FXUS66 KMTR 242144
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
144 PM PST Wed Dec 24 2025
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1238 PM PST Wed Dec 24 2025
- Strong and damaging winds return overnight and continue through
Thursday.
- A flood watch remains in effect through Friday evening across
the region. The main threat is flash flooding and landslides
from high rain rates.
- Slight chances for severe thunderstorms begin this evening and
continue through Thursday. Severe threats include damaging wind
gusts and possible tornadoes.
- Dangerous beach and marine conditions continue through Friday
across the Pacific coast and adjacent beaches.
- Cold temperatures settle in this weekend after the storms
break.
&&
.SHORT TERM...
Issued at 1238 PM PST Wed Dec 24 2025
(This evening through Thursday)
The skies have cleared better than expected today giving us a
short, but remarkably nice break between last night's wind storm
and the upcoming system. The initial round of showers could reach
the Santa Cruz/San Mateo coast as early as 3 PM. This is a
prefrontal trough that won't bring the primary impacts expected
overnight, but is currently producing thunderstorms over the
coastal waters that could survive until landfall. With the bonus
sunshine, temperatures are climbing higher than expected and
that's translating to a better convective environment. Santa Rosa
has been under clear skies since the sun rose this morning and is
currently reporting a temperature of 61 degrees, well above the
56 we had for the maximum today. This extra surface heating will
play a role in the instability going into the evening hours. The
environment ahead of tonight's storms look pretty good for
thunderstorms and even tornadoes. The 18Z RAP shows the following
parameters at SFO compared to the preferred value for supercell
tornadoes in parentheses. 0-1km shear: 40 kts (20), MLCAPE: 209
J/kg (1500), Significant Tornado Parameter: 0.3 (1.0), MLCIN: -2
(>-25), Effective Storm Relative Helicity: 242 m2/s2 (150),
Effective Bulk Wind Difference: 44 kts (40). This is a high-shear,
low CAPE set-up, but the increased surface temperature and high
dew points from last night's rain are helping the surface based
convection chances. In fact, our next shift just walked in and one
of the meteorologists said it feels like Kansas in May out there.
The main impacts are expected through the overnight hours and will
be similar to last night. The winds may be a notch lower, but the
severe thunderstorms chances are a notch higher. The other
difference compared to last night is how much longer the winds
will linger into the following day. The parent low pressure system
will not push inland, but rather linger off the coast while
gradually weakening. This will keep southerly winds elevated
through the day Thursday, while pushing through a couple bands of
showers. The peak of the impacts are still expected in the middle
of the night, but we won't get the quick reprieve that we saw
this morning. It will still be breezy while the kids try out their
new bikes and basketballs Christmas morning. Scattered showers
will be a threat through the day.
&&
.LONG TERM...
Issued at 1238 PM PST Wed Dec 24 2025
(Thursday night through next Tuesday)
Starting in the early morning Friday, winds and shower activity
will gradually decrease as the low pressure system offshore opens
up into a trough and moves into northern Oregon. The associated
surface trough axis will move across the Bay Area Friday evening.
This will finally flip the winds back to northerly, bringing
drier, cooler weather for the weekend. The 1000-500 mb thickness
actually increases this weekend, with the cooling coming mainly from
enhanced radiation during in the cloudless nights. Sunday through
Tuesday look particularly calm, clear and cool as a 500 mb ridge
sets in. The next troughing pattern looks probable on the 1st or
2nd, just in time for King Tides. There's no strong signal for
major impacts yet, but the CW3E ECCC AR Activity tool shows higher
than normal chances for atmospheric rivers through the first half
of January.
&&
.AVIATION...
(18Z TAFS)
Issued at 941 AM PST Wed Dec 24 2025
A favorable weather window exists today in between 2 very intense
wind storms. The initial front has moved through allowing winds
to decrease significantly through the morning. In fact, the cloud
shield will also clear out over the next few hours, bringing some
sunshine and VFR conditions across the terminals this afternoon.
