FXUS66 KMTR 251657
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
957 AM PDT Sat Apr 25 2026
...New SHORT TERM, LONG TERM, 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...
(12Z TAFS)
Issued at 413 AM PDT Sat Apr 25 2026
Generally MVFR-low end VFR conditions prevail underneath a wide
layer of higher clouds as seen on the satellite imagery. Although
ceilings are expected to lift slightly through the post-sunrise
hours, the high cloud cover should keep the region from scattering
out and ceilings are expected to persist through the TAF period.
Light showers are expected to develop this afternoon and persist
through the night, but these showers should remain non-convective
and not result in major impacts to the flight conditions. Breezy
southwesterly winds will develop in the afternoon, diminishing
overnight.
Vicinity of SFO... MVFR-low end VFR conditions through the TAF
period. Winds will pick up from the west-southwest this afternoon
before diminishing overnight, with lower confidence in the wind
pattern starting Sunday morning. Light showers will develop in the
afternoon and persist through the TAF period.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... MVFR-low end VFR conditions through the
TAF period with southwesterly winds picking up in the afternoon.
Chances for showery rain develop later this morning and persist
through and after the end of the TAF period.
&&
.MARINE...
(Today through Thursday)
Issued at 952 AM PDT Sat Apr 25 2026
Expect mainly moderate west to northwest breezes and moderate
seas through the early part of next week. Drizzle and light rain
remain in the forecast, favoring the southern waters and areas
along the coast this weekend. Strong northwest breezes and rough
seas return towards the middle of next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...Flynn
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Prepared by Boulder-Creek.com Weather at: Sat Apr 25 10:30:03 PDT 2026
From the National Weather Service
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