298
FXUS66 KMTR 280409
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
909 PM PDT Sun Jul 27 2025

...New UPDATE, MARINE...

.KEY MESSAGES...
Updated at 150 PM PDT Sun Jul 27 2025

 - Temperatures warm slightly but remain below seasonal averages
   this week.

 - Strong onshore afternoon winds will gradually increase through
   mid-week.

&&

.UPDATE...
Issued at 902 PM PDT Sun Jul 27 2025

No changes are needed to the forecast this evening. Stratus is
slowly filling into interior valleys and will continue to do so
into the overnight and early morning hours.

&&

.SHORT TERM...
Issued at 150 PM PDT Sun Jul 27 2025
(This evening through Monday)

Below normal temperatures continue within the marine layer while
seasonal to slightly below normal continue across the higher
elevations above the marine layer. Persistent upper level troughing
continues over the West Coast with the 12Z sounding showing the
marine layer deepening to around 2000 ft overnight. The marine layer
should stay relatively steady around 2000 ft in depth through
tonight, however, stratus coverage and drizzle potential look to be
much patchier tonight than they were this morning. This is due to
the arrival of a relatively drier airmass in the lower and middle
levels of the atmosphere which will help to mix out cloud cover over
portions of the interior. There will be enough lingering moisture to
support patchy low clouds and drizzle overnight but it will mainly
be confined to the coastline and SF Bay Shoreline. Any precipitation
accumulation from tonight`s drizzle is likely to range from a trace
to a few hundredths of an inch.

Temperatures will warm Sunday into Monday with most sites seeing
high temperatures 4-5 degrees higher on Monday than on Sunday as a
drier, warmer airmass moves in above the marine layer. This will
result in highs in the upper 70s to low 90s across the interior and
upper 50s to 60s along the coastline. This warmup is most likely to
be felt across the higher elevations where high temperatures jump
from the low to mid 80s to the upper 80s to low 90s. For areas
within the marine layer, Monday`s high temperatures will still be
running about 4 to 12 degrees below normal while areas above the
marine layer will be closer to seasonal averages. Diurnally breezy
onshore winds are expected Monday afternoon/evening with gusts to
around 25-30 mph across mountain gaps/passes and along the
coastline.

&&

.LONG TERM...
Issued at 150 PM PDT Sun Jul 27 2025
(Monday night through next Saturday)

In the longer term, upper level troughing continues with the marine
layer holding steady around 1500-2000 ft and a warm, dry air mass
located just above the marine layer. Daytime high temperatures will
remain consistent in the upper 70s to low 90s across the interior
and upper 50s to mid 60s along the coastline through the end of the
week. No Sky July looks to continue through at least the end of this
week with stratus most likely along the coastline and along the SF
Bay Shoreline. Drizzle is a little less likely starting Tuesday
morning given the drier airmass but cannot fully rule out patchy
drizzle impacting coastal residents Tuesday and Wednesday morning.
Diurnally breezy onshore winds continue with winds strengthening
across the marine environment starting Tuesday. The SFO-WMC pressure
gradient peaks around +8 to +10 hPa (moderate onshore flow) in the
afternoon/evening Monday and Tuesday with gusts to around 25-30
mph along the coast and in mountain gaps/passes. Across the marine
environment, a low pressure system in the Gulf of Alaska will
push the Pacific High further southward and gradually shift the
center of this high to the East (closer to the West Coast) Tuesday
into Wednesday. This will allow more northerly winds to
strengthen across the marine environment but keep the strongest
marine winds over the outer coastal waters.

Friday, GFS guidance shows weak high pressure building in over
the southernmost portions of our CWA as high pressure over the
Central United States and Four Corners region expands westward.
This is disrupted by weak shortwave troughing on Saturday which
will help cool temperatures down 1-2 degrees. In the longer term,
guidance does suggest high pressure will build into the West Coast
early next week with CPC guidance showing temperatures leaning
above normal. This is still a ways out so we`ll continue to
monitor the overall trends and see if models continue to show this
ridge developing.

Drier and warmer conditions are expected above the marine layer
(~2000 ft) with daytime relative humidity values dropping to between
14-25% across the interior Central Coast. Temperatures are in the
mid to upper 90s across this area with temperatures running about
seasonal to 2-5 degrees above normal for this time of year. Onshore
winds will help to mitigate fire risk and fuels remain moist thanks
to recent troughing and cooler/drizzly weather.

&&

.AVIATION...
(00Z TAFS)
Issued at 611 PM PDT Sun Jul 27 2025

Interior locations remain VFR for the most part, while coastal areas
have either remained socked in or have started to see the return of
stratus. The stratus is expected to return for interior locations
though may not occur until well into the overnight hours or by early
Monday morning. MVFR to IFR cigs are possible, with clearing
occuring by mid to late morning depending on location.

Vicinity of SFO...The question for the immediate near term will be
will be how much does the stratus flirt with the airport. There
could be brief periods of brief VFR over the next hour or with MVFR
cigs then through the evening. IFR cigs return overnight thanks to
the stratus returning. Stratus should begin to erode late morning,
leaving a period of VFR cigs Monday afternoon. The stratus should
return fully earlier Monday evening, bringing another round of IFR
cigs.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus has returned leaving the south half
the Bay with MVFR cigs, and VFR to the north. Eventually stratus
fills completely in and sites will have cigs drop to IFR overnight.
Skies should clear late morning, with another period of VFR
conditions though it will be shorter lived than today. Cigs start to
early in the evening.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 902 PM PDT Sun Jul 27 2025

Moderate to breezy northwest winds will persist for much of the
upcoming week across the waters. Winds will gradually increase
through Monday leading to locally hazardous conditions. Winds will
be locally stronger along the coast, specifically on the the
favored coastal jets such as along Point Reyes, Pigeon Point, and
south of Point Sur.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from noon to 9 PM PDT Monday for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PDT Tuesday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

&&

$$

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

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