The break won't last long, however, as a second rapidly deepening
low pressure system moves up the coast. This will cause southerly
winds to re-intensify overnight, reaching very similar speeds as
last night. The difference is that the winds will linger longer
into Thursday as the low stalls offshore rather than moving
inland. High resolution guidance is also hinting at 2 distinct
bands of precipitation overnight associated with the passage of
the warm and cold fronts. Both of these bring a chance for
thunderstorms, some of which could be strong. Scattered showers
could persist in the cold air mass into Friday as the winds
gradually ease.
Vicinity of SFO..Fortunately the timing of the light winds and
clearing skies lines up with the busy midday period at SFO, and
the west plan should hold until at least 00Z before the stronger
southerly winds return. The exact timing of this in a little
uncertain. The 925 mb winds ramp up around 00Z, and the increasing
sunshine may help mix them down to the surface. The TAF is a
little more optimistic, suggesting it will take a couple hours
before the terminal sees southerlies increase over 10 kts. After
they do, conditions will gradually deteriorate through the evening
with another round of very strong winds, showers, and possible
thunderstorms overnight.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Surface winds are surprisingly northerly
at both MRY and SNS, but that will surely flip back to southerly
over the next 3 hours as the pressure gradient increases ahead of
the wind storm tonight. Before the storm gets here, there is a
favorable weather window through the daylight hours with moderate
wind and VFR conditions. As the sun goes down winds will gradually
ramp up and scattered, but persistent, showers will move through
from Wednesday night into Thursday morning. Some of these showers
will be strong, with a decent chance for thunderstorms at both MRY
and SNS in the early morning hours.
&&
.MARINE...
(Today through Monday)
Issued at 941 AM PST Wed Dec 24 2025
...HAZARDOUS MARINE CONDITIONS CONTINUE INTO EARLY FRIDAY...
After an intense wind storm overnight, winds have eased to a
moderate SE breeze across the coastal waters, but will gradually
re-intensify to sustained gales from the south by midnight. These
dangerous winds will be accompanied by a good chance for
thunderstorms and possible waterspouts through the early morning
hours Thursday. Seas will rebuild to very rough from the choppy
wind waves. These hazardous seas will linger through Friday,
reinforced by a moderate westerly swell. If your vessel is not
able to handle these conditions return to port or seek protected
waters as soon as possible.
&&
.BEACHES...
Issued at 355 AM PST Wed Dec 24 2025
The strong winds along the coast will result in hazardous beach
conditions. A Beach Hazards Statement has been issued for the
coast through 4AM Friday. The main concerns include:blowing and
drifting sand and wind waves up to 20 ft. The drifting sand and
increased sea spray will also result in poor visibilities,
affecting water rescues. Increased coastal erosion will be
possible as well.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through late Thursday night for CAZ006-
505-509-529-530.
Flood Watch through Friday evening for CAZ006-502>506-508>510-
512>518-528>530.
High Wind Warning from 8 PM this evening to 10 AM PST Thursday
for CAZ006-503-505-509-517-528>530.
Wind Advisory from 8 PM this evening to 10 AM PST Thursday for
CAZ502-504-506-508-510-512>516-518.
PZ...Gale Warning until 3 AM PST Friday for Mry Bay-Pigeon Pt to Pt
Pinos 10-60 NM-SF Bay N of Bay Bridge.
Small Craft Advisory until 3 PM PST this afternoon for Mry Bay-
Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60
NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60
NM-Pt Reyes to Pigeon Pt 0-10 nm.
Storm Warning until 3 AM PST Friday for Pigeon Pt to Pt Pinos 0-
10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-
60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to
Pigeon Pt 0-10 nm.
Gale Warning until 3 PM PST this afternoon for Pt Pinos to Pt
Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Flynn
MARINE...Flynn
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Prepared by Boulder-Creek.com Weather at: Wed Dec 24 14:30:02 PST 2025
From the National Weather Service
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