Gale Warning 29, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
217 PM PDT Wed Oct 23 2019

.SYNOPSIS...23/145 PM.

Weak to locally moderate Santa Ana winds will continue today over
portions of Ventura and Los Angeles counties. Strong Santa Ana
winds are expected Thursday into Friday leading to critical fire
weather conditions in many areas as well as hot temperatures near
the coast. Temperatures will start cooling on Saturday into early
next week.

&&

.SHORT TERM (TDY-SAT)...23/157 PM.

The next Santa Ana wind event is close at hand as surface
pressures over the Great Basin are starting to rise. The NAM,
ECMWF, and local high resolution models all predicting a LAX-DAG
gradient in the 8-9mb range and virtually all the EC ensemble
members are showing strong advisory level and even some warning
level winds at lower elevations. The GFS remains weaker, possibly
due to the lack of cold air advection, but has nudged closer to
the stronger solutions. So high confidence we're in for a strong
Santa Ana event for Thu and Fri. Have opted to go with strong
advisories for the valleys and coasts rather than a warning,
mainly due to the lack of cold air advection, though the usual
favored spots like Wiley Ridge in Ventura County and some of the
higher hills in Simi and Conejo Valleys will probably get isolated
60 mph gusts.

Models are mixed on the trends for Friday as some are similar and
others are slightly weaker. More likely we will see a 5-10 mph
drop in wind speeds Friday but still bordering on warning level
winds for the mountains.

Expecting temps to jump back up several degrees Thu across coast
and valleys with the downslope warming effects from the Santa Ana
winds. Coast and valleys will likely have similar temperatures
both Thu and Fri with widespread highs in the 90s. This puts the
coastal areas firmly in the heat advisory criteria as 90+ temps
are about 20 degrees above normal there and many homes aren't
equipped with AC. While just as hot in the valleys, the anomalies
there are "only" around 10-15 degrees and people are more used to
dealing with hot temps. So for now am limiting the extent of the
heat advisory to just the zones that border the ocean.

Still very warm Saturday but likely 5-10 degrees cooler for
coast/valleys, but more so for the coast as the onshore breeze
returns much earlier in the day.

.LONG TERM (SUN-WED)...23/212 PM.

Very low confidence in the forecast for early next week as models
are mostly holding onto recent polar opposite solutions. We are
seeing more of the ECMWF ensemble members drifting towards the
drier/windier GFS solution and today's deterministic EC solution
did scale back on the moisture and rain chances locally, though
the ensemble mean still does have 30-50 PoPs for Monday across
Ventura/LA Counties. The trends though do favor the
drier/winder/warmer GFS solution and the official forecast leans
strongly in that direction as well.

The GFS develops gusty northeast winds as early as midday Sunday
which in an unusual time for Santa Ana winds to develop. But this
mirrors the gradients as the GFS currently shows a LAX-DAG
gradient of around 0mb at 12z Sunday morning but then decreasing
to -7mb by 18z. So coast/valley temps Sunday/Monday have been
warmed a few degrees from earlier forecasts with the Santa Anas
returning. But this event will have much better cold air advection
and that will offset some of the usual downslope warming effects
at lower elevations but mountains and far interior valleys will
cool off with chilly morning temps.

Relatively quiet weather pattern Tue/Wed, though there's still a
fair amount of model disagreement in the upper air pattern and
resulting temps. Likely near to slightly above normal in most
areas under clear skies and typical diurnal winds with this
pattern expected to continue through the rest of next week
including Halloween.

&&

.AVIATION...23/1659Z.

At 1607Z, there was no marine layer at KLAX.

High confidence in CAVU 18z TAFs. There will be a 30% chance for
LLWS and UDDF across airfields across L.A. and Ventura County
Coast and valley locations, especially after 12z Thu.

KLAX...VFR conditions are expected through the 30-hour period.
There is a 30% chance for easterly wind component to exceed 8
knots.

KBUR...VFR conditions are expected through the period at this
time. There is a 30 percent chance of wind shear and turbulence
starting 10z Thu.

&&

.MARINE...23/207 PM.

Outer Waters...Winds will remain below Small Craft Advisory
thresholds through at least this weekend. There is a 30% chance
that SCA level gusts could occur across the western portion of the
northern outer waters of zones (PZZ670-673) this afternoon
through early evening. The exception would be the northern
portion of the southern waters (PZZ676) where the potential for
easterly Gale force gusts could occur across the northern portion
Thursday morning through mid afternoon hours.

Inner Waters N of Point Sal...Not anticipating any winds reaching
SCA levels through this weekend.

Inner Waters S of Point Conception...Winds will remain below wind
advisory levels through late Wednesday evening. A strong Santa
Ana wind event will develop pre dawn on Thursday. Northeast winds
could strengthen quickly to Gale Force winds as early as 5-6 AM
between Ventura and Malibu and out to the Channel Islands. A Small
Craft Advisory/Gale Warning has been issued for early Thursday
morning through the mid afternoon hours. Gusts to 35 knots will be
possible in areas mentioned. Otherwise expect moderate to strong
SCA level winds across the San Pedro Channel to Catalina Island.
Mariners should be prepared for possibly choppy seas across east
facing harbors including Avalon Harbor Thursday. There is a 60%
chance that SCA level gusts will continue through Friday morning
for the same areas. Mariners should exercise caution due to the
rapid increase in NE winds and possibility for impacts of wind
waves on east facing harbors.

&&

.FIRE WEATHER...23/121 PM.

Through Friday, a moderate to strong Santa Ana wind event remains
on track. Peak wind gusts between 45 and 65 mph are expected for
much of Los Angeles and Ventura Counties, where a Red Flag Warning
remains in effect. Santa Barbara and San Luis Obispo Counties
will see elevated to brief critical conditions, with peak winds of
20 to 40 mph, but a Red Flag Warning is not anticipated.
Humidities will lower to 2 to 9 percent and temperatures will
remain well above normal with highs generally in the 90s. This has
all the ingredients of a dangerous fire weather scenario, similar
to or worse than the recent October 10-11 event that produced the
Saddleridge Fire.

The fuels and vegetation are critically dry. The expected weather
will create an environment ripe for large and dangerous fire
growth, especially Thursday and Friday. We urge everyone to be
extremely cautious with any potential fire ignition sources. Fires
have started from things like cigarettes, camp fires, welding or
brush clearing equipment, and dragging towing chains.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect from 10 AM Thursday to 5 PM PDT
      Friday for zones 34>36-39>41-46. (See LAXNPWLOX).
     Wind Advisory in effect from 5 AM Thursday to 3 PM PDT Friday
      for zones 40-41. (See LAXNPWLOX).
     Wind Advisory in effect from 1 AM Thursday to noon PDT Friday
      for zones 44-45-53-547. (See LAXNPWLOX).
     High Wind Warning in effect from 1 AM Thursday to noon PDT
      Friday for zones 46-54-88. (See LAXNPWLOX).
     Red Flag Warning in effect from 1 AM Thursday to 10 PM PDT
      Friday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 2 AM to 5 AM PDT Thursday
      for zones 650-655. (See LAXMWWLOX).
     Gale Warning in effect from 5 AM to 2 PM PDT Thursday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect from 5 AM to 2 PM PDT Thursday
      for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

Warm and dry conditions expected Saturday but lighter winds.
Elevated to briefly critical fire weather conditions possible,
especially inland areas. Gusty Santa Ana winds are possible again
Sunday and Monday.

&&

PUBLIC...MW
AVIATION...Sweet/Kaplan
MARINE...Sweet
FIRE...Kittell
SYNOPSIS...Stewart

weather.gov/losangeles