Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 181630
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
930 AM PDT Wed Sep 18 2019

.SYNOPSIS...18/801 AM.

A trough of low pressure will cool temperatures through Thursday,
with some rebounding on Friday through the weekend. There will be
some overnight through low clouds and fog and then clearing in
most areas. Gusty northerly winds will continue across southern
Santa Barbara County.

&&

.SHORT TERM (TDY-FRI)...18/929 AM.

Weak marine inversion this morning again so despite a decent eddy
circulation only patchy low clouds around. Slightly cooler (1-3
degrees) most areas today with a stronger onshore flow and
lowering heights aloft but overall a pretty similar day as
yesterday. The trough passing through to the north will generate
increased northerly winds across the western third of the forecast
area leading to another round of low end Sundowners for srn SB
County. Possibly some advisory level gusts in the Gaviota area
otherwise generally 15-25 mph.

Cooler still Thursday as the trough deepens along the west coast
and likely a slightly stronger northwest push Thursday evening
across srn SB County.

Then turning significantly warmer Friday with northeast flow
developing.

.LONG TERM (SAT-TUE)...18/256 AM.

For the extended, models have the same general synoptic idea, but
differ noticeably in the details. So, confidence in the forecast
wanes noticeably after Saturday.

On Saturday, models indicate some slight increases in thicknesses
and H5 heights as well as weak gradients. So, temperatures should
increase a few degrees across the area. Skies will remain mostly
clear although there is a chance of some patchy stratus/fog
Saturday morning across the Ventura/LAX coasts.

On Sunday, models begin to develop an upper low just off the
Pacific Northwest. This will result in some lowering of
thicknesses and H5 heights and increasing onshore gradients. So,
temperatures will be a couple degrees cooler with the potential
for a bit more extensive coastal stratus across the Ventura and
LAX coastal plain. Additionally, southwesterly winds will increase
Sunday afternoon across interior sections.

For Monday and Tuesday, models drop the upper low south across
California with the low settling over far Southern CA by Tuesday.
The GFS is further east with the track of the upper low than the
ECMWF which leads to the greatly reduced forecast confidence. The
GFS solution would mean cool and unsettled weather for the area
with the possibility of some showers on Tuesday while the ECMWF
forecast would indicate warmer conditions with some weak offshore
winds. Given the difficulty of the models handling this feature,
will keep with idea of previous shifts, indicating cooling on
Monday and warming on Tuesday with no POPs. No doubt the details
of the forecast for Monday/Tuesday will change from model run to
model run over the next few days.

&&

.AVIATION...18/1152Z.

At 0740Z at KLAX, the marine layer was around 1000 feet deep. The
top of the inversion was near 1700 feet with a temperature of 21 C.

N of Point Conception...Hi confidence with VFR Conds through
early this afternoon. Low to moderate confidence with VLIFR/IFR
CIGs at KSMX with lower confidence for CIGs to develop at KSBP.
Moderate confidence for VFR conds at KPRB tonight into Thu
morning.

S of Point Conception...
Low confidence for MVFR Cigs to suddenly develop through 16z
across L.A. County. Moderate confidence for MVFR Cigs at KLGB
after 13z. There will be a better chance for more widespread MVFR
Cigs across Coastal TAF sites. Less confidence for KSBA. Moderate
confidence for Valley TAFs with MVFR or possibly brief IFR CIGs
late tonight into Thu morning.

KLAX...Low confidence in 12z TAF. There is a 40% chance that MVFR
cigs/vsby will develop between 13-16z. There is a 30 percent
chance of east wind component greater than 6 kt after 12Z. There
will be a 60% chance for easterly wind component over 8 kt
between 08-18z Thursday.

KBUR...Moderate confidence in 12z TAF. A 30 percent of MVFR haze
or CIGs thru 15Z. VFR through 02Z Thursday with IFR-MVFR cigs
likely after 09Z.

&&

.MARINE...18/917 AM.

Moderate to high confidence in the current forecast.

For the outer waters, Small Craft Advisory (SCA) level winds are
likely to persist through early Friday morning. Winds will
subside some on Friday, with a 40% chance of SCA gusts continuing
through Friday evening. The latest models now show winds near or
above SCA levels Sunday and Monday, strongest on Sunday.

Across the inner waters north of Pt Sal, there is a 60-70%
chance for (SCA) for NW wind gusts today and Thursday during the
afternoon and evening hours. Lighter winds are expected Friday
and through the weekend.

Across the Santa Barbara Channel, there is a 60 percent chance of
SCA level winds across western portions late this afternoon and
evening hours. SCA conditions are likely Thursday afternoon and
evening in the west channel. There is a 40% chance for SCA
conditions across the Santa Barbara Channel both Friday and
Saturday, with stronger SCA level gusts expected on Monday.
Otherwise, the remainder of the southern inner waters should
remain below SCA conditions through Monday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 3
      AM PDT Thursday for zones 645-650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Friday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

No significant hazards expected.

&&

$$

PUBLIC...MW/Thompson
AVIATION...Kaplan
MARINE...Sweet/Kaplan
SYNOPSIS...B

weather.gov/losangeles


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