711
FXUS66 KMTR 170953
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
253 AM PDT Fri Oct 17 2025

...New MARINE...

.KEY MESSAGES...
Updated at 1249 AM PDT Fri Oct 17 2025

 - Warming and drying trend through Saturday with some offshore
   winds in the higher elevations

 - Long period northwesterly swell will bring an increased risk of
   sneaker waves and rip currents to Pacific Coast beaches Friday
   night and into Saturday

 - Slightly cooler conditions next week

&&

.SHORT TERM...
Issued at 1249 AM PDT Fri Oct 17 2025
(Today and tonight)

Satellite imagery shows generally clear conditions across the region
with patches of stratus, notably a couple of patches from the
southwestern corner of San Francisco down through the coast of San
Mateo County. There`s a slight chance (around 10-20% probability) of
fog developing in the North Bay through the morning, but it is a low
confidence forecast and offshore flow aloft and at the higher
elevations may disrupt the marine layer. The clear skies should
allow for robust radiational cooling through the nighttime, with
lows dropping into the middle 40s to lower 50s in the lower
elevations, with the higher elevations of the North bay edging into
the middle 50s and parts of the interior Monterey and San Benito
counties seeing lows into the lower 40s or the upper 30s. Any low
clouds that do develop should mix out by the late morning hours. As
a side note, while we would usually associate offshore wind flow
with fire weather threats, the fact that these offshore winds are
relatively light along with the recent rainfall should put a damper
on the risk for the next couple of days.

The weather pattern is dominated by the interaction between a
positively tilted trough, with the parent low pressure system moving
across the Dakotas and extending into and off of southern
California, and a ridge over the central Pacific that extends into
the Pacific Northwest. The interaction results in northerly flow
aloft, helping to reinforce a warming and drying trend across the
region. Through the day, the trough is expected to "split", with one
piece getting dragged to the east into the Desert Southwest while a
cut off low develops off the coast of Baja California. This should
allow the influence of the ridge to strengthen and expand over more
of the West Coast, allowing for warmer temperatures today. Highs
across the region range from the middle to upper 70s across the
inland valleys, to the lower to middle 70s along the Bays and the
middle to upper 60s along the Pacific coast, generally near or
slightly below the seasonal average.

&&

.LONG TERM...
Issued at 1249 AM PDT Fri Oct 17 2025
(Saturday through Thursday)

The warming trend continues through the upcoming weekend, with parts
of the inland valleys reaching the lower to middle 80s, with even
the passing of an upper level trough through British Colombia and
the Pacific Northwest doing little to cause a sensible drop in
temperatures. Offshore flow could develop on Monday and Tuesday, as
the cutoff low meanders closer to southern California and leave
behind slightly cooler temperatures through Thursday.

Next Friday and the following weekend see the return of rain chances
across the region as a deep trough develops in the Gulf of Alaska
and approaches the West Coast. As of the latest update, the CPC has
put out a moderate risk (40-60% probability) of heavy precipitation
across the North Bay from the 24th to the 27th. Ensemble model
clusters show substantial differences in sensible weather outlooks
between differing solutions regarding the strength and timing of the
incoming trough. Any discussion of rainfall totals thus falls into
the head-in-the-clouds fantasy land where any model output should be
considered highly fallible at best. Stay tuned...

&&

.AVIATION...
(06Z TAFS)
Issued at 921 PM PDT Thu Oct 16 2025

VFR is forecast through the evening except for patchy low clouds
/MVFR-IFR/ developing along the immediate coastline. The evening
00z Oakland upper air sounding shows a precipitable water of 0.54"
(25th percentile for the time of year) with a good radiative
cooling window open i.e. drier layer above the boundary layer for
nocturnal longwave radiative cooling to space. A loss of heat to
space will cool temperatures near surface dewpoint temps (measure
of water vapor) tonight and Friday morning with a few areas of fog
including dense fog probable (20-50%, greater than 50% over the
SF Bay early Friday morning). ECMWF and GFS show cirrus clouds
arriving from the north tonight and Friday, which may slow
radiative cooling a little overnight. Diurnal surface heating and
mixing results in VFR redeveloping Friday.

Vicinity of SFO...VFR continues through the evening. Radiative
cooling will result in low clouds and mist/fog /IFR/ 11z-15z
Friday with IFR prevailing until 18z Friday. VFR thereafter for
Friday. West-northwest wind 10 to 15 knots, decreasing and
becoming light and variable to light easterly Friday morning to
mid afternoon. West wind near 10 knots redevelops by late Friday
afternoon or early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR however SCT-BKN low clouds /MVFR-IFR/
will form nearby the terminals during the evening, with increasing
probability of LIFR-IFR in fog and low clouds late tonight and
early Friday morning. Light east to southeasterly winds tonight
increasing to 5 to 10 knots perhaps up to 15 knots in the Salinas
Valley late tonight and Friday morning; cool air drainage winds
will help to mix out the fog /LIFR-IFR/ earlier than usual Friday
morning. By late afternoon winds shift to onshore 5 to 10 knots.

&&

.MARINE...
(Today through Wednesday)
Issued at 253 AM PDT Fri Oct 17 2025

Moderate northerly breezes will continue through the end of this
week. Today, fresh to strong gusts will are expected for the
northern most outer waters, perhaps lingering into Saturday
morning. A longer period northwesterly swell arrives this weekend
7 to 10 feet at 15 seconds. Northerly winds should become fresh to
strong late Sunday into Monday, with near gale force gusts
expected for the outer waters north of Point Pinos.

&&

.BEACHES...
Issued at 1249 AM PDT Fri Oct 17 2025

A long-period northwesterly swell with periods of around 15 to 17
seconds is approaching the coast through the day and will begin
impacting the coastal waters tonight. The long-period swell
increases the risk of sneaker waves and rip currents across the
Pacific coast, potentially catching unaware swimmers off-guard.
Never turn your back to the ocean! Swim near a lifeguard if
possible! If caught in a rip current, swim parallel to shore until
you escape its influence.

DialH

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from this evening through Saturday
     evening for CAZ006-505-509-529-530.

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

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Canepa
MARINE...KR

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