Small Craft Advisory 202, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1020 PM PDT Mon Oct 19 2020

.SYNOPSIS...Low humidity will continue in the hills through the
week, as will occasional moderate and gusty offshore winds at the
higher elevations of the North Bay, and locally into the East Bay
and Santa Cruz Mountains. This will result in heightened fire
weather concerns from Monday Night through much of the week.
Little temperature change is forecast for Tuesday and Wednesday,
followed by from Thursday through Saturday. No precipitation is
expected with the potential for a strong offshore wind event later
in the upcoming weekend or early next week.

&&

.DISCUSSION...As of 8:55 PM PDT Monday...Primary forecast concern
throughout the remainder of the week and into next weekend will
be increasing offshore winds and continued dry conditions at the
higher elevations of the SF Bay Area, resulting in periodic
critical fire weather conditions in the hills. See Fire Weather
Discussion below for details.

The cooling trend that began yesterday continued today as marine
air continued to gradually filter inland. Cooling today was
limited to just a few degrees in most inland valleys and in the
hills, but coastal areas and coastal valleys experienced another
5-10 degrees of cooling. Even with cooling over the past few days,
most locations remained warmer than seasonal averages today. The
exception - Downtown San Francisco's high of 69 today was right at
their normal for the date.

The rex block currently centered offshore along 140W is forecast
to retrograde slightly through midweek, allowing for a slightly
cooler airmass to develop over our region. Offsetting this
cooling effect will be drier air as moderate offshore winds
develop in the hills by late tonight and Tuesday. Thus, expect
temperatures to remain near persistence through midweek.
Regionwide cooling is then expected from Thursday through Saturday
as an upper trough deepens to our east over the Intermountain
West. This deepening trough will also result in increasing
offshore winds in our hills later in the week, which will mean
more widespread critical fire weather conditions in the SF Bay
Area hills starting Wednesday Night and continuing at times
through the upcoming weekend and into early next week.

&&

.AVIATION...as of 10:20 PM PDT Monday...For the 06z TAFs. The
marine layer remains at about 1,000 ft AGL around Fort Ord and has
compressed down to a few hundred feet up north at Bodega Bay.
Stratus along the coast has thinned since late this afternoon and
is now mainly confined to the Monterey Bay and down the Salinas
Valley. VFR conditions north of the Monterey area through the
period with IFR/LIFR/VLIFR at KMRY and KSNS due to low clouds
and/or fog through early to mid tomorrow morning. Weak offshore
flow aloft will take over through the next several days and
suppress the marine layer and bring predominately VFR conditions
in the medium term. Winds have begun to ease for the evening and
should remain light overnight.

Vicinity of KSFO...VFR. Patchy FEW to SCT low clouds possible late
tonight. Winds to continue to diminish overnight before breezy
onshore winds return tomorrow afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VLIFR-IFR conditions tonight and
continuing into early to mid tomorrow morning due to low clouds
and potential fog. Satellite currently shows some stratus thinning
over KMRY, but expecting low clouds and/or fog to settle in again
tonight.

&&

.FIRE WEATHER...As of 1:31 PM PDT Monday...Red Flag Warning for
the North Bay above 1000 feet from 11 pm Monday through 8 am Weds.
Initial surge of moderately strong northeast winds looks to peak
in the pre-dawn hours of Tuesday through mid-morning. The
strongest winds will be focused over the Napa hills and higher
terrain of eastern Sonoma county. Winds look marginal for this
event overall with gusts 25-40 mph for wind favored locations.
Overall a low to moderate Red Flag event for this initial event.
Fuels are at or near record dry so any ignitions will remain
problematic as noted by the new Coleman Fire on the Los Padres
Forest which is being managed by the Type 2 team currently
handling the nearby Dolan Fire.

Winds on Tuesday night into early Weds are trending weaker but
will let Red Flags fly given the very dry fuels and coordination
that has occurred with land management agencies and surrounding
WFO's.

There is a distinct lull in winds for the daylight hours of Weds
and right now no fire weather headlines are in effect for that
time frame.

A fresh round of Fire Weather Watches is now in effect from late
Weds night through Friday morning. This round of Watches includes
the North and East Bay mtns as well as the Santa Cruz mtns. The
Watch for the Santa Cruz mtns is slightly delayed, starting at
1 am Thursday morning. This second event looks much stronger than
tonights event. Latest nam solutions shows widespread 30-45 kt
wind barbs at 925 mb overspreading all hills from Napa southward
to the ridge lines of the Santa Cruz mtns including the East Bay
hills. RH recovery will be non-existent with perhaps even some
drying at night over the North Bay with humidity in the 15-30%
range.

Long range estimate shows another lull in the winds later Friday
into Saturday. However, potential for an even stronger wind event
later in the weekend into early next week as a cold trough dives
in the Great Basin. Climatology often brings our strongest wind
events late in October (think Tunnel and Kincade Fires) as we get
more cold air intrusions into the Great Basin. Will be an active
fire weather week with national fire fighting resources working
large fires in CA, CO, NM and Arizona.

&&

.MARINE...As of 8:26 PM PDT Monday...Northwest winds will
continue tonight with locally stronger winds over the northern
outer waters. Winds will increase across the waters beginning
tomorrow evening, particularly over the northern outer waters
where a gale watch is in effect from tomorrow evening through
Wednesday evening. These winds will generate steep fresh swell
resulting in hazardous seas conditions. Stronger winds will then
expand across much of the rest of the waters mid- week. Mixed seas
will persist with a moderate northwest swell and longer period
southerly swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Red Flag Warning...CAZ507
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

PUBLIC FORECAST: Dykema
AVIATION: AS
MARINE: AS
FIRE WEATHER: RWW

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