FXUS66 KMTR 010555
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
955 PM PST Wed Dec 31 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 1247 PM PST Wed Dec 31 2025
- High astronomical tides combined with storm surge will bring
minor to moderate coastal flooding around high tide through
Sunday.
- A prolonged rainy period starts today.
- Strong southerly winds are likely Friday and into Saturday
morning.
&&
.UPDATE...
Issued at 905 PM PST Wed Dec 31 2025
The steadier rain is pushing towards the north with showers trailing
behind, expected to continue through the night before a more
organized band with more intense rainfall comes through on the
morning of New Year's Day with lingering showers into the evening
hours. The forecast remains on track with temperatures at the stroke
of midnight ranging between the upper 40s to the middle 50s across
the region. Although we do not anticipate any major flooding
concerns with this system, slick roadways and ponding on roads are
still possible tonight, especially in areas with poor drainage or
blocked drains. In addition, coastal flooding is also expected to
build in the morning with around 2 feet of inundation above normally
dry ground expected at high tide (8:41 AM at the San Francisco tide
gauge). People traveling to or from New Year's events are advised to
slow down, allow extra time to reach their destination, and in the
event that they do encounter a flooded or barricaded road, turn
around, don't drown!
DialH
&&
.SHORT TERM...
Issued at 1247 PM PST Wed Dec 31 2025
(This evening through Thursday)
Light to occasionally moderate rain continues to spread northward
and will increase in coverage and intensity through this evening.
This is a result of PWAT values between 1.00-1.30" advecting in from
the south as a mid/upper level cut off low remains just west of the
Central Coast. As the low pressure shifts into the Central Coast on
Thursday morning, there will be a slight chance of thunderstorms
late morning into the afternoon over this region. By late Thursday
afternoon and into the evening, rain will be more focused along the
coastal terrain as a warm front moves northward across the region.
Rain shadowed valleys may not see any rainfall from Thursday
afternoon through about Friday night.
&&
.LONG TERM...
Issued at 1247 PM PST Wed Dec 31 2025
(Thursday night through next Tuesday)
A more typical atmospheric river is set to move through the
region late Friday and into early Saturday morning. This is when
more widespread rain and stronger winds are forecast. Wind 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 night through
Saturday morning. Wind Advisories are likely during this time
frame, yet the forecast models have trended about 6 hours later
from yesterday. So, still refining the forecast as we move closer
to the event. From 4 PM Friday through 4 PM Sunday, rainfall
totals will range from 2.00- 4.00" in the coastal ranges,
1.50-3.00" in the North Bay, 1.00-2.00" in San Francisco and other
coastal areas, and generally less than 1.25" in the rain shadowed
valleys. There is generally less than a 20% chance of
thunderstorms as the main frontal band moves through and in wake
of the passage through Sunday afternoon. Given the recent rainfall
from last week, this will lead to nuisance flooding for poor
drainage areas, urban areas, and rises on flashy creeks/streams.
This will be especially so if a heavier rain shower and/or
thunderstorm where to move over any give area. However, widespread
river flooding is not anticipated at this time.
From the previous forecaster: "A new low pressure system and
associated cold front is possible Monday or Tuesday. The ensemble
clusters have differing opinions on the strength and timing of
this feature, but they all show a trough off the coast, which is
enough to keep rain chances around through the entire 7-day
forecast period. KMUX will stay in precip mode for the foreseeable
future."
&&
.AVIATION...
(06Z TAFS)
Issued at 941 PM PST Wed Dec 31 2025
Widespread light rain continues across our entire service area and
is expected to persist through the overnight and most of the day
Thursday. MVFR is expected to prevail for North Bay and Bay Area
terminals, however KSJC continues to hover between IFR/LIFR when
steadier periods of light/moderate rain move through.
Vicinity of SFO...Bay Area terminals have seen cigs drop into IFR
when rainfall intensity increases, however MVFR cigs are expected
to prevail through most of the forecast period.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Steady VFR this evening, despite more
pessimistic guidance, thus will keep persistence forecast through
the overnight hours with a return to MVFR ceilings Thursday
morning, and a possible break in rain by early evening Thursday.
&&
.MARINE...
(Tonight through next Tuesday)
Issued at 905 PM PST Wed Dec 31 2025
Small Craft Advisory conditions have settled over both our outer
and coastal waters, and will remain in effect until Friday
morning, when southerly winds increase to gale force. Gale Force
Warnings will expire early Saturday morning, when winds begin to
gradually ease. Expect light to moderate rainfall to persist
through the weekend, with a slight chance of thunderstorms early
Thursday morning as the center of the upper level low crosses into
our outer waters from the south, and then once again Friday into
Saturday with the arrival of a second, stronger system. Rain
chances and breezy winds will continue into the beginning of next
week.
&&
.BEACHES...
Issued at 859 AM PST Wed Dec 31 2025
Perigean spring tides (King Tides) will impact the region through
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 southerly winds, generating some storm
surge. The combination of these factors will bring minor to
moderate coastal flooding to the low-lying areas near shorelines
and tidal waterways during high tide through Sunday. At the San
Francisco tidal gauge, high tide is expected to be 2.0 ft above
normal at 8:41 AM Thursday, 2.2 ft above normal at 9:34 AM Friday,
2.2 ft above normal at 10:26 AM Saturday, and 1.8 ft above normal
at 11:18 AM Sunday. These predictions include up to 1 foot 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 until 2 PM PST Sunday for CAZ006-505-506-
508-509-529-530.
PZ...Small Craft Advisory from 9 AM Friday to 3 AM PST Saturday for
SF Bay N of Bay Bridge.
Small Craft Advisory from 9 AM to 9 PM PST Thursday for Mry Bay.
Small Craft Advisory until 3 AM PST Friday for Pt Arena to Pt
Reyes 0-10 nm.
Gale Warning from 3 AM Friday to 3 AM PST Saturday for Pt Arena
to Pt Reyes 0-10 nm.
Small Craft Advisory until 3 PM PST Friday for Pigeon Pt to Pt
Pinos 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.
Gale Warning from 3 PM Friday to 3 AM PST Saturday for Pigeon Pt
to Pt Pinos 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.
Small Craft Advisory until 9 AM PST Friday for Pigeon Pt to Pt
Pinos 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt
Piedras Blancas 0-10 nm.
Gale Warning from 9 AM Friday to 3 AM PST Saturday for Pigeon Pt
to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos
to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...JM
MARINE...JM
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Prepared by Boulder-Creek.com Weather at: Wed Dec 31 22:30:02 PST 2025
From the National Weather Service
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