655 
FXUS66 KMTR 170758
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1258 AM PDT Fri Oct 17 2025

...New SHORT TERM, LONG TERM, BEACHES...

.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...
(Tonight through next Wednesday)
Issued at 918 PM PDT Thu Oct 16 2025

Moderate northwesterly breezes will continue through the end of
this week. A few gusts will be strong, favoring the outer waters
and south of Pigeon Point for the inner waters. A longer period
northwesterly swell arrives this weekend 7 to 10 feet at 15
seconds.

&&

.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...Canepa

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