Strong Wind in California, November 2 to 5, 2024

Area Forecast Discussion
National Weather Service San Francisco CA
1044 PM PDT Sat Nov 2 2024

...New AVIATION...

.SYNOPSIS...
Issued at 115 PM PDT Sat Nov 2 2024

Beneficial rainfall overnight last night, though fire weather
concerns remain elevated through the upcoming week with strong
offshore winds and dry conditions expected.

&&

.UPDATE...
Issued at 837 PM PDT Sat Nov 2 2024

The region remains generally dry with some stratus developing at
the higher elevations. A weak front of the coast of far northern
California might bring a sprinkle or two to the northwestern
corner of Sonoma County overnight, but not expecting anything
close to the rainfall totals from last night. Maybe a few
hundredths of drizzle at best. The forecast remains on track, with
the main concern still the push of offshore winds Sunday into
Monday morning, and how that push impacts how dry the fuels will
be heading into the second push of offshore winds midweek.

In addition, the arrival of long period northwest swell to our
waters tomorrow increases the risk of sneaker waves and rip
currents, with a Beach Hazards Statement out for most of the
coastline (except northern Monterey Bay, which remains sheltered
from the swell impacts) Sunday afternoon through Monday evening.

DialH

&&

.SHORT TERM...
(This evening through Monday)
Issued at 115 PM PDT Sat Nov 2 2024

Shower activity ending across the region today with only a few light
showers lingering over southern portions of the interior Central
Coast. Visible satellite showing a fairly uniform cumulus field
roughly from the delta southward out in front of an area of
mesoscale subsidence centered around the northern CA coast. Modest
instability around 200 J/Kg and steep lapse rates around the
altitude of our higher terrain allowing these Cu to persist through
peak heating this afternoon, but strong stability aloft is keeping a
lid on things and will keep any vertical development rather shallow.
As such, we are not expecting any more rain for today outside of a
very slight chance for brief sprinkles in the higher terrain from
the Santa Cruz mountains southward.

The tables turn Sunday as the upper low deepens further in the
southwest US and surface high pressure builds in its wake across the
Great Basin. First and foremost, will mention that the rain
overnight was certainly beneficial as many locations outside of the
rain shadows ended up with at or slightly above what was forecasted.
This is generally good news in the short term, but rapid drying and
elevated fire weather conditions are still expected to some extent
(will discuss the implications for the mid-week event in the LONG
TERM). There has not been much change in the overall forecast
magnitude of the offshore winds Sunday into Monday morning. Latest
guidance is still holding the offshore-oriented pressure gradients
steady with recent model simulations over the past 24-36 hours. This
is providing reasonably high confidence in this event through
Monday. As of this forecast, it appears that winds will begin to
increase Sunday through the day with a relative peak early Monday
morning. Still thinking that the strongest winds will be in the
higher terrain of the Diablo Range, Vaca Mountains, and the Santa
Lucia Highlands with gusts up to 45-50 mph. Once again, the good
news is the level of moisture retention in the air and fuels.
Starting the day Sunday with very good overnight RH recovery gives
us a decent leg up, with afternoon minimum RH expected to drop
into the 25-40% range. This forecast update and the recent
rainfall have prompted the decision to NOT issue any fire weather
hazards for Sunday/Monday as of this issuance. However, fire
weather conditions are still elevated - but not critical - due to
dry conditions and strong offshore winds. Winds are expected to
decrease through Monday morning with concerns lessening by the
evening hours.

&&

.LONG TERM...
(Tuesday through next Friday)
Issued at 115 PM PDT Sat Nov 2 2024

Quite a bit of concern over the mid-week system, partially due to
the evolution of the upper low and its uncertainty. Guidance is
advertising a Rex block pattern in which the upper low over the
Desert SW becomes very positively tilted and partially "blocked" by
an upper ridge to its north (over the PNW). The problem with making
deterministic judgments on this system as of now is that it is a
slow moving feature and comes with a rather large amount of
uncertainty. The aforementioned offshore-oriented pressure
gradients show much less agreement Tuesday night going through
Wednesday. In fact, the model spread is a difference of about 5-6
mb, which can be a rather meaningful difference in terms of the
strength of the wind and its drying potential. As it stands,
expect another period of elevated fire weather conditions late
Tuesday through at least Wednesday afternoon. By this point, any
rain that has fallen this weekend will have had ample time to
mostly dry out of the live fuels and show little benefit given the
precursor offshore wind event Sunday/Monday. This is very much a
"wait and see" scenario in that we will observe how fuels have
responded to the early week offshore event and allow guidance to
come to a better consensus before conveying any increase in
confidence. This does have the potential to be a significant
event, but again, we wait and see. I suspect we will have a much
better idea by Monday once models have a better grasp on the exit
of the current trough and the evolution of the pattern as a whole.

&&

.AVIATION...
(06Z TAFS)
Issued at 1029 PM PDT Sat Nov 2 2024

VFR conditions expected through the TAF periods. A weak cold
front will move through overnight, helping to keep the atmosphere
well mixed and skies clear. This system will also bring abnormally
strong winds through the night.

Vicinity of SFO...VFR conditions continue through at least
midnight. While the TAF stays VFR, there is a 15% chance for and
MVFR or IFR ceiling early Sunday morning. Strong onshore winds
will continue through the night and shift more northerly while
strengthening by mid-day.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...30% chance for an MVFR ceiling early
Sunday morning. Otherwise VFR conditions with moderate to strong
NW winds will persist through the TAF period.

&&

.MARINE...
(Tonight through next Friday)
Issued at 837 PM PDT Sat Nov 2 2024

Surface high pressure builds in behind the cold front resulting
in strengthening northwest winds with gale-force gusts developing
this evening. These winds will generate very rough wind waves.
Long period northwest swell arrives Sunday night and Monday,
further  building the significant wave heights.

&&

.FIRE WEATHER...
Issued at 115 PM PDT Sat Nov 2 2024

Slightly better outlook this morning for the first of two offshore
winds events progged for this upcoming week. Most areas received
beneficial rainfall overnight that will dampen fire weather
concerns slightly going into Sunday. However, vigilance is still
encouraged as we are early in the season and live fuels have not
accumulated much moisture thus far, so any potential benefit from
last night could be erased relatively easily as the offshore winds
continue into Monday morning. Current live fuel moisture forecast
still advertises ERCs around or above the 60th percentile by midweek.
Therefore, while the early week offshore event holds a slightly
more positive outlook, the midweek system could be more
concerning. By that time, live fuels would have had plenty of time
to dry out sufficiently, and there is considerable uncertainty
regarding the evolution of the pattern during the peak wind period
Wednesday. The RH forecast for Tuesday-Thursday will potentially
need to be nudged lower after losing some evapotranspiration
potential to the offshore winds earlier in the week that I suspect
some models may be holding on to. Will need to wait and see how
fuels respond early to the winds through Sunday, and will likely
have a much clearer picture of the midweek system by Monday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from Sunday afternoon through Monday
     evening for CAZ006-505-509-530.

PZ...Small Craft Advisory until 9 PM PDT Sunday for Mry Bay-Pt Arena
     to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N
     of Bay Bridge.

     Gale Warning until 9 PM PDT Sunday for Pigeon Pt to Pt Pinos 0-
     10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Gale Warning until 3 AM PDT Monday for Pt Arena to Pt Reyes 10-
     60 NM.

&&

SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...Flynn
MARINE...Canepa

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