Freeze Watch 2, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
354 AM PDT Mon Oct 11 2021

.SYNOPSIS...11/301 AM.

An area of low pressure over Oregon will drop southeast into
southern Nevada through tonight and bring cooler conditions
through Tuesday with widespread gusty to potentially damaging
north winds across the area through tonight. A warming trend will
establish for the remainder of the week as offshore flow develops
by Thursday. Overnight low temperatures will be very chilly in
wind-sheltered areas away from the coast through late week.

&&

.SHORT TERM (TDY-WED)...11/352 AM.

The latest satellite imagery shows a cold upper-level trough over
Oregon early this morning. This trough is progged to dig
southeast through Nevada today, bottoming out near the Mogollon
Rim late tonight. The inside slider trough is rather moisture
starved, but enough moisture and dynamics could slip into the
interior portions today as the trough scrapes the southern Sierras
and the Owens Valley to warrant a slight chance of showers. PoPs
remain in the forecast for the northern and interior portions of
the area. The best chance of any shower activity will be for the
northern slopes of the mountain up against the Ventura-Los
Angeles-Kern County lines, and along the interior slopes of the
San Gabriel Range. Shower activity cannot be ruled out for eastern
and southern Los Angeles County today. 700 mb temperatures drop
to -7 degree Celsius across eastern Los Angeles, which should drop
snow levels down to around 4000 to 4500 feet tonight.

The main story with this trough will be much colder temperatures
through Tuesday and gusty to potentially damaging winds across
the area. Temperatures will drop to between 10-20 degrees below
yesterday's values as an arctic air mass plunges south with the
trough. The cold air punching in will serve to add cold air
advection for the wind scenario. 850 mb winds increase to near
45-50 knots with a 115 knot mid-level jet streaming across Los
Angeles County this evening. The wind headlines remain majorly
intact for now. A few tweaks were made to the end times for the
interior portions as the latest forecast guidance suggest winds
decoupling sooner than initially expected. At least, widespread
advisory level winds are expected to develop through today with
damaging winds very likely for the Los Angeles, Ventura, and Santa
Barbara County mountains and the Antelope Valley. There is some
concern of damaging winds developing across southwestern Santa
Barbara County today. Speeds will be tweaked up some and mention
isolated gusts to 60 mph in these areas. Forecast model guidance
is impressive for KPMD and KWJF increasing sustained winds up to
between 42 and 50 knots, which are heavily in support of high wind
warning level winds developing across the Antelope Valley.
Blowing dust may be of a particular hazard today out in the Mojave
Desert, in addition to the possibility of downed trees and power
lines.

Winds will diminish tonight and into Tuesday morning as the trough
exits the region. A cold air mass spreading into the area could
bring the first frost to the interior valleys late tonight and
early Tuesday morning, but there remains a better chance for
Tuesday night and into Wednesday morning. Frost advisories will be
added to the forecast for tonight and into Tuesday morning for the
San Luis Obispo County Valleys and the Antelope Valleys, followed
by freeze watches for Tuesday night and Wednesday morning.

Another weak shortwave trough will brush the area on Wednesday and
Wednesday night. The northerly surface gradient should get some
reenforcement on Wednesday night, and there is a chance of gusty
northerly winds across southern Santa Barbara County on Wednesday
night. A wind advisory for any event on Wednesday seems less
likely at this time.

.LONG TERM (THU-SUN)...11/353 AM.

Upper-level ridging aloft will nose into the state from the west
as offshore flow is developing on Thursday. A warming trend is
looking more likely for Thursday through Saturday as offshore
pressure strengthen. ECMWF ensemble members seem to most
aggressive with the offshore push with the operational run
suggesting -5 mb KLAX-KDAG surface pressure gradients for Friday.
morning. As model solutions struggle with forecasting offshore
flow and the compressional heating that takes place, temperatures
in the coastal and valley areas on Thursday, Friday, and Saturday
were trended higher over NBM values and putting values above or
on the upper-echelon of the ensemble members. There is a chance
that critical fire threshold could met for late week as advisory
level Santa Ana winds develop toward the end of the week. A few
areas touching the 90 degree mark would not be surprising toward
the end of the week.

With the drier air mass spreading in and clearer skies, wind-
sheltered areas such as the interior valleys and portions of the
the Santa Ynez and Ojai Valley could see temperatures remain quite
cold overnight on Friday and Saturday nights. Additional
frost/freeze products may be needed for late this week as we get
closer to the event.

&&

.AVIATION...11/0044Z.

At 2317Z at KLAX, the marine layer was 700 feet deep. The top of
the inversion was around 1500 at a temperature of 23 degrees C.

High confidence in VFR conditions for all TAFs except for LA
County coastal sites. There is a 40% chance of no low clouds for
KLAX/KLGB/KSMO. High confidence in gusty N to NW winds on Monday,
but moderate confidence in wind speeds after 16Z which may be off
by 5-10 kt. Moderate to strong turbulence is likely after 18Z,
especially around higher terrain.

