FXUS66 KMTR 310355
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
755 PM PST Tue Dec 30 2025
...New UPDATE...
.KEY MESSAGES...
Updated at 202 PM PST Tue Dec 30 2025
- Rain returns and becomes widespread for New Years Eve
- Friday is likely to be windy with strong southerly winds along
with locally heavy rainfall
- Coastal flooding from King Tides is expected Wednesday through
Sunday
- Unsettled conditions look to prevail through at least early
next week
&&
.UPDATE...
Issued at 740 PM PST Tue Dec 30 2025
Deeper cloud features streaming in from the south, evident via
current satellite. Still a pretty remarkable dry layer in the
low-to-mid levels of the atmosphere, so any precipitation that may
fall out of the clouds overnight will have some work to do to
cool and moisten that layer. By mid-morning tomorrow, the dry air
will likely be overcome, giving way to a few showers beginning
along the Central Coast. We'll need to watch more closely going
into the evening and overnight hours tomorrow when a more vigorous
upper level wave is progged to move across the Central Coast,
alluding to a chance of isolated thunderstorms. Otherwise no major
updates to the forecast for the upcoming storm system.
Behringer
&&
.SHORT TERM...
Issued at 202 PM PST Tue Dec 30 2025
(This evening through Wednesday)
Temperatures are struggling to warm this afternoon as low clouds
remain trapped beneath the high clouds advecting north across the
region this afternoon. As of this writing, temperatures remain in
lower-to-mid 40s in much of the North Bay and East Bay valleys.
However, coastal areas have warmed into the 60s and even lower 70s
across the Central Coast where offshore flow persists. That said,
minimum temperatures overnight are forecast to be warmer than
previous nights as increased moisture and cloud cover continue to
spread northward in advance of an approaching weather system.
By Wednesday morning much of the Central Coast will be experiencing
light to moderate rain that will then spread northward across the
Bay Area and North Bay throughout the afternoon and evening.
However, locally higher amounts are expected in the Santa Lucia and
Sierra de Salinas ranges where there is a marginal risk for
excessive rainfall on Wednesday and Thursday due to orographic lift.
Given the recent rainfall, this will lead to nuisance flooding for
poor drainage areas, urban areas, and rises on flashy
creeks/streams.
&&
.LONG TERM...
Issued at 202 PM PST Tue Dec 30 2025
(Wednesday night through next Monday)
Rain will continue on New Years Day, yet not as heavy or widespread
as Wednesday as the mid/upper level cut-off low pushes inland over
southern California.
By Friday, an atmospheric river is forecast to move across the North
Bay and then progress southward bringing additional rainfall to the
region and a 10-15% chance for thunderstorms. This is when we are
expecting the heaviest of rainfall, however the boundary does not
appear likely to stall at any given point. There is a marginal risk
for excessive rainfall on Friday across the interior Bay Area and
Central Coast. Southerly winds will also be strong and gusty on
Friday, especially ahead of and along the main frontal boundary that
is forecast to move through the Bay Area and Central Coast Friday
afternoon and evening. Gusts are currently forecast to be 45-55 mph
along the coast, in the higher terrain, and northwest to southeast
oriented valleys. Elsewhere expecting 35-45 mph gusts from late
Friday morning through the evening and potentially into early
Saturday morning.
Rainfall amounts and wind speeds will be better refined as we get
closer to the event. Unsettled conditions look to prevail into the
weekend and potentially into early next week as the pattern aloft
remains troughy.
&&
.AVIATION...
(00Z TAFS)
Issued at 327 PM PST Tue Dec 30 2025
High clouds continue to expand over our area out ahead of a
developing upper level low that will bring showers toward the end
of the TAF period Wednesday. Short-term hires guidance suggests
the potential for fog development in the North Bay overnight,
that may be complicated by the upper level cloud cover inhibiting
radiational cooling, thus the potential for fog is low confidence.
Otherwise VFR is expected to prevail through the TAF period for
most locations, however MVFR ceilings are possible late in the
forecast period.
Vicinity of SFO...VFR is expected to prevail through the forecast
period with scattered showers and possible MVFR cigs late in the
period with relatively light easterly surface winds.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR is expected to prevail through the
TAF period with scattered light showers and MVFR cigs possible
late in the TAF period and relatively light E-SE surface winds.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 327 PM PST Tue Dec 30 2025
Moderate to fresh east to northeast winds and moderate seas will
continue through Wednesday. Fresh to strong southerly breezes
begin to increase Thursday into Friday when gale force gusts
become more likely. Building seas will become rough Thursday into
Friday. We'll see an increase in coverage of rainfall over our
waters Wednesday, then again on Friday, when we'll see stronger
winds and potential for isolated thunderstorms.
&&
.BEACHES...
Issued at 925 PM PST Mon Dec 29 2025
Perigean spring tides (King Tides) return Wednesday - Sunday.
This is due to the combination of the full moon on 1/3, lunar
perigee on 1/1, and perihelion on 1/3. In other words all three
planetary bodies are lined up and close to each other. In addition
to the high astronomical tide, the incoming low pressure system
will bring strong onshore winds, generating some storm surge. The
combination of these factors will bring minor coastal flooding to
the low-lying areas near shorelines and tidal waterways during
high tide Wednesday through Sunday. At the San Francisco tidal
gauge, high tide is expected to be 1.5 ft above normal at 7:51 AM
Wednesday, 1.7 ft above normal at 8:41 AM Thursday, 1.8 ft above
normal at 9:34 AM Friday, 1.8 ft above normal at 10:26 AM
Saturday, and 1.6 ft above normal at 11:18 AM Sunday. These
predictions include 0.5 feet of storm surge that will enhance the
astronomical tide and flooding threat. High tide varies up to 90
minutes earlier or later along the Pacific Coast and through the
San Francisco Bay, respectively.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 5 AM Wednesday to 2 PM PST Sunday
for CAZ006-505-506-508-509-529-530.
PZ...None.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...JM
MARINE...JM
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Prepared by Boulder-Creek.com Weather at: Tue Dec 30 20:30:03 PST 2025
From the National Weather Service
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