AFOS product AFDMTR
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Product Timestamp: 2025-10-19 04:52 UTC

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268 
FXUS66 KMTR 190452
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
952 PM PDT Sat Oct 18 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 218 PM PDT Sat Oct 18 2025

 - Warmer and drier weather with light offshore winds in the 
   higher elevations into early next week

 - A Beach Hazards Statement remains in effect through 11PM
   tonight for increased risk of sneaker waves and rip currents
   along the Pacific Coast beaches

 - Slightly cooler conditions begin midweek with unsettled weather
   to return next Friday into the following weekend

&&

.UPDATE...
Issued at 927 PM PDT Sat Oct 18 2025

The forecast was updated to include coastal fog for tonight and 
Sunday morning. Microphysics satellite imagery shows areas of fog
and very low clouds over the coastal waters. The southern coastal
waters fog and very low clouds are converging with fog caught up 
in a southerly wind reversal along the Monterey County coastline. 
At 9 pm the SMX-SFO pressure gradient was 1.2 mb, however the SFO-SBA
gradient was northerly at 0.7 mb. Fog within the shallow marine
layer will result in surface visibilities at or below 1/2 mile, 
including dense fog at less than 1/4 mile visibility. Fog will 
enter in the Salinas Valley, while also moving northward along the
coastline tonight and Sunday morning. The High Resolution Rapid 
Refresh (HRRR) model is showing some of the pressure gradient from
SMX to SFO tonight, but shows the gradient reversing Sunday. 
Similarly the NAM model is showing a weak northerly pressure 
gradient Sunday. Tough to say at this point if the current 
southerly wind reversal is, at the synoptic scale, connected to 
the upper low (its surface ridge) ~ 700 miles south-southwest of 
Monterey or independent from the upper low and due to smaller 
scale ridging on the Central Coast or if both are influencing the 
surface gradient; not all the time, but model forecasts are 
sometimes late forecasting the onset of SMX-SFO, SBA-SFO i.e. 
southerly pressure gradients. 

On the subject of complex short term weather, at one point during
the late afternoon across a 5 mile span from KMRY Airport to Pebble
Beach/Carmel we had a large (20F) dewpoint temperature difference,
upper 30s at KMRY, upper 50s Pebble Beach/Carmel while there was 10F
air temp difference. Similar elevations had very different water vapor
differences over a short distance, both typically evenly maritime
influenced. The dryness (dewpoint temps upper 30s) was real at KMRY,
stepping outside to observe the weather earlier you could feel the
distinct dryness in the air. Interesting to attain a difference like
that given the relative weakness of the SMX-SFO gradient and air temps
just above sea level in the lower level temperature inversion (lower
70s). 

The 00z October 19th GFS is coming in and showing similar output 
to previous global output: strong to even stronger zonal 200 mb 
jet stream winds cross the North Pacific reaching the West Coast 
through the week, resulting in an increasing chance of rain here 
in our forecast area later in the upcoming week and weekend. 
Instability and low pressure /wave/ development accompanies strong
wind shear in the jet stream, pulling in a fair amount of water 
vapor for rain development including in our forecast area late 
next week and weekend. The northern hemispheric pattern remains 
winter-like, very energetic with a number of long wave troughs.
We've had quite a strong (early) start to our rain season and 
water year with two months to go to reaching the winter solstice.

For additional information on the forecast please see the previous
discussions.

&&

.SHORT TERM...
Issued at 218 PM PDT Sat Oct 18 2025
(This evening through Sunday)

High pressure and ridging have settled back in over the Bay Area and 
Central Coast and helped to warm temperatures up today with a cut-
off low located to our southwest offshore of Southern California. 
Warmer temperatures will continue again on Sunday with highs in the 
mid 70s to low 80s across the interior and in the 60s to low 70s 
along the coastline. Morning low temperatures are forecasted to be 
in the low to mid 50s for the Bay Area and Central Coast, excluding 
the far interior Central Coast where low temperatures will be in the 
40s. Now the caveat to this forecast ties into our next point, light 
offshore winds continue Saturday night into Sunday. Offshore winds 
typically bring in drier air which can reduce cloud cover and 
mitigate fog development. As a result, fog is not anticipated to 
develop tonight. The lack of cloud cover, however, may have an 
additional side effect on our forecast, specifically on the forecast 
accuracy of our low temperatures. This morning the Santa Rosa 
Airport was forecast to reach a low of 50 degrees Fahrenheit. It 
actually reached a low temperature of 45 degrees Fahrenheit thanks 
to increased radiational cooling caused by the lack of cloud cover. 
This phenomena was observed in the interior Central Coast was well 
where some of the highest ridgetops saw low temperatures in the 
upper 30s to low 40s this morning (forecasted to be in the mid to 
upper 40s). It is possible that, given the lack of fog and lack of 
cloud cover forecasted overnight, we may see additional radiational 
cooling tonight with temperatures dropping lower than what is 
currently in the forecast. This would most likely impact the North 
Bay Valleys and portions of the interior Central Coast. Otherwise, 
an overall pleasant weekend continues with the potential for 
unsettled weather to return late next week.

