...20/1131Z.

At 0856Z at LAX, there was a deep moist layer up to 3500 ft with
no significant inversion.

N of Point Conception...Moderate to high confidence with 12z TAFs.
There is a 30% chance for IFR Cigs as KSMX between 09z-15z Sat.

S of Point Conception...Moderate confidence in 12z TAFs. There is
a 40% chance for MVFR Cigs at KLAX after 10z Sat. There is a 30%
chance for VFR conds at KLGB. There is a 20% chance for IFR/MVFR
Cigs at KOXR after 10z Sat.

KLAX...Moderate confidence overall for the 12Z TAF. There is a 20%
chance for IFR conds between 12z-14z this morning but MVFR CIGs
should prevail with scour out times within an hour of TAF.
Otherwise, VFR conditions should prevail thru Saturday morning.
except for a 30% chance for IFR/MVFR Cigs from 10z-16z Sat
morning.

KBUR...Hi confidence in the 12Z TAF with CAVU skies through the 24
hour period.

&&

.MARINE...20/157 AM.

Moderate to high confidence in the current forecast.

For the outer waters, there will be a 40% chance of Small Craft
Advisory (SCA) gusts this afternoon into the evening. There is a
60% chance for SCA gusts returning for late Sunday afternoon
through Monday.

Across the inner waters north of Pt Sal, wind gusts will approach
(SCA) level gusts but should stay just below thresholds. There is
a 40% chance for (SCA) this afternoon across the western portion.
There will be a 30% chance for (SCA) gusts Saturday and Sunday.

Across the Santa Barbara Channel, SCA level wind gusts are
expected to remain just below 25 knots across western portions
late this afternoon and evening hours. Therefore a 30% chance for
SCA conditions across the western Santa Barbara Channel this
afternoon. Otherwise, the remainder of the inner waters should
remain below SCA conditions through Monday.

&&

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

&&

.HAZARD POTENTIAL OUTLOOK (SUN-THU).

On Tuesday and Wednesday, there is a chance of a Santa Ana wind
event as well as elevated fire weather conditions.

&&

$$

PUBLIC...Thompson
AVIATION...Kaplan
MARINE...Kaplan
SYNOPSIS...RAT

weather.gov/losangeles


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