High Wind in California, May 5 to 6, 2020

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1122 PM PDT Tue May 5 2020

Updated aviation section

.SYNOPSIS...05/808 PM.

Temperatures will continue warming through mid-week as high
pressure, clear skies and offshore winds dominate the area.
Thursday should be the hottest day of the week, with a few areas
reaching 100 degrees. Gusty northerly winds will continue through
Thursday morning for southern Santa Barbara County and the I-5
Corridor.

&&

.SHORT TERM (TUE-FRI)...05/902 PM.

***UPDATE***

Northerly gradients are pretty strong early this evening (e.g.,
SBA-SMX -4.7 mb and LAX-SFO -8.9 mb at 03Z). These gradients were
helping to drive strong and gusty NW to N winds below and thru
the passes and canyons of the SBA County S coast and mtns. The
strongest observed gusts have been in the 45-50 mph range W of
Goleta, with a peak gust of 51 mph observed at the automated
station SCE San Agustin (west of Gaviota). These winds will
continue overnight into early Wed morning. Gusty NW winds up to
50 mph are also expected in the VTU/L.A. County mtns overnight
into Wed morning, mainly along the I-5 corridor. A Wind Advisory
is in effect for all these areas overnight into Wed morning.

Elsewhere, gusty NW winds along the Central Coast will diminish
tonight. Gusty W to NW winds over portions of the Antelope Vly
will persist for a while overnight as well.

Otherwise, skies over the region were mostly clear with a few hi
clouds. Little change is expected overnight altho a few low clouds
and patchy dense fog cannot be entirely ruled out late tonight
along the immediate SBA County Central Coast.

***From Previous Discussion***

Hot and windy continue to be the primary weather themes this week.
Temps today jumped into well into the 90s in the valleys and
expecting even warmer Wed/Thu possibly to around 100 in the
warmest locations. Overnight lows will be warming up as well at
lower elevations, especially where it's windy. Winds will shift to
northeast Wed night into early Thu and favor more of the
LA/Ventura valleys and mountains, though locally gusty winds will
continue in SLO/SB counties as well, especially in the hills. The
warm Sundowners in srn SB County will likely push temps into the
80s and even low 90s well into the evening hours the next couple
days. So a very hot period next couple days, rivaling temps we saw
a couple weeks ago. Though not reaching official heat advisory
criteria in most areas by NWS standards the fact that daytime
temps will be 20+ degrees above normal, very close to or breaking
records, and being very early in the season it was felt that a
heat advisory would be appropriate for all coastal and coastal
valley zones both Wed and Thu. Thu likely will be the warmest in
most areas, especially those where northeast winds are favorable
such as LA/Ventura Counties. Though current forecast high are
already above most of the model guidance there is the potential
for even hotter temps should either gradients or upper support be
stronger than what the models have been showing.

Most areas should be marine layer free though models have been
hinting that some of the low clouds well off the Central Coast
could move onshore later tonight. This is probably 50/50 at best
given the low level winds being from the north/northeast so a low
confidence forecast on that.

As winds shift to northeast late Wednesday into Thursday there
could be some very low end advisory level gusts across parts of
interior LA/Ventura Counties but again not quite enough upper
support or even gradients at this point to go that high. The
breezes will keep overnight lows pretty warm in some areas and
it's likely we'll see some windier areas not dropping below the
70s.

A cooling trend will begin Friday as onshore flow returns. We'll
likely even see some marine layer clouds returning to at least the
LA Coast during the morning. Still a warm day as there's still a
pretty strong ridge overhead but should be a good 5 degrees or
more below Thursday levels for coast/valleys due to the earlier
sea breeze. Probably not much change or even slightly warmer in
the AV though as the onshore flow won't have much impact on temps
there initially.

.LONG TERM (SAT-TUE)...05/155 PM.

The ridge remains in place for most of Saturday but onshore
breezes should start to bring some temperature relief to far
interior areas. Still a pretty shallow marine layer but expanding
to cover all the coasts and some of the lower valleys by morning.
An upper level trough will replace the ridge Sunday into Monday
with the onshore flow expected to strengthen to around 9mb (LAX-
DAG) Sun/Mon. Marine layer won't be super deep but the strong
inversion in place and onshore flow may make for a very slow
clearing trend for coastal areas, especially from Malibu north.
Temps will be falling back into the 70s for coastal areas and
possibly back to normal by Mon or Tue in all areas. Gusty
afternoon winds could get close to advisory levels in the Antelope
Valley each day and the combo of those and likely still pretty low
humidities could lead to a couple hours of near critical fire
weather conditions there, though fuel moistures are still quite
high.

One interesting feature to watch is both the GFS and EC are
showing a very weak frontal passage late Monday into early Tuesday
with a few ensemble solutions even dropping some light rain
across nrn SLO County.

This cooler pattern appears to be here to stay at least for most
of next week with strong onshore flow each afternoon. A weak upper
level trough will persist just off the west coast and keep temps
near to perhaps even slightly below normal at times with marine
layer clouds pushing well into the valleys each day and slow/limited
clearing for the coast.

&&

.AVIATION...06/0620Z.

At 06Z, there was no marine layer at KLAX. There is a surface
based inversion up to around 1450 feet deep with a temperature
around 30 degrees Celsius.

High confidence in VFR conditions at all terminals except for a
chance of LIFR conditions at KPRB. Periods of moderate wind shear
and turbulence are possible at KSBA through 16Z, and Los Angeles
County valley terminals through 20Z.

KLAX...VFR conditions are expected through the period. Any east
winds are expected to remain less than 7 knots.

KBUR...VFR conditions are expected through the period. There is a
chance of moderate wind shear through 20Z.

&&

.MARINE...05/843 PM.

Overall, moderate to high confidence in forecast. Gusty northwest
winds will continue to persist through Thursday with good
confidence that the strongest winds will occur tonight and
Wednesday. These winds will generate widespread short-period and
steep seas, especially tonight and Wednesday. These conditions
will pose a risk for all small craft. Fairly high confidence in
gale force gusts along the outer waters along the Central Coast
southward to San Nicolas Island. Winds across the western Santa
Barbara Channel will likely exceed Small Craft Advisory (SCA)
level through late tonight, with a 30% chance of gale force gusts
at times.

Moderate confidence that winds will relax to below SCA criteria on
Friday through the weekend. With a return of the marine layer by
this weekend, there is a chance of dense fog impacting the waters
during the overnight through morning hours.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory in effect from 10 AM Wednesday to 9 PM PDT
      Thursday for zones 34>36-39>41-44>46-88-547. (See LAXNPWLOX).
     Wind Advisory in effect until 9 AM PDT Wednesday for zones
      39-52>54. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
      zones 645-650. (See LAXMWWLOX).
     Gale Warning in effect until 3 AM PDT Thursday for zones
      670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

No significant hazards expected.

&&

PUBLIC...MW/Sirard
AVIATION...Hall
MARINE...Sweet/Sirard
SYNOPSIS...Phillips/Smith

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