Wind Advisory 70, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
939 AM PDT Wed Oct 9 2019

.SYNOPSIS...09/848 AM.

Temperatures will be below normal today, then will warm into
Saturday. A strong Santa Ana wind event will develop Thursday and
continue through Saturday with warm, very dry, and windy
conditions expected.

&&

.SHORT TERM (TDY-FRI)...09/937 AM.

A solid marine layer this morning with tops around 2000' in the
south and 1000' in the north. We're going to stay onshore today
with some gusty winds again in the Antelope Valley and surrounding
foothills. Low clouds will linger over the coastal waters and near
some beaches but otherwise sunny skies expected with temps a few
degrees cooler than yesterday. Local profilers confirming the
cooling in the boundary layer with temps down 4-8 degrees from
yesterday.

This evening we'll see a little northerly wind event in southern
SB County west of Goleta with some gusts to 30-40 mph. This will
temporarily push the marine layer away from SB County but into
Ventura and LA Counties. As the Santa Anas develop later in the
night the low clouds from Malibu to Ventura will be returned to
srn SB County but remain over srn LA County and the San Gabriel
Valley through Thursday morning.

The rest of the forecast looks on track with two days of strong
northeast winds across LA/Ventura Counties with the exception of
the San Gabriel Valley and the LA Coast south of the Hollywood
Hills. Latest hi res model guidance and gradients suggest peak
winds up to 75 mph in the mountains (including the western portion
of the Santa Monicas) and 55-60 mph in the Ventura Valleys. Will
likely be converting the mountain high wind watch to a warning
this afternoon and issue wind advisories for most of the
remainder of LA/Ventura Counties except for the SG and Antelope
Valleys. Parts of the Ventura Valleys will see brief warning level
gusts (Wiley Ridge in Central Ventura County and the hills around
Simi and Conejo Valleys).

***From previous discussion***

Speaking of that offshore wind event...it is shaping up to be a
strong one with both wind and fire weather impacts. A strong cold
sfc high pressure will develop in the Great Basin tonight and will
rapidly flip the onshore flow to offshore. (An impressive 14.4 MB
switch from this afternoons +7.8 MB onshore push to Thursday's
morning's -6.6 MB offshore push). In addition to the pressure
gradients there will also be a great deal of cold air advection
which will force the strong winds to the sfc and through the mtn
passes to the coasts and likely all the way out to Catalina
Island. Warning level gusts are a distinct possibility for the LA
mtns and the Santa Monica mtns. High end wind advisory containing
local warning level gusts are also very likely for the rest of LA
and VTA counties save for the San Gabriel Vly and the southern
portion of the LA county coast. All of the cold air rushing into
the area will drop the interior temps by 5 to 10 degrees except in
the Antelope Vly where max temps will come in 15 degrees lower
than todays. The adiabatic compression will bring slight warming
to the vlys and better warming to the coasts (where there will be
no marine layer) The Central Coast will also warm nicely with
light to moderate easterly flow.

Fire weather concerns will peak during this period.

At one time the winds Friday morning looked weaker than Thursday's
but now it looks like the winds will be similar if not a little
stronger in some places. The cold air advection will shut off and
there will be warming across the area.

By Friday afternoon there should be a noticeable decrease in wind
speeds as gradients and upper support weaken. Still breezy and
advisory level in some areas but quite a bit weaker than earlier.

One more thing of note. Min temps on Friday morning will be quite
cold in the wind sheltered areas due to the cool airmass and dry
air. The forecast for minimum temps in the Antelope Vly is very
difficult. If its windy min temps will be in the lower to mid 40s
if the winds go calm min temps will dip below freezing. Antelope
Vly residents need to be aware that there is chance of vegetation
damaging freezing temps Friday morning.

.LONG TERM (SAT-TUE)...09/316 AM.

All mdls show the gradients dropping off significantly on
Saturday morning. There will be canyon winds but they will be
below advisory levels. Wind sheltered areas will again wake up to
very cool temps. The offshore flow and slightly higher hgts will
create some warming everywhere except the coasts where an earlier
sea breeze will bring a little cooling.

Both the EC and the GFS forecast weak trofing over the state for
the SUN to TUE period along with increasing onshore flow. The
night through morning low cloud pattern will reestablish itself.
Max temps will slowly cool.

&&

.AVIATION...09/1636Z.

At 1630Z, the marine inversion at KLAX was based at 2300 feet.
The top of the inversion was 4000 feet with a temperature of
20 degrees Celsius.

