Wildfire in California, May 20, 2022

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1114 AM PDT Fri May 20 2022

.SYNOPSIS...Gusty northerly winds will persist across the
interior through Friday with elevated fire weather concerns
developing. Seasonably warm and dry weather continues for this
weekend into early next week.

&&

.DISCUSSION...as of 09:13 AM PDT Friday...Webcams and satellite
imagery show a nice start to your Friday with ample sunshine. The
bigger story near term are actually the winds and elevated fire
weather concerns. A look at pressure gradients around the region
reveal some impressive readings. The N-S (SFO-ACV) gradient is
sitting at -9mb and peaked over -10mb overnight. A rule of thumb
is anything over -6mb to -7mb will result in gusty winds over the
waters and limit low clouds sneaking into San Francisco Bay.
Needless to say, the strong N-S is producing strong winds over the
waters and hills. Mt St Helena peaked at 73 mph early this
morning. Other locations gusted in the 30-50 mph range. Will keep
the Wind Advisory as is for now. The northerly winds are also
ushering in drier air with humidity readings at or less than 30%.
The combination of gusty winds and lower humidity will result in
elevated fire concerns today.

No update needed this morning...

&&

.PREV DISCUSSION...as of 03:00 AM PDT Friday...Satellite imagery
showing mostly clear sky conditions over the region this evening.
Just a few passing high clouds can be observed over the Bay Area
which will continue to push southward across the Central Coast
through the remainder of the morning. Temperatures are also
running a few to as much as 10 deg F cooler compared to 24 hours
ago as a much drier air mass settles into the region. The dry,
northerly flow continues to produce gusty winds greater than 40
mph in the higher terrain across the interior, especially in the
North Bay and East Bay regions. With this, will continue the Wind
Advisory in effect through 2 PM Friday for interior North Bay
Mountains and much of the East Bay including the northern Diablo
Range and interior valleys. This said, the strongest wind gusts
remain in elevations greater than 2,500 feet as of this hour. Wind
speeds are anticipated to increase as a weak "inside slider" digs
southward across the Great Basin. Will monitor observations and
trends through the morning for any needed adjustments or
cancellations to the advisory.

Otherwise, look for slightly cooler temperatures across the region
this afternoon as a result of the cooler and much drier air mass
aloft. Still expecting interior areas to warm into the upper 70s to
lower 80s (mostly across the North Bay) this afternoon with
widespread 70s elsewhere. Meanwhile, onshore flow near the coast
will keep temperatures in the 60s. The main concern for the day will
be the very dry surface conditions with relative humidity dropping
into the teens and twenties for most locations away from the
immediate coastline. These dry conditions combined with the breezy
northerly winds will result in near-critical fire weather
conditions.

A gradual warming trend is then anticipated for the upcoming weekend
as high pressure over the eastern Pacific builds toward the coast.
While dry conditions will also prevail, wind speeds ease a bit and
overnight humidity recoveries will rebound. Thus, fire weather
concerns will lessen a bit through the upcoming weekend. Will
monitor to see if a shallow marine layer is able to develop during
the weekend which will help keep conditions in the 60s near the
coast while interior areas warm back into the 70s to low/mid 80s.

Forecast ensembles suggest a strengthening ridge and warming air
mass aloft heading into early next week as well. This will likely
bring interior areas into the mid/upper 80s and even lower 90s in
the region's warm spots for the first half of the upcoming week.
This warm-up looks to be short lived as troughing develops over the
Pacific Northwest and northern California late next week and into
the Memorial Day weekend. Thus, look for near normal temperatures
along with continued dry weather in the extended.

&&

.AVIATION...as of 11:13 AM PDT Friday...For the 18Z TAFs. VFR
conditions and mostly clear skies prevail across the region.
Northerly flow has advected very dry air into the region which
will allow VFR conditions to prevail through the TAF period. There
are some reports of HZ at area terminals which may lower vis
below 6SM for brief periods, but as onshore winds kick in this
afternoon, vis should improve. Moderate northerly to northwest
winds across terminals this morning, becoming breezy onshore this
afternoon, with gusty winds along the coast. Winds will slowly
diminish across the region after 03Z, becoming light overnight. A
burst of stronger NNE winds overnight in interior North Bay and
East Bay may bring some LLWS hazards.

Vicinity of KSFO...VFR. Light NW winds becoming breezy and gusty
this afternoon. Gusts expected between 25 and 30 kt. Winds will
diminish but stay breezy through Friday night, and become light
towards early Saturday morning. Skies remain VFR through the TAF.

KSFO Bridge Approach...Similar to KSFO.

Monterey Bay...Light to moderate onshore winds this morning,
becoming breezy and gusty this afternoon, especially down the
Salinas Valley. Skies likely remain VFR through tonight; however,
some models are hinting at some lower cloud development over the
bay early Saturday morning which may bring brief low CIGs.

&&

.MARINE...as of 10:46 AM PDT Friday...Strong northwest winds
across the waters through the day with gale force gusts in the
northern outer waters. Winds diminish Saturday but remain near
gale force in the northern outer waters. These  winds will
generate steep fresh swell at periods of 9 to 11  seconds through
the weekend as the sea state remains wind driven.  Winds are
expected to restrengthen early next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Wind Advisory...CAZ504-510-514-515
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             GLW...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Mry Bay from 1 PM

&&

PUBLIC FORECAST: MM/RGass
AVIATION: Lorber
MARINE: Lorber

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