A Beach Hazards Statement remains in 
effect through 11PM tonight due to an increased risk for sneaker 
waves and rip currents. Further information can found in the Beaches 
section below.

&&

.LONG TERM...
Issued at 218 PM PDT Sat Oct 18 2025
(Sunday night through next Friday)

Upper level ridging and high pressure continue into early next week, 
keeping the forecast relatively stable through Tuesday. High 
temperatures will be in the 70s to low 80s across the interior and 
60s to low 70s along the coastline. Offshore winds briefly 
strengthen across the higher elevations of the North Bay Interior 
Mountains Sunday night into Monday morning. This will result in 
locally drier conditions during the day on Monday and overnight 
Monday into Tuesday across the elevated terrain. Fire weather 
concerns remain low given recent wetting rains and moist fuels 
across the region. The pattern begins to change Tuesday as the cut-
off low offshore of Southern California merges with an upper level 
trough and moves into California late Tuesday into Wednesday. This 
is a dry system so we aren't expecting any rain from it, but, it 
will bring noticeably cooler temperatures beginning Wednesday. High 
temperatures across the interior will drop into the 60s to low 70s 
and stay in the 60s along the coastline. Overnight lows will cool as 
well with low temperatures in the mid 40s to mid 50s expected. 

Now for the interesting portion of the forecast: unsettled weather 
looks to return Friday and remains unsettled into the weekend. Model 
guidance continues to indicate a potentially significant atmospheric 
river moving into the West Coast October 25th-27th. Confidence is 
increasing that we will see rain across the Bay Area and Central 
Coast with potentially heavy rain across portions of the North Bay 
starting late Thursday into Friday. The CPC maintains a moderate 
risk of heavy precipitation and high winds over the North Bay and a 
slight risk of heavy precipitation and high winds over the rest of 
the Bay Area and Central Coast through the remainder of the weekend 
(Saturday and Sunday). Given that this system is just under a week 
out, it is still to early to discuss any forecast QPF totals or the 
precise timing of this system as models are still coming into 
consensus. Given the pleasant weather expected this weekend into 
next week, now would be a good time to make sure gutters are cleared 
out and any outdoors objects are secured ahead of this system.

&&

.AVIATION...
(06Z TAFS)
Issued at 951 PM PDT Sat Oct 18 2025

LIFR CIGS are building along the coast, affecting the Monterey Bay 
terminals and approaching HAF later into the night. Winds become 
light overnight with LIFR and IFR CIGS forming at OAK and STS into 
early Sunday. MRY and STS look to be affected by patches of fog and 
mist, leading to poorer visibilities. CIGs clear and and 
visibilities improve into the late morning for most, with HAF 
scattering in the mid afternoon. Winds increase becoming more 
moderate for Sunday afternoon with only a few more breezy areas 
along the coast. Winds become light again into Sunday evening as 
low CIGs form around the Monterey Bay.

Vicinity of SFO...VFR through the TAF period. Light west winds last 
into the early morning on Sunday before becoming lighter and more 
variable as low clouds form near the terminal. These clouds erode 
into the late morning as west winds return. These winds increase 
into the afternoon, becoming moderate through the evening, but 
become light and variable again into Sunday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Cloud cover is filling around the bay with 
LIFR CIGs at the terminals. Expect some reductions in visibilities 
with these CIGs and further reductions at MRY into early Sunday. 
CIGs erode into the late morning as moderate winds return. Winds 
reduce again into Sunday night with low CIGs returning.

&&

.MARINE...
(Tonight through next Friday)
Issued at 951 PM PDT Sat Oct 18 2025

A moderate NW breeze and a moderate-rough NW swell will continue
across the coastal waters today. Stronger winds will arrive
Sunday, although the swell will gradually abate. By Sunday night,
a new NW swell will move in, combining with the wind waves to
build very rough conditions across the exposed coastal waters.

&&

.BEACHES...
Issued at 106 AM PDT Sat Oct 18 2025

A Beach Hazards Statement is in effect through 11 PM tonight as a 
long-period swell impacts the Pacific coast. The San Francisco and 
Point Arena buoys have begun reporting swell periods of 19 seconds. 
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. 

Beyond the expiration of the Beach Hazards Statement, another long 
period swell arrives in the early part of next week with a Beach 
Hazards Statement or a High Surf Advisory possible depending on how 
the forecast evolves.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement until 11 PM PDT this evening for CAZ006-
     505-509-529-530.

PZ...Small Craft Advisory from 9 AM Sunday to 9 AM PDT Monday for Pt 
     Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM Sunday to 9 AM PDT Monday for Pt 
     Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from 9 AM Sunday to 3 PM PDT Monday for Pt 
     Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 3 PM Sunday to 3 PM PDT Monday for 
     Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Murdock
MARINE...Murdock

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