792
FXUS66 KMTR 181155
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
455 AM PDT Fri Oct 18 2024

...New AVIATION...

.SYNOPSIS...
Issued at 133 AM PDT Fri Oct 18 2024

Red Flag conditions continue through Saturday due to an inside
slider weather pattern.

&&

.SHORT TERM...
(Today and Saturday) Issued at 133 AM PDT Fri Oct 18 2024

An inside slider event is well underway as an upper-level trough
digs into the Great Basin. The ramifications of this pattern are
already being observed across the region with relative humidity 50-
70% drier than 24 hours ago and higher elevations recording wind
gusts to 50 mph with Mt. St Helena gusting as high as 75 mph.
Fire weather concerns will only increase throughout this event due
to the compounding effects of the antecedent conditions and a
backdoor cold front ushering in much drier air through the day
today. Winds will veer to become northeasterly/offshore through
the morning as the upper-level trough digs south and becomes a
cutoff low in the Desert Southwest. Winds largely on the order of
25-35 mph can be expected with gusts to 50 mph. Highest terrain,
ridgetops, gaps, and passes will be favored with isolated gusts up
to 65 mph. Every effort should be made to prevent a wildfire
spark always, but especially over the next two days.

&&

.LONG TERM...
(Saturday night through Thursday)
Issued at 133 AM PDT Fri Oct 18 2024

The offshore pressure gradient will weaken and begin to reverse
Saturday night, restoring order and onshore flow to the region. The
return of onshore flow will help moderate temperatures, reestablish
the marine layer, and ease fire weather concerns going into next
week. The start of next week looks to be relatively quiet with a
stable zonal flow pattern dominating the Contiguous United States.

&&

.AVIATION...
(12Z TAFS)
Issued at 440 AM PDT Fri Oct 18 2024

Guaranteed VFR conditions today as dry offshore winds keep any
chance of clouds at bay. The SFO-WMC gradient is continuing to
build, currently at -4.5 mb. Surface winds will remain moderate to
strong today, before decreasing to a gentle breeze this evening.
The direction will also shift to onshore this afternoon as the
synoptic forcing weakens and the sea breeze kicks in. Low level
wind shear has been removed from the TAFs. There were several
reports of moderate turbulence overnight, but no specific PIREP
for LLWS, and, while the boundary layer will decouple overnight,
the the wind shear isn`t expected to be as strong.

Vicinity of SFO...Very dry air has moved in, and the dew point is
currently -2C at OAK. This will keep the skies clear all day.
Winds are starting the morning moderate-strong from the NNW, but
will gradually back to a more standard NW direction through the
day. The wind speed will increase a bit in the afternoon, but then
diminish to a gentle breeze this evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the TAF period. Winds will
shift following the typical diurnal pattern and should remain
moderate all day.

&&

.MARINE...
(Today through Wednesday)
Issued at 439 AM PDT Fri Oct 18 2024

The gradient between subtropical high pressure in the Eastern
Pacific and a weakening back-door cold front along the coast is
supporting a strong N breeze and 10-12 ft seas across the coastal
waters. Buoys are reporting the earlier gale force gusts have
diminished. Strong winds will continue through the day,
increasing briefly to near gale force in the NW zones this
afternoon. Otherwise, conditions will continue to improve through
the weekend with winds decreasing to a moderate NW breeze and wave
heights abating to 5-7 ft by Sunday. Similar conditions are
expected to persist through the week. Guidance is starting to hint
that another cold front may approach the coast next weekend.

&&

.FIRE WEATHER...
Issued at 439 AM PDT Fri Oct 18 2024

Red Flag conditions arrived Thursday evening with overnight relative
humidity dropping into the mid 20% range through the North Bay and
East Bay Mountains and several weather stations reporting wind gusts
as high as 50 mph, Mt. St. Helena recorded the strongest gust at 75
mph. This afternoon through Saturday morning will be the most
critical period before the winds start to decrease. A Red Flag
Warning is in effect through 5 PM Saturday for the Bay Area and
Central Coast with the exception of coastal Marin, Monterey, and
Sonoma Counties. Sustained northeasterly winds largely on the order
of 25-35 mph can be expected with gusts to 50 mph, and isolated
gusts to 65 mph across the highest terrain and ridgetops and through
gaps and passes. The windiest timeframes will be through Friday
morning and Friday night through Saturday morning. Poor relative
humidity as low as 10% with no overnight relief is expected in the
higher elevations. While fuels are near average for this time of
year, they will noticeably respond while remaining below record
territory.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 5 PM PDT Saturday for CAZ006-502>504-506-
     508>510-512>518-528-529.

     Wind Advisory until 8 AM PDT Saturday for CAZ504.

     Wind Advisory until 11 PM PDT this evening for CAZ510-514-515.

PZ...Small Craft Advisory until 3 AM PDT Saturday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay
     Bridge.

     Small Craft Advisory until 9 PM PDT this evening for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
     to Pt Reyes 10-60 NM.

     Gale Warning from 3 PM this afternoon to 3 AM PDT Saturday for
     Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory until 9 AM PDT Saturday for Pigeon Pt to Pt
     Pinos 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Flynn
MARINE...Flynn

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