KLAX...Moderate confidence in TAF. There is a 40% chance of no low
clouds tonight. Any east wind component will likely be 5 kt or
less 09Z-16Z. There is a 40% chance of a north cross wind
exceeding 25 kt after 23Z Monday.

KBUR..High confidence in CAVU TAF. Gusty north winds may arrive as
early as 18Z.

&&

.MARINE...10/852 PM.

VERY DANGEROUS WINDS AND SEAS ACROSS MUCH OF THE WATERS MONDAY AND
MONDAY NIGHT. ALL MARINERS SHOULD SERIOUSLY CONSIDER STAYING IN
SAFE HARBOR UNTIL TUESDAY.

High confidence in widespread Gales and very steep large seas
developing and expanding through the day on Monday, peaking Monday
evening, then decreasing by Tuesday morning. Current Gale
Warnings will remain in play, although they are admittedly a few
hours early in the start time and late on the end times out of an
abundance of caution. There is a chance for a couple of hours of
Storm Force Winds (50 knots) from Point Conception to San Nicolas
Island. These winds will quickly build large and very steep seas
everywhere, which can easily capsize small and mid-sized vessels.
While the nearshore areas of Los Angeles and Orange Counties may
not technically reach Gale strength (34 knots), the winds will
easily approach 30 knots and the seas will be just as steep and
hazardous as if there were Gale Force winds.

After the Gales weaken early on Tuesday, gusty Small Craft
Advisory (SCA) winds will likely persist from the Central Coast to
San Nicolas Island through Wednesday or Thursday. There is a
chance that the western half of the Santa Barbara Channel will
also see these winds each afternoon and evening. While seas will
lower considerably from the Monday evening peak, widespread choppy
seas should be expected through at least Thursday.

&&

.BEACHES...10/852 PM.

A large and very short period wind swell will quickly come and go
on Monday. During the late afternoon and evening peak, expect
dangerous and steady breaking waves over most beaches with strong
rip currents. Moderate confidence on timing and heights. Surf
will decrease quickly on Tuesday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...High Surf Advisory in effect until 8 AM PDT Tuesday for zones
      34-35. (See LAXCFWLOX).
     Wind Advisory in effect until 11 PM PDT this evening for zone
      34. (See LAXNPWLOX).
     Wind Advisory in effect from 11 AM this morning to 11 PM PDT
      this evening for zones 35-36. (See LAXNPWLOX).
     Wind Advisory in effect from 11 AM this morning to 2 AM PDT
      Tuesday for zones 37-38. (See LAXNPWLOX).
     Frost Advisory in effect from 2 AM to 9 AM PDT Tuesday for
      zones 37-59. (See LAXNPWLOX).
     Freeze Watch in effect from late Tuesday night through
      Wednesday morning for zones 37-59. (See LAXNPWLOX).
     Wind Advisory in effect until 6 AM PDT Tuesday for zone 39. (See LAXNPWLOX).
     High Surf Advisory in effect from 8 AM this morning to 5 AM
      PDT Tuesday for zone 40. (See LAXCFWLOX).
     Wind Advisory in effect from 1 PM this afternoon to 9 PM PDT
      this evening for zone 40. (See LAXNPWLOX).
     High Surf Advisory in effect from noon today to 8 AM PDT
      Tuesday for zones 41-87. (See LAXCFWLOX).
     Wind Advisory in effect from 1 PM this afternoon to 6 AM PDT
      Tuesday for zones 41-44>46-87-88-547. (See LAXNPWLOX).
     Wind Advisory in effect from 11 AM this morning to 6 AM PDT
      Tuesday for zone 51. (See LAXNPWLOX).
     Wind Advisory in effect until 11 AM PDT this morning for
      zones 52>54. (See LAXNPWLOX).
     High Wind Warning in effect from 11 AM this morning to 3 AM
      PDT Tuesday for zones 52>54. (See LAXNPWLOX).
     High Wind Warning in effect from 11 AM this morning to 11 PM
      PDT this evening for zones 59-549-550. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 1 PM PDT this afternoon
      for zones 645-650. (See LAXMWWLOX).
     Gale Warning in effect from 1 PM this afternoon to 3 AM PDT
      Tuesday for zones 645-650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 AM this morning to 1 PM
      PDT this afternoon for zone 655. (See LAXMWWLOX).
     Gale Warning in effect until 6 AM PDT Tuesday for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (WED-SUN).

Sub-freezing overnight temperatures are expected Wednesday
morning across interior San Luis Obispo County, the Cuyama Valley,
and the Antelope Valley. Gusty Santa Ana winds and critical fire
weather conditions are possible Friday.

&&

PUBLIC...Hall
AVIATION...Stewart
MARINE...Sweet/RK
BEACHES...RK
SYNOPSIS...Hall

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