012
FXUS66 KMTR 101740
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
940 AM PST Fri Jan 10 2025

...New AVIATION...

.SYNOPSIS...
Issued at 1233 AM PST Fri Jan 10 2025

Another beautiful day Friday! Strong offshore winds return to the
higher elevations early Saturday through Sunday morning, with
another push early Monday through Tuesday. The overall pattern
will keep mostly clear skies and unseasonably dry weather around
through the week.

&&

.UPDATE...
Issued at 906 AM PST Fri Jan 10 2025

No changes to the forecast this morning. Some high clouds may
sneak across the North Bay counties, otherwise look for mostly
sunny skies. Highs will be quite variable today depending on your
location. Temperatures range from the mid to upper 50s for higher
elevation mountains and for those right along along the coast
whereas the 60s will be found elsewhere. Some valley locations of
the South Bay and Central Coast may approach 70.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1233 AM PST Fri Jan 10 2025

We are keeping a close eye on a push of strong winds overnight,
but so far anything over 30 mph is mostly confined to the highest
peaks in the North and East Bay. As such, no wind advisory is
needed. The SFO-WMC gradient peaked around -14.5 mb around 8 PM
Thursday, and has since relaxed to -10.5 mb. This trend will
continue as the ridge axis becomes centered over the Bay Area and
extends to the NE, leading to a gentle breeze Friday. With clear
skies, abundant sunshine, and afternoon temperatures about 5
degrees above normal, Friday will be a spectacular day across the
Bay Area and Central Coast, although some haze may get trapped
under the strong high pressure. By Friday night, the next
disturbance in the 500 mb pattern will begin sliding down from the
Pacific Northwest towards the Rocky Mountains. At the surface, a
back-door cold front will form, with cold air taking hold across
the intermountain west. This will tighten the gradient with the
subtropical high pressure offshore, refreshing the strong N-NE
winds by early Saturday morning.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 1233 AM PST Fri Jan 10 2025

By Saturday morning, the leading edge of the back-door cold front
will extend somewhere along the Sierra or Central Valley. The
current prognostic charts from the Weather Prediction Center
supports 850 mb temperature anomaly guidance that this front will
push to the coast and beyond through the day Saturday. Unlike our
typical cold fronts that bring maritime moisture, this inland
front will only bring another round of strong offshore winds and
colder temperatures. More than likely, there won`t be any clouds
associated with this frontal passage, much less any rain. I
leaned heavily on the local WRF for winds and gusts in the
official forecast, mainly since it preformed so well with
Tuesday`s offshore event. A wind advisory is in effect from
midnight Friday night through 10 AM Sunday for most of the higher
elevations across the Bay Area, where gusts are expected to reach
up to 50 mph. The 850 mb temperature is currently around 16C and
will steadily fall to around 7C by Saturday morning. That`s a
drop from around the 99th percentile to the daily mean for this
time of year, and will bring a return of more seasonable
temperatures.

The next feature of interest moves through Sunday. A pair of short
wave troughs are expected to move through the Bay Area, and will
likely combine forces to spawn a cut-off low pressure system off
the coast of Southern California. While this sounds similar the
the cut-off low earlier this week, the position is farther west,
and may support an unusual E or even SE upper level synoptic wind
direction across the region. Once it becomes cut-off on Monday or
early Tuesday, this system will remain in place through the
majority of the work week without any upper level support to pick
it up. The strongest winds look to be Monday before the low
gradually weakens. The NBM doesn`t currently trigger any wind
advisory criteria, but it may not handle this situation well due
to the bias correction fighting the unusual set-up. We will have
to wait another day or two to start seeing more high resolution
solutions to this problem before making that determination.

In summary, we will have a couple more pushes of strong offshore
winds and temperatures will retreat to normal. Otherwise, this
unusual dry stretch will continue. We`re in the middle of the
rainy season, and the ECMWF and GFS ensemble members all show a 0%
chance of rain through the 16th, with less than 10% through the
20th. Roughly 1/2 of the members are dry through the 25th and
there is no indication of significant rainfall after that. It`s
still early, but there`s a good chance this will go down as the
driest January in the last decade. Downtown San Francisco has
0.19" so far this month, and would need to beat 0.61" from 2022 to
avoid this benchmark. Normal January rainfall is 4.38 inches.

&&

.AVIATION...
(18Z TAFS)
Issued at 939 AM PST Fri Jan 10 2025

VFR through the first half of the TAF period with increasing
confidence for lowering ceilings into Saturday morning as a frontal
boundary approaches and passes through the region. LIFR/IFR ceilings
and reductions in visibility will impact many coastal areas with
scattered clouds inland, but will be quick to clear early Saturday
as more moderate to breezy north winds arrive by Saturday afternoon.

Vicinity of SFO...Winds become westerly into the afternoon and
northwesterly Friday night. As the frontal boundary approaches late
in the night, expecting scattered low level clouds to develop (brief
MVFR/IFR). These clouds will be quick to clear by midmorning
Saturday as winds increase out of a northerly direction.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Expect light to moderate southeasterly
drainage winds to affect the terminals through late morning, with
lighter and more variable winds expected in the afternoon. LIFR/IFR
ceilings to affect the terminals into the late night and clearing by
about 17Z Saturday.

&&

.MARINE...
(Today through Wednesday)
Issued at 906 AM PST Fri Jan 10 2025

Stronger and gustier northerly winds build into the day on Friday
with elevated wave heights between 10 to 15 feet developing Friday
night. The strongest winds will be located over the  northern
outer waters where gale force gusts are likely over the  weekend.
Seas reamin elevated into the work week, but winds look  to
reduce.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from midnight tonight to 10 AM PST Sunday for
     CAZ504-512-514-515.

PZ...Gale Warning from 3 AM Saturday to 3 AM PST Sunday for SF Bay N
     of Bay Bridge.

     Small Craft Advisory from 3 AM Saturday to 3 AM PST Sunday for
     Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt
     Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PST Sunday
     for Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 9 PM PST this
     evening for Pt Arena to Pt Reyes 10-60 NM.

     Gale Warning from 9 PM this evening to 3 AM PST Sunday for Pt
     Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 PM this evening to 3 AM PST Sunday
     for Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...RGass
MARINE...RGass

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