707
FXUS66 KLOX 171838
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1138 AM PDT Sun Aug 17 2025

.SYNOPSIS...17/222 AM.

Temperatures will warm a little each day through Tuesday, but
remain below normal with low clouds over coasts and valleys.
Gusty Sundowner and I-5 winds will continue each night, strongest
Monday through Tuesday. High pressure will quickly build over the
region over the middle to end of the week with several days of hot
conditions likely. Thursday and Friday look the hottest, when
many valleys and lower mountains approaching or exceeding 100
degrees. Monsoonal surges are favorable Wednesday through the end
of the weekend, with a chance of afternoon mountain and desert
thunderstorms.

&&

.SHORT TERM (TDY-WED)...17/843 AM.

***UPDATE***

The forecast is well on-track, and no changes have been made to
the ongoing forecast.

***From Previous Discussion***

The low pressure system just off the the Alaskan Panhandle that
has driven our recent 5+ day run of below normal temperatures will
move little through Tuesday. Couple that with stronger than usual
onshore flow and a deeper than normal marine layer, and the cooler
than normal run looks poised to last a few more days. Highs in
the 70s will be common over coastal areas, 80s over the valleys,
and 90s over the deserts. Despite the seasonally deep marine
layer, dense fog will be an issue on the Central Coast.

Winds will remain gusty over southwest Santa Barbara County each
night, likely peaking Monday and Tuesday Night. Posted a low-end
Wind Advisory for tonight, and will likely need some more after
that. Some winds winds will expand to the east and into the wind
prone areas of the eastern Santa Ynez Range starting Monday Night,
but does not look strong enough to need a Wind Advisory. Gusty
southwest winds also expected each afternoon over the Antelope
Valley and nearby foothills, as well as northwest winds through
the I-5 Corridor each evening, but neither should not reach Wind
Advisory levels.

.LONG TERM (THU-SUN)...17/333 AM.

***A SEVERAL DAY HEAT EVENT is coming Wednesday through at least
 the end of the week, with a HIGH RISK FOR HEAT ILLNESS AND FIRE
 DANGER. Now is the time to adjust any plans for strenuous
 outdoor activities in the valleys and mountains to the cooler
 morning hours or for another week. If you live in a high fire
 danger area in the mountains, review your evacuation plans and
 route and stay tuned to your local emergency officials.

High pressure aloft, currently parked over Arkansas, will quickly
shift to the west Monday and Tuesday, and settle into the four
corners by Wednesday. This high is strong with 500 millibar
heights of 597-599 decameters. This high looks locked to move very
little through at least Friday, and possibly through the weekend.
This is a major pattern shift with big weather changes coming to
our region.

In terms of temperatures, they will climb quickly and projections
are trending towards a fairly long duration 5 or so day heat event.
Look for highs to increase sharply from 5-10 degrees below normal
on Monday to around 10 degrees above normal by Thursday and
Friday (likely the peak of this heat event). Confidence is high
for this sharp warming trend inland of the coasts, with fairly
remarkable consensus in the ensemble projections through Sunday
(Aug 24). Overnight temperatures will also warm, with many areas
seeing lows only in the mid 60s to mid 70s, and foothill areas
look poised to not drop below the 80s or even 90s. There is a
chance that the lows will be even warmer with the influx of
monsoonal moisture (more on that is a bit). Heat Advisories for
many valleys and mountains are looking favorable over all four
counties, with a 40 percent chance of localized warnings focused
on the hottest valleys and foothills. Despite max temperatures
only being 10 degrees above normal, the risk for heat illness is
high for this event because 1) This is the very hottest time of
the year climatologically, 2) This heat is coming quickly on the
heels of an extended cool period, 3) Overnight temperatures will
be above normal, and 4) Humidity levels may be elevated due to the
Monsoonal push. Continued to push the official forecast well
above the NBM based on ensemble projections and historical
comparisons. Records are possible, but they are fairly high for
this stretch of time and may be just out of reach.

The coastal areas will be the trickiest. While onshore flow will
weaken, it stays onshore. So the marine layer will shrink in depth
and coverage, but may not go away. Many scenarios are in play,
ranging from dense fog hugging many coasts all day with mild
coastal temperatures, to low clouds and fog completely erroding
away with highs well into the 90s and Heat Advisories needed. The
current forecast takes a middle ground approach, and we will
likely not know which scenario will win until a day or two before
the event starts.

The monsoonal potential is also rising for the middle to end of
the week thanks to the textbook several-day four corners position
of the high. Models continue to trend up in the moisture
transport, with the majority of ensemble solutions showing
precipitable water values between 1.25 and 1.50 inches. This is
plenty of moisture to kick off afternoon mountain and desert
thunderstorms. Introduced 20-30 PoPs for showers and thunderstorms
Wed-Sat as a result. Coastal and valley areas also have chances,
but that will be determined by any convective disturbances that
rotate up from Mexico, which is too far into the future for our
models to see at this point.

&&

.AVIATION...17/1837Z.

At 18Z at KLAX, the marine layer was 2200 ft deep. The top of the
inversion was at 4400 ft with a temperature of 20 Celsius.

High confidence in CAVU TAFs for KPMD and KWJF with breezy
afternoon and evening SW winds.

Moderate confidence in TAFs for remaining sites. Low cigs/vsbys
will continue dissipating late this morning for coastal and
coastal valley sites, where low cigs/vsbys are expected to return
tonight -- onset within +/- 3 hours of forecast times. There is a
20% chance that low clouds do not re-develop at KSBP, KSMX, KSMO,
KLAX, and KLGB. Minimum cigs/vsbys may be off by one or two
categories.

KLAX...Moderate confidence in TAF. There is a 30% chance for
cigs/vsbys to become IFR tonight and Sunday morning. Any east wind
component should remain under 8 kts.

KBUR...Moderate confidence in TAF. There is a 30% chance for
cigs/vsbys to become IFR tonight and Sunday morning.

&&

.MARINE...17/129 AM.

High confidence in seasonably gusty NW winds across the waters
beyond 20 miles from shore between the Central Coast to San
Nicolas Island. Small Craft Advisory (SCA) conditions will be
common this week, except for some morning lulls. Localized Gale
Force gusts to 35 knots may occur in the evening hours tonight
from Point Conception south to San Nicolas Island in the late
afternoon through late night hours tonight and Monday.

The nearshore Central Coast waters will see SCA level winds each
afternoon and evening into at least mid-week.

The western Santa Barbara Channel will see periods of SCA
conditions during the late afternoon and evening hours from Sunday
afternoon through at least mid-week. Highest chances for winds to
spill into the eastern portion exist in the afternoon and evening
Monday and Tuesday.

All areas will see choppy seas from these winds in the late
afternoon through late night hours.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory in effect from 6 PM this evening to 6 AM PDT
      Monday for zones 349-351. (See LAXNPWLOX).
     Fire Weather Watch in effect from Wednesday morning through
      Saturday evening for zones 288-375>382. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect from 5 PM this afternoon to
      midnight PDT tonight for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Tuesday for
      zones 670-673-676. (See LAXMWWLOX).

&&

$$

PUBLIC...Kittell/Cohen
AVIATION...Cohen/Lewis
MARINE...Lewis
SYNOPSIS...RK

weather.gov/losangeles

Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox