High Wind Watch 5, NWS Los Angeles, CA

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
822 AM PDT Tue Apr 21 2020

.SYNOPSIS...21/308 AM.

High pressure will build over southwestern California bringing
very warm and dry conditions for most of the week. High
temperatures will be 10 to 20 degrees above average in the warmest
locations. Gusty northerly winds will develop each evening across
the coastal waters, the Santa Barbara south coast and the
Interstate 5 corridor from Tuesday through Thursday.

&&

.SHORT TERM (TDY-THU)...21/821 AM.

***UPDATE***

Overall, current forecast looks on track for the immediate short
term. Latest satellite shows mostly clear skies for most coastal
and valley areas with partly/mostly cloudy skies across interior
sections and the San Gabriel Valley. Expect these clouds to
dissipate later this morning with sunny skies all areas this
afternoon. With the sunshine and upper ridge building overhead,
temperatures today will be noticeably warmer than the weekend with
many areas west of the mountains in the 70s today. As for winds,
currently have some gusty north winds across the Santa Ynez Range
and the Interstate 5 Corridor. Any advisory-level gusts are still
localized in these areas.

No updates are planned for the forecast this morning. For the
afternoon forecast package, will definitely consider wind
advisories for the north winds as the gradients do increase. More
on that with the afternoon discussion.

***From Previous Discussion***

Ydy's upper low is over Las Vegas and it is bringing just the
barest amount of cyclonic north flow to the north slopes of the LA
and VTA mtns creating cloudy conditions and a few nuisance
showers. The low will move further east and any remaining shower
activity will end. Lingering north flow will keep clouds along the
Kern county border. Otherwise a patchwork quilt of clouds and
clear covers the forecast area with the most clouds over SBA
county. The clouds will decrease in the morning and it will be a
mostly sunny afternoon. A ridge will build in during the afternoon
and hgts will rise to 576 DM. The onshore push to the east will
weaken (despite the diurnal curve) and the offshore flow from the
north will increase. The lack of clouds, increasing hgts and
gradients will all combine and lead to 3 to 6 degrees of warming
over most of the area and 5 to 10 degrees across the LA county
vlys, the Ojai Vly and the windier portions of the SBA south
coast.

The there will be 2 to 3 MB of northerly offshore flow tonight.
This will produce advisory level winds across the SBA south coast
and will either produce gust just above or just below advisory
criteria along the I-5 corridor.

Ridging and 584-586 DM hgts will persist over the area Wed and
Thu. Skies will be clear. There will only be very weak onshore
flow to the east (this grad may even briefly shift offshore around
dawn) and increasing offshore flow (both days) from the north. On
Wednesday all areas will see about 10 degrees of warming with
almost all csts and vly warming into the 80s only the Central
Coast will see sub 80 degree temps. There max temps are about 10
degrees above normal. Another 1 to 3 degrees of warming on tap for
Thursday.

Winds will be other issue. The LAX-BFL grad will reach -4.4 MB Wed
evening and the -5.6 MB Thu evening. The SBA-SMX grad will
reach -3.3 MB Wed evening and -3.9 MB Thu evening. The SBA-BFL
grad will reach -3.1 MB Wed evening and -4.5 MB Thu evening. These
gradients will create moderate advisory level wind gusts across
the SBA south coast, the I-5 corridor and the Santa Clarita Vly
Wednesday evening and overnight. Slightly stronger winds will
occur Thursday evening and overnight resulting in similar
advisories and likely additional ones for the VTA vlys, The San
Fernando Vly and the Santa Monica mtns. There is a chc that
advisory level winds will reach the Malibu strip.

.LONG TERM (FRI-MON)...21/322 AM.

Ridging will persist through Sunday and then flatten out. Hgts
will remain between 583 and 586 DM. Skies will be clear save for
some high clouds later Sunday and Monday.

Max temps will be main topic of discussion. Friday and Saturday
will be the warmest of the next 7. On friday there is offshore
flow from both the north and the east. The NAM even brings gusty
NE winds down to the coasts (although the NAM usually over does
the winds so not counting on that) still its going to make for a
very warm day. The coasts and vlys will warm to the 80s and up to
93 degrees. There will be some coastal cooling on Saturday as the
offshore flow from the east switches around to onshore but the
vlys and inland areas will remain just as warm. While there will
be breezy north canyon winds they will not be as strong and this
will allow overnight low temps to cool into the upper 50s to the
mid 60s which will offer good relief from the heat. Max temps both
days will about 20 degrees above normal.

Record highs for Downtown LA Friday and Saturday are 93 and 94,
respectively. So there's a chance those could be broken. It's
likely that some records will fall on both days.

Better onshore flow and slight lower hgts will knock max temps
down to the upper 70s and 80s across the coasts and vlys on Sunday

Skies will be clear except for possibly some dirty high clouds
that pass up and over the ridge and through the area.

Ensemble forecasts favor a little more cooling for Monday but if
the EC comes true it will be warm with increasing offshore flow.

&&

.AVIATION...21/1022Z.

There was no marine layer at KLAX.

Moderate confidence in the current forecast. There is a chance of
MVFR ceilings at coastal and valley terminals through 16Z.
Otherwise, VFR conditions will persist. Moderate wind shear and
turbulence is possible at terminals south of Point Conception.

KLAX...There is a 30 percent chance of MVFR ceilings through 15Z.
There is 40 percent chance of northerly cross winds greater than
10 knots between 15Z and 18Z. There is a 20 percent chance of
moderate wind shear and turbulence between 00Z and 04Z. No east
winds are expected through 07Z Wednesday, then any east winds will
likely remain less than 7 knots.

KBUR...There is a 30 percent chance of MVFR ceilings through 13Z.
There is a 20 percent chance of moderate wind shear and
turbulence between 14Z and 16Z and again between 23Z and 03Z.

&&

.MARINE...21/326 AM.

Moderate-to-high confidence in the current forecast for winds,
moderate confidence in the current forecast for seas. Widespread
Small Craft Advisory (SCA) conditions (winds and seas) will
continue today across much of the coastal waters and likely
linger into Friday.

There is a 60-80 percent chance of gales from near Point
Conception south to the San Nicolas Island and through the Santa
Barbara Channel this afternoon and evening, then reducing to 50-70
percent after late tonight. Less confidence exists for the Santa
Barbara Channel.

Although portions of the Santa Monica Bay may not see SCA level
winds, SCA level seas will likely affect much of the waters inside
the southern California bight.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 9 PM PDT Friday for zone
      645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT this afternoon
      for zone 650. (See LAXMWWLOX).
     Gale Warning in effect from 3 PM this afternoon to 9 PM PDT
      this evening for zone 650. (See LAXMWWLOX).
     Gale Watch in effect from this evening through Thursday
      evening for zone 650. (See LAXMWWLOX).
     Small Craft Advisory in effect until 9 PM PDT this evening
      for zone 655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PDT Wednesday for
      zone 670. (See LAXMWWLOX).
     Gale Watch in effect from Wednesday afternoon through late
      Thursday night for zone 670. (See LAXMWWLOX).
     Small Craft Advisory in effect until 11 AM PDT this morning
      BELOW 7500 FEET for zones 673-676. (See LAXMWWLOX).
     Gale Warning in effect until 9 PM PDT Thursday BELOW 7500
      FEET for zones 673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (THU-MON).

Gusty north to northeast winds may cause driving hazards at times
Wednesday through Thursday night. There is a high potential for
the first heat wave of the season that will peak later this week.
Highs temperatures in the Los Angeles County coastal and valley
areas could reach into the lower 90s by Friday and Saturday.
Overnight lows in the warmest areas will be in the mid 60s.

&&

PUBLIC...Rorke
AVIATION...Hall
MARINE...Hall
SYNOPSIS...Phillips

weather.gov/losangeles