FXUS66 KMTR 250516
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
916 PM PST Wed Dec 24 2025

...New AVIATION, MARINE...

.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...
(06Z TAFS)
Issued at 916 PM PST Wed Dec 24 2025

Radar and satellite imagery show showers across the forecast area
including recent isolated thunderstorms. A strengthening low will
approach far northern California and the Pacific Northwest tonight
through Christmas Day/Night. Southerly winds will re-intensify to
similar speeds last night. Expect low level wind shear through the
evening and overnight, winds easing later Christmas Day. The frontal
system will result in showers, occasionally heavy, including a 
chance of thunderstorms across the area tonight through Christmas
Day/Night.

Vicinity of SFO...VFR-MVFR with showers and a chance of a 
thunderstorm tonight and Christmas Day. Southeasterly wind 
continuing ahead of the next strong frontal system arriving later
tonight and early Christmas Day. Southeasterly wind increasing 
upwards to around 35 knots continuing to 20z Christmas Day, easing
later in the day.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR-MVFR with showers and a chance of a 
thunderstorms tonight and Christmas Day. Southeasterly winds ahead
of the next strong frontal system arriving later tonight and early
Christmas Day; gusts upwards 30-35 knots, easing later in the day.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 912 PM PST Wed Dec 24 2025

...HAZARDOUS MARINE CONDITIONS CONTINUE INTO EARLY FRIDAY...

Southeast breezes across the coastal waters will re-intensify to 
sustained gales from the south by midnight. These dangerous winds 
will be accompanied by a 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 325 PM PST Wed Dec 24 2025

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 until 10 AM PST Thursday for CAZ006-503-505-
     509-517-528>530.

     Wind Advisory until 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.

     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.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Canepa
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Wed Dec 24 22:30:03 PST 2025