Wildfire in California, May 30 to 31, 2021

Area Forecast Discussion
National Weather Service San Francisco Bay Area
455 PM PDT Sun May 30 2021

.SYNOPSIS...A robust warming trend begins today across the
interior, peaking on Memorial Day as high pressure strengthens
across the region. The heat begins to ease Tuesday and
temperatures return to near normal by Wednesday through the end of
the week.

&&

.DISCUSSION...as of 01:46 PM PDT Sunday...GOES-WEST Geocolor
imagery paints a transparent picture across the Bay Area and
Central Coast, with what little is left of the marine stratus
struggling to hang on to the Monterey Peninsula and portions of
the San Mateo Coast. The Bodega Bay Profiler continues to pick up
on the hot mid-level air mass which continues to expand this
afternoon in response to the nosing of the 585-590dm 500mb ridge
into Northern and Central California. A surface-level thermal low
is also deepening over the Northern Sacramento Valley this
afternoon resulting in widespread 80s and 90s F there. While not
on track for excessive heat in our CWA owing to less of an
influence from that synoptic feature, we will continue to be
heavily influenced by the mid-level ridge overhead. Its clockwise
flow has quickly mixed down to the lower-levels since this
morning, as is evidenced by our rapid marine stratus compression,
and the added solar radiation has helped to raise temperatures up
into the upper 70s and mid 80s all across the North and East Bay.
The north/northeast flow will also help to transfer some of the
hot air mass in the Central Valley into the Bay Area through the
overnight and into tomorrow. As such, are on track for poor
overnight RH and temperature recoveries for the interior.

Will be waking up Monday morning to min temps in the 50s across
much of the region and 60s and low 70s F along our peaks and
elevated terrain. Monday is set to be the hottest day of the year
thus far for much of the Bay Area, with the 500mb ridge peaking
in intensity at ~ 590-595dm. Its tilted- axis signature will allow
for the continuation of hot, dry Central Valley getting
transferred into the North and East Bay. Given the latest
deterministic solutions and SREF mean, in conjunction with the
overall heating trend that has been consistently picked up by
members and solutions alike for the past few days, have made
little changes in our afternoon forecast package to our max temps
for Monday. The strong mid-level ridge will keep the marine layer
compressed and limited in its reach to the coast. In turn, the hot
air mass over the Central Valley will continue to funnel into the
Bay Area and interior portions of the Central Coast. Widespread
upper 90s F will be observed in the interior, with areas over
1000 ft getting into the low 100s F. Will also observe RH values
between 30-35% at some of our highest peaks (e.g. Mt Diablo, Mt.
St. Helena, Atlas Peak, etc).

While winds and RH will not be meeting any critical fire
weather criteria, do want to remind people to continue to
practice fire safety during the Holiday by avoiding activities
that may initiate new wildfire starts. The added heat in the
North and East Bay Hills/Mountains will also increase the risk of
heat-related illnesses. As a reminder, a heat advisory is in
effect tomorrow starting at noon and lasting through 9PM. Be sure
to limit any outdoor strenuous activities during the hottest time
of the day. As for those who plan on escaping the heat by making
it down to the beaches should also practice beach safety as sea
surface temps are still running in the low 50s F and there is
always the risk for rip currents. In terms of coastal max temps,
some of the hot air is expected to mix down by tomorrow afternoon
but will be limited in its scope owing to the faint marine layer
influence. Expect stark temperature contrasts between the coast
and areas just a few miles inland (e.g. Sunset District vs Twin
Peaks, Santa Cruz Beaches vs Santa Cruz Mountains, etc) tomorrow,
with widespread low to mid-70s F along the immediate coast and
80s F along the coastal foothills. Warm temps will linger along
the higher peaks overnight Monday and into Tuesday morning with
min temps only getting down into the 60s F.

The upper-level ridge will remain the primary synoptic feature for
Northern and Central California through the rest of the week but
will become much more zonal and less amplified from Tuesday
morning onward. EC, GFS, and C ensemble members all hinting at the
weakened amplitude, while the latest EC/GFS deterministic
solutions both hint at the development of an upper-level low along
140W in response to the void left behind by the ridge. All of this
is to say that temperatures will become much more seasonal from
Tuesday through the end of the workweek next week, with coastal
temps returning to the 60s and low 70s F while the interior will
return to upper 70s to mid 80s F. The question for the forecast
package for next week will be how much on an influence the
upcoming upper-level trough will have on our temperatures. That
being said, the big picture is that members are signaling a
cooling trend following this Holiday weekend's heat event that
will return us to a setup that resembles our usual June Gloom.

&&

.AVIATION...as of 4:55 PM PDT Sunday...For the 00z TAFs. Expect VFR
to last as a building high pressure keeps stratus from returning
inland tonight. Winds will weaken into the evening, but some north
bay terminals may still see moderate winds aloft overnight, possibly
calling for some light LLWS. These winds will be around 15 kts at
2000 ft AGL with weak sfc winds. Expect mostly clear conditions
through the night with the exception for areas around the Monterey
Bay, which will see stratus move inland in the late night, but not
far enough to bump the terminals out of VFR. Monday continues the
VFR pattern with some breezy northwesterly winds returning in the
late morning.

Vicinity of KSFO...VFR with westerly winds backing off to around
15 kts this evening and below 10 kts overnight. Expect VFR though
the TAF period as stratus fails to return overnight. Winds become
more northwesterly for Monday afternoon at around 15 kts.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR through the TAF period as the
stratus fails to move far enough inland to affect MRY and SNS.
Northeastern portions of the Monterey Bay may see more stratus
move inland, but MRY and SNS will be far enough away from this
intrusion to stay scattered. Winds will remain mild overnight, and
look to stay below 15 kts for Monday afternoon.

&&

.MARINE...as of 04:52 PM PDT Sunday...Breezy to gusty northwest
winds will continue this evening with  stronger gale force gusts
over the northern outer waters through  Monday morning. This will
result in hazardous seas conditions for smaller vessels as winds
generate steep fresh swell. Winds will be slow to diminish, easing
by Monday afternoon. The sea state  remains predominately wind
driven along with a lighter mixed  northwest and southerly swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
             GLW...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm

&&

PUBLIC FORECAST: Diaz
AVIATION: Murdock
MARINE: AS

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