FXUS66 KMTR 260417
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
917 PM PDT Sat Apr 25 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 952 AM PDT Sat Apr 25 2026

 - Isolated, light showers through Sunday

 - A warming and drying trend next week

&&

.SHORT TERM...
Issued at 952 AM PDT Sat Apr 25 2026
(This afternoon through Sunday)

An upper level low roughly 200 miles west of the Monterey Bay 
will approach the coast over the next 12 hours. This system is 
bringing widespread overcast skies, some very light rain, and 
cooler temperatures today. Below this upper level disturbance, we 
also have a deep marine layer impacting the surface conditions. 
The 12Z balloon measured the depth at nearly 4,000 feet capped by 
a very strong inversion. Between the moist marine layer and upper 
levels, there is a layer of very dry air between 800 mb and 600 
mb, where the average relative humidity is less than 5%. This dry 
layer will cause much of the rain to evaporate before reaching the
surface today. So far we've recorded 1/100th inch of rain in a 
few different rain gauges throughout the Bay Area and Central 
Coast. Rain will generally fall as light and brief showers, with 
the most activity expected in Santa Cruz and Monterey Counties 
early Sunday morning. All told, we're not expecting to exceed 
1/10th of an inch. For Big Sur Marathon runners, this is the type 
of rain that's nice to run in. The wind will be much weaker than 
normal years, too.

Anytime there is a landfalling low pressure system we need to take a 
look at thunderstorm chances. There are a lot of factors working 
against convection in this environment. The CAPE isn't expected to 
break 100 J/kg, and even that is all below the inversion where the 
air is above freezing. That means there won't be any ice particles 
to create static electricity buildup. Additionally the inversion and 
very dry mid levels are barriers to coherent updrafts. While the NBM 
shows a 5% chance of thunderstorms today, that may be on the high 
side. Chances may be marginally better tomorrow as the dry layer
becomes more saturated, but we're still well below 10%.

After the upper level front moves through Sunday, much drier air 
will filter in, clearing the mid and upper level clouds by Sunday 
afternoon. The marine layer rarely gets much deeper than 4,000
feet, and it's unlikely to survive as the low moves overhead. 
That should help mix out the low clouds as well. So the sun should
come out tomorrow, but the temperatures will still be stuck in 
the 60s until the 850 temps recover through the week.

&&

.LONG TERM...
Issued at 952 AM PDT Sat Apr 25 2026
(Sunday night through next Friday)

A warming and drying trend will start Monday and continue 
through the week as the 500 mb trough gradually transitions into 
a ridge. Temperatures will climb a few degrees each day, 
eventually reaching mid to upper 70s by Wednesday across the 
interior, and remaining there into the weekend. The marine layer 
will start to reform under the ridge, keeping coastal areas in the
60s through the week. In other words, it will be a pretty nice 
week. It's hard to say what will happen the following week, with 
ensemble clusters split roughly evenly on a continued ridging 
pattern or the return of another trough and unsettled weather.

&&

.AVIATION...
(06Z TAFS)
Issued at 917 PM PDT Sat Apr 25 2026

500 mb low center exits to the east, while 500 mb troughing 
continues late tonight and Sunday. A weak surface cool front also 
moves in from the northwest late tonight and Sunday morning. VFR-
MVFR remains in the forecast with a few areas of light drizzle 
and/or showers tonight and Sunday. 

Vicinity of SFO...VFR-MVFR. A few showers developing tonight and
Sunday morning. Southwest wind 5 to 10 knots tonight through Sunday
morning then gusting to 20 knots Sunday afternoon and early 
evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR-MVFR. Light coastal drizzle and/or 
showers tonight and Sunday. Variable wind directions mainly less 
than 10 knots tonight and Sunday morning becoming westerly near 10
knots Sunday afternoon and early evening. 

&&

.MARINE...
(Tonight through next Friday)
Issued at 913 PM PDT Sat Apr 25 2026

Moderate west to northwest breezes will continue through the
middle of next week before increasing to a fresh to strong
northwest breeze. These stronger winds will build rough seas of
8-10 feet in exposed waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Canepa
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Sat Apr 25 22:30:02 PDT 2026