Gale Watch 31, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
202 PM PDT Mon Jul 19 2021

.SYNOPSIS...19/502 AM.

High pressure over the Four Corners region will keep warm
temperatures in place across the interior through the week.
Onshore flow will keep coastal areas temperate as well as bring
breezy winds to the mountains and desert. Marine layer clouds will
likely return by Wednesday and last through the week.

&&

.SHORT TERM (TDY-THU)...19/200 PM.

Overall, 12Z models in good synoptic agreement through the short
term period. At upper levels, high pressure remains centered over
the 4 Corners area, wobbling about from day to day. Near the
surface, moderate onshore flow will prevail with some northerly
offshore flow during the overnight hours.

Currently, left over mid-level moisture, along with some ample
sunshine, is generating some cumulus buildups over the higher
terrain this afternoon. There may be enough "oomph" to generate an
isolated shower/thunderstorm over the San Gabriel Mountains and
eastern Antelope Valley this afternoon, but otherwise no
mentionable threat of convective activity.

For tonight through Thursday, forecast should remain rather
benign. As the upper high wobbles over the 4 Corners area, H5
heights lower slightly through Wednesday then increase a bit on
Thursday. So, the impacts on the marine inversion should be
limited and the inversion will remain quite shallow. With the
continued onshore flow, the stratus/fog should gradually become
more established each night, but still only impacting the coastal
plain and the lower coastal valleys. Any stratus/fog that develops
should dissipate rather nicely by the late morning hours each day.
With the location of the upper level high, will need to continue
to monitor for any influx of monsoonal moisture. At this time, the
flow looks to remain southwesterly enough through Wednesday to
keep any moisture east/south of the area. However on Thursday,
some moisture could filter in and will continue with a slight
chance of afternoon/evening showers and thunderstorms across the
San Gabriel Mountains and eastern Antelope Valley.

As for temperatures, anticipate minor day-to-day fluctuations,
based on the whims of the marine influence and the upper level
high. However, generally temperatures for most areas will hover a
few degrees above seasonal normals. With respect to winds, there
will be some locally gusty Sundowner winds each evening, but do
not anticipate any widespread advisory-level winds. Otherwise,
just anticipate the typical gusty southwesterly winds across
interior sections each afternoon and evening.

.LONG TERM (FRI-MON)...19/200 PM.

For the extended period, models do not look to be in the best of
agreement, especially with regard to the upper level pattern. The
GFS weakens the upper level high and gradually shifts it westward.
Conversely, the ECMWF weakens the upper level high, but shifts it
westward through the period. Net impact upon the forecast from
either solution will not be significant.

Through the weekend, onshore gradients are forecast to continue.
With H5 heights lowering as the upper level high weakens, the
marine inversion deepen a bit with stratus/fog making more of an
inland push each night. Otherwise, skies will vary between mostly
clear and partly cloudy, depending on how much moisture gets
caught up around the upper level high. Based on blend POPs, there
may be enough moisture/instability on Saturday to generate
isolated showers and thunderstorms over the San Gabriel Mountains
and eastern Antelope Valley. As for temperatures, looks for a
gradual cooling trend through the weekend.

&&

.AVIATION...19/1833Z.

At 1551Z at KLAX, the marine layer was 300 feet deep. The top of
the inversion was 2600 feet with a temperature of 25 C.

Good confidence in vly and inland TAFs.

Low confidence in coastal TAFs south of Point Conception. Moderate
confidence in central coast TAFs. LIFR to VLIFR conditions
expected on central coast later tonight. Marine clouds not
expected in coastal TAFs south of Point Conception, however there
is a 40 percent chance of marine clouds in coastal LA county with
IFR conditions.

KLAX...Low confidence for the overnight hours with a 40 percent
chance of IFR conditions with marine clouds. Good confidence that
there will be no east wind component greater than 4 kt.

KBUR...Good confidence in TAF.

&&

.MARINE...19/906 AM.

Through today, fairly high confidence that winds and seas will
remain below Small Craft Advisory (SCA) level. However, there is a
20-30% chance of low-end SCA level gusts this afternoon and
evening across the outer waters along the Central Coast. The
highest chance will be the far northern portion. NW winds will
strengthen across the waters on Tuesday with high confidence in
widespread SCA level winds from the Central Coast to San Nicolas
Island Tuesday afternoon through at least Thursday. There is a 40%
chance of Gale force gusts. Moderate confidence that SCA level
winds will expand into the western portion of the Santa Barbara
Channel each afternoon and evening.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 PM PDT Tuesday for
      zone 670. (See LAXMWWLOX).
     Gale Watch in effect from Tuesday afternoon through late
      Tuesday night for zones 670-673. (See LAXMWWLOX).
     Small Craft Advisory in effect from 9 AM to 3 PM PDT Tuesday
      for zone 673. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

No significant hazards expected.

&&

PUBLIC...Thompson
AVIATION...Sweet/Stewart
MARINE...Sweet/Stewart
SYNOPSIS...Stewart

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