Castro Valley, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

512
FXUS66 KMTR 141750
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
950 AM PST Sun Dec 14 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 1202 AM PST Sun Dec 14 2025

 - Dense fog this morning across the North Bay valleys and East
   Bay interior valleys.

 - Beneficial rain expected this week.

 - Heavier rain and strong wind possible next week.

&&

.UPDATE...
Issued at 841 AM PST Sun Dec 14 2025

Extensive stratus coverage persists across the lower elevations as
the coastal stratus and Tule Fog outgrowth combine. Expecting a
pattern similar to yesterday where the stratus takes its sweet
time to mix out across the region, but does eventually mix out
across most of the interior valleys during the late morning and
afternoon hours, while the coastal regions and the far interior
East Bay remain socked in through the day. At this time, the
temperature forecast is generally on track, but will continue to
monitor observations through the day in case cooler conditions
persist through the day. Touched up the wind forecast a little bit
to account for updated information, but no major changes to the
forecast at this time.

DialH

&&

.SHORT TERM...
Issued at 1202 AM PST Sun Dec 14 2025
(Today and tonight)

We are now on the backside of the 500 mb ridge that dominated the
weather for the last couple weeks. A short wave trough is further
weakening the long wave ridging. This feature brought a strong
southerly surge of stratus on Saturday, but wasn`t enough to mix
out the radiation fog across the valleys. So now we have both
coastal stratus and inland valley fog. Boundary layer averaged winds
have shifted from easterly to southerly over the last 24 hours,
but remain weak at the surface. Dense fog is being reported across
the North Bay valleys and interior East Bay valleys. This fog will
persist through late morning before clearing, and a Dense Fog
Advisory is in effect until 11 AM. Afternoon temperatures will be
cooler than they have been with more cloud coverage and dropping
850 mb temps. Both the long wave ridge and short wave trough will
continue to slide East through the day. There is another good
chance for fog impacts Sunday night as the lower atmosphere
remains poorly mixed.

&&

.LONG TERM...
Issued at 1202 AM PST Sun Dec 14 2025
(Monday through Saturday)

500 mb zonal flow with a tighter pressure gradient will move in by
Tuesday and persist through the week. As this new pattern lines up
with higher moisture it will support a few rounds of light rain.
Without a deep trough there is no real threat of heavy rain this
week. High clouds on Monday will warn of the approaching rain,
with the first round expected Tuesday through Wednesday. The
current forecast has been pretty consistent with around 1/4" in
the North Bay and less than 1/10" everywhere else. While the zonal
flow will persist, drier air will move in Thursday likely
bringing a break in the rain. The next round will move in Friday
and persist through the weekend. Beyond next weekend there is a
lot of uncertainty in the details, but the ensemble cluster
analysis reveals good agreement in the overall pattern evolving to
feature deep troughing just off the coast. This could support an
atmospheric river early next week if the moisture plume lines up
right. The Climate Prediction Center continues to show a moderate
risk for both strong winds and heavy rain from 12/20-12/26.

&&

.AVIATION...
(18Z TAFS)
Issued at 941 AM PST Sun Dec 14 2025

Combo morning with a mix of Tule Fog and marine layer impacting
all terminals in some way. Marine layer depth hovers near 2k feet
per profilers. ACARS and Pireps show tops in the 1400-1600 foot
range. We`re also see some patchy fog, locally dense, too. Based
on latest satellite trends and model guidance will keep a slow
clearing trend in the 19-20Z timeframe for most terminals and
21Z for N and E Bay. Brief VFR late this afternoon before cigs and
fog return early tonight.

Vicinity of SFO...Solid stratus coverage with CIG AOB 1k feet.
Tops showing 1400 feet. CIGS will last through AM rush. VFR this
afternoon with a switch to more onshore flow. CIGS return tonight
and last well into the Monday AM rush.

SFO Bridge Approach...Same as SFO.

Monterey Bay Terminals...Slow clearing through 20-21Z. Early
return this evening in the 00-01Z time.

&&

.MARINE...
(Today through Friday)
Issued at 841 AM PST Sun Dec 14 2025

High pressure over the region will maintain gentle to moderate
breeze continues across the coastal waters today. Southerly flow
will prevail north Pigeon Point and northerly flow will prevail
south of Pigeon Point. Winds increase to moderate to fresh across
the southern coastal waters Monday as the first in a series of
weak systems reaches the coastal waters. Rain chances increase
this week. Low seas persist through the remainder of the weekend
before building to moderate to rough by mid week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory until 11 AM PST this morning for CAZ506-510-
     513.

PZ...Small Craft Advisory from 3 PM to 9 PM PST Monday for Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...MM
MARINE...MM

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