Frost Advisory 12, NWS Los Angeles, CA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
606 PM PDT Fri Oct 13 2017

.SYNOPSIS...

Gusty north to northeast winds will impact the area, along with
warmer temperatures through Sunday and possibly Monday. Cooler
temperatures and a possible return of the marine layer are
expected for the middle of next week.

&&

.SHORT TERM...(TDY-MON)

Light offshore flow today will increase Saturday as high pressure
builds to the north following the passage of the trough into the
northern Rockies. Winds tonight will again favor the srn SB County
and I5 corridor areas but like last night should remain below
advisory levels. On Saturday northeast (Santa Ana) winds will
increase, especially across LA/Ventura Counties. The usual favored
area from the Highway 14 corridor southwest through Camarillo and
10-20 miles on either side of that will see the strongest winds
both Saturday and Sunday. Winds will likely reach advisory levels
both days with a little let up late Saturday afternoon and
evening. The offshore gradient peaks early Sunday morning but with
very little upper support it's unlikely winds will reach warning
levels despite the 8+ gradient forecast by the NAM, which will
likely be more like 6mb in reality. Santa Ana winds should drop
off fairly quickly early Sunday afternoon and while there will
still be some offshore flow Monday winds should be relatively
light.

Temperatures were slightly warmer today but will ramp up more
Saturday before peaking Sunday and Monday with highs in the mid
80s to lower 90s for most coastal areas and mid to upper 90s in
the valleys. Probably the only areas that will see any cooling
Monday will be within a few miles of the coast, otherwise it will
be similar or slightly warmer as the upper ridge remains quite
strong and the air mass overall is actually warmer than Sunday.
May see a few low clouds Saturday morning across southern LA
County before the offshore flow kicks in by mid-morning.
Otherwise skies will be clear through Monday.

.LONG TERM...(TUE-FRI)

Not much cooling overall on Tuesday as the ridge only weakens
slightly. Pretty good onshore trend so coast/valleys will see some
cooling, more so closer to the beach, but still well above normal
for all but the immediate coast.

A lot of uncertainty after that as models have not been very
consistent the last several runs. Odds favor a slight cooling
trend Wed/Thu but still near to slightly above normal temps. On
Friday the GFS shows a really deep trough for this time of year
and ample moisture to drop some rain across the area. The ECMWF
just has a very weak trough passage Friday and no precip. Have
introduced some clouds and kept in the marine lyr and cooler temps
for Friday but leaving the forecast dry.

&&

.AVIATION...14/0104Z.

At 00Z, the marine layer depth was around 1000 feet deep at KLAX.
The top of the inversion was around 2500 feet with a temperatures
near 22 degrees Celsius.

VFR conditions are expected at all terminals, except for a chance
of IFR to MVFR conditions at Los Angeles County coastal terminals.
Periods of moderate turbulence and wind shear are possible at
all terminals after 05Z.

KLAX...There is a 40 percent chance of IFR to MVFR conditions
through 16Z. Otherwise, VFR conditions are expected throughout the
period. Any east winds that develop should be less than 5 knots.

KBUR...High confidence in VFR conditions throughout the period.

&&

.MARINE...13/100 PM.

Gusty Northerly Small Craft Advisory (SCA) winds will push closer
to the Central Coast into the evening and down to San Nicolas
Island. These winds should weaken on Saturday.

There is a possibilty for NE wind gusts of 20 to 25 KT near Port
San Luis on Saturday morning...but will probably not be
widespread enough to need a SCA.

Fog is likely in the Santa Monica Basin and San Pedro Channel once
again tonight into Saturday...with visibility below 1 mile
possible.

A moderate Santa Ana will affect southern California on Saturday
and Sunday. These winds will peak Saturday night into Sunday in
general, but confidence is low how they behave over the waters.
There is a 20 percent chance of SCA NE winds from Ventura to
Santa Monica on Saturday, a 60 percent chance Saturday night or
Sunday. 30 percent chance of these winds affecting Avalon Harbor,
but if they do, it should only be of the 10 to 15 KT variety.

&&

.FIRE WEATHER...13/215 PM.

Gusty north to northeast winds will impact the area through
Sunday. From this afternoon through mid-morning on Saturday,
north winds, gusting between 30 and 40 mph, are expected across
the Santa Barbara county mountains and adjacent coastal foothills,
the Interstate 5 Corridor, Santa Clarita Valley, San Fernando
Valley and the Santa Monica Mountains. With the winds, very dry
air will move into the area with minimum relative humidity in the
teens and single digits. This combination of gusty winds and low
relative humidity will result in critical fire weather conditions.

By late morning Saturday, the winds will shift to the northeast
with a moderate Santa Ana wind event expected Saturday and Sunday
for Ventura and Los Angeles counties. The northeast winds will
increase during the day on Saturday, peaking in strength Saturday
night and Sunday morning, before slowly diminishing Sunday
afternoon. Wind gusts between 35 and 55 mph can be expected. Along
with the wind, relative humidity will drop into the single digits
and low teens (with poor overnight recoveries). This combination
of gusty winds and low relative humidity will result in an
extended period of critical fire weather conditions for all of
Ventura and Los Angeles counties (except for the Antelope Valley)
Saturday and Sunday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning in effect until 10 AM PDT Saturday for zones
      239-252. (See LAXRFWLOX).
     Red Flag Warning in effect from 8 AM Saturday to 6 PM PDT
      Sunday for zones 240-241-548. (See LAXRFWLOX).
     Red Flag Warning in effect from 5 AM Saturday to 6 PM PDT
      Sunday for zones 244-245. (See LAXRFWLOX).
     Red Flag Warning in effect until 6 PM PDT Sunday for zones
      246-253-254-288-547. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 11 PM PDT this evening
      for zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 AM PDT Saturday for
      zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PDT Saturday for
      zone 676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK...(MON-FRI)
No significant hazards expected.

&&

PUBLIC...MW
AVIATION...Hall
MARINE...Kittell
FIRE WEATHER...Thompson
SYNOPSIS...B

weather.gov/losangeles