Overall, moderate to high confidence in 18Z TAF package. Current
MVFR CIGs/VSBYs are expected to dissipate by 20Z although there is
a 20% chance that CIGs could linger as late as 22Z. For this
evening, there will be a return of MVFR conditions for coastal
sites south of Point Conception, but developing offshore flow
should clear out these clouds around sunrise. There will likely
moderate LLWS/turbulence through mountains passes Thursday
morning.

KLAX...Moderate confidence in 18Z TAF. There is a 30% chance that
MVFR CIGs could linger until 21Z. For tonight, moderate confidence
in return of MVFR, but low confidence in timing of formation (+/-
3 hours of current 03Z forecast) and dissipation (could be +/- 2
hours of current 13Z forecast).

KBUR...High confidence in 18Z TAF. there is a 20% chance that MVFR
VSBYs could linger to 20Z.

&&

.MARINE...09/936 AM.

For the Outer Waters, moderate to high confidence in current
forecast. For PZZ670/673, high confidence in current forecast with
Small Craft Advisory (SCA) level winds developing today and
tonight then winds and seas remaining below SCA levels Thursday
through Sunday. For PZZ676, high confidence in SCA level winds
today and tonight. For Thursday/Friday, there is a 40% chance of
SCA level northeast winds across PZZ676 then winds and seas
expected to remain below SCA levels Saturday/Sunday.

For the Inner Waters north of Point Sal, high confidence in
current forecast. There is an 80% chance of SCA level winds this
afternoon and evening. For Thursday through Sunday, winds and seas
are expected to remain below SCA levels.

For the Inner Waters south of Point Conception, high confidence in
current forecast. There is a 70% chance of SCA level westerly
winds across the western half of the Santa Barbara Channel this
afternoon and evening. For Thursday and Friday, SCA level
northeast winds are likely from Ventura Harbor to Anacapa Island,
Point Mugu to Santa Monica, and through the San Pedro Channel to
Catalina Island with northeast winds likely impacting northeast
facing harbors on Catalina Island (Avalon Harbor and Two Harbors).
For Saturday and Sunday, winds and seas are expected to remain
below SCA levels.

&&

.FIRE WEATHER...09/900 AM.

High confidence in a moderate to strong Santa Ana wind event
Thursday through Friday. The winds will be focused over Los Angeles
and Ventura Counties, and will peak Thursday mid morning to mid afternoon
with gusts between 45 and 70 mph. The winds should weaken Thursday
night and Friday, but only by 5 to 10 mph meaning the winds will
remain gusty. Santa Barbara and San Luis Obispo Counties will also
see peak east to southeast gusts in the 15 to 35 mph range,
especially Thursday night into Friday over interior areas.
Humidities will start off high over the coasts and valleys Thursday
morning with some marine layer influence, but high confidence in
widespread single-digit humidities by Thursday afternoon. These very
dry conditions will last through Sunday, and possibly through Monday
or Tuesday. Overnight recoveries will be poor, especially on
Thursday night with near zero recovery. Mild temperatures expected
on Thursday, with highs generally in the mid 70s to mid 80s in the
coasts and valleys. As a result, widespread critical fire weather
conditions are certain for Los Angeles and Ventura Counties where a
Red Flag Warning is in place. While winds will weaken significantly
Friday night into Saturday, there is a chance that the winds stay
just strong enough to extend the warning over the mountains. Over
San Luis Obispo and Santa Barbara Counties, elevated to briefly
critical conditions are likely Thursday and Friday, but a Red Flag
Warning is not expected at this time.

This is a potentially dangerous situation, with critical weather
and dry fuel conditions. If a fire were to start, the environment
will be favorable for rapid fire spread and extreme behavior. The
public should be urged to use extreme caution with any potential
fire ignition sources. Past fires have begun from things like
discarded cigarettes, metallic hedge trimmers, welding activities,
and campfires.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Wind Watch in effect from late tonight through Friday
      afternoon for zones 46-54. (See LAXNPWLOX).
     Red Flag Warning in effect from 3 AM Thursday to 6 PM PDT
      Friday for zones 240-241-244>246-253-254-288-547-548. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect from 3 PM this afternoon to 9
      PM PDT this evening for zones 645-650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Thursday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

A strong Santa Ana wind event is expected to continue into Friday
with 70 mph gusts possible. Critical fire weather conditions are
likely across a large portion of Ventura and Los Angeles counties.
There will be elevated fire weather conditions across Santa
Barbara and San Luis Obispo counties. In addition, sub-freezing
early morning temperatures are possible across the Antelope Valley
and other wind protected inland locations Friday and Saturday.

&&

PUBLIC...MW/Rorke
AVIATION...RAT
MARINE...RAT
FIRE...Kittell
SYNOPSIS...Sweet

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