972
FXUS66 KMTR 101001
AFDMTR

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

...New SYNOPSIS, SHORT TERM, LONG TERM...

.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.

&&

.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...
(06Z TAFS)
Issued at 845 PM PST Thu Jan 9 2025

VFR is expected to prevail through the TAF period. There is a
slight chance of fog at STS, but confidence is too low for
mentioning in the TAF. Mostly light to moderate offshore flow
through the day tomorrow with a return of weak onshore flow,
especially along the coast, Friday evening.

Vicinity of SFO...VFR. Light and variable winds are expected
through the TAF period, with a return of weak onshore flow Friday
by Friday evening.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals...VFR. Light to moderate SE winds will
persist into the early morning hours Friday, then become light and
variable in the afternoon.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 845 PM PST Thu Jan 9 2025

Light to moderate offshore winds continue across the bays and
coastal waters tonight before a weak cold front moves through the
region on Friday. Upper level ridging will then rebuild over the
weekend and see a return of conditions hazardous to small crafts
across the outer waters. Gusty, near gale force, northerly to
northeasterly winds and elevated wave heights between 10 to 15
feet will develop late Friday and continue into early next week.
The strongest winds will be located over the far northern outer
waters where gale force gusts are likely Saturday into Sunday.

&&

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

PZ...Small Craft Advisory from 3 PM this afternoon to 3 AM PST
     Saturday for Pt Arena to Pt Reyes 10-60 NM.

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

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...JM
MARINE...DialH

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