FXUS66 KMTR 092323
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
423 PM PDT Thu Apr 9 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1134 AM PDT Thu Apr 9 2026

 - Widespread rain showers and thunderstorms this weekend

&&

.SHORT TERM...
Issued at 1134 AM PDT Thu Apr 9 2026
(This afternoon through Friday)

The sky is chaotic over the Bay Area, filled with marine 
layer stratus, mid level cumulus, and high level cirrus all stacked 
on top of each other with sunbreaks in between. The cut-off low is 
now 450 miles due west of the Monterey Peninsula and has picked up 
some speed, now moving at about 15 mph to the West. This system will 
continue at a similar speed and direction for the next 24 hours, 
before it starts to feel the effects of the jet stream, opens up 
into a wave and moves inland to Northern California.

While the sun will come out at times this afternoon, conditions 
will be cooler than the last couple days, and noticeably more 
humid. Dew points are in the mid 50s, with 100% relative humidity 
observed across the majority of cwa in this morning. This humid 
air is thanks to SW winds ahead of the cut-off low pumping 
tropical moisture into California. The PW has remained over 0.9" 
for the last 3 balloon launches going back to Wednesday morning. 
Shower and thunderstorm chances will start later today, but mainly
confined to the North Bay.

More widespread rain is expected by Friday morning. The low pressure 
system will make landfall somewhere along the coast in far northern 
California, bringing a pseudo-cold front to the Bay Area. High 
resolution models are starting simulate this first band of rain and 
the consensus is for an organized, but somewhat weak initial push
of showers moving through from around 2 AM to 9 AM Friday before 
showers become more isolated through the day. Despite the isolated
nature of the showers, there is still a 20% chance for 
thunderstorms in the afternoon, though most of the activity is 
expected in the Central Valley and across the Sierra. All told we 
expect less than 1/4 inch on Friday.

&&

.LONG TERM...
Issued at 1134 AM PDT Thu Apr 9 2026
(Friday night through next Wednesday)

If the rain on Friday leaves you unimpressed, wait until 
the weekend is over before putting your rain boots back in the 
attic. A reinforcing short wave trough will move quickly down from 
the Gulf of Alaska, colliding and merging with the pre-existing cut-
off low and associated moisture. This convergence is expected in the 
afternoon or early evening, which is when the peak of the storm 
activity will arrive to the Bay Area and Central Coast. This frontal 
passage will also serve as a lifting mechanism for convection, which 
is arriving at a good time of day to capitalize on the maximum 
surface based instability generated from afternoon insolation. The 
combination of low-level moisture left over from the tropical air 
mass advection, instability from relatively warm surface 
temperatures quickly cooling with height (850 mb temperatures near 
freezing), and a lifting mechanism from the cold front, are all 
favorable for thunderstorms to develop Saturday afternoon/evening. 
The addition of wind shear delivered from the jet stream allows 
these storms to separate updrafts and downdrafts, prolonging their 
lifespan. If we get enough low-level shear we could even see some 
rotating thunderstorms, and we can't rule out a weak waterspout or 
even brief tornado. Anglers should take special note of the 
expected weather and have a plan to reach safe harbor quickly when
the weather turns. Even without thunderstorms, the marine 
conditions will deteriorate through the day Saturday. If 
thunderstorms develop, the associated wind gusts are capable of 
capsizing small vessels. Fishing leads to more lightning deaths in
the U.S. than any other activity. When thunder roars, head 
indoors!

One change to the forecast is that Sunday now looks more active. It 
should still be a transition day as high pressure starts to rebuild, 
but the rain may not scatter out until the afternoon, rather than 
the morning. Adding it all up, we are expecting anywhere from 1-2" 
across the majority of the Bay Area and Central Coast. That number 
has continued to trend up. The floor of the probabilistic forecast is 
pretty high. There is a 90% chance that SFO gets at least 1" of rain 
according to the ECMWF ensemble. Typically the "dry" scenario is 
much lower for our rainy forecasts, but it seems unlikely that this 
particular storm will be a dud.

Monday still looks dry for now. As the storm breaks, we'll be 
left with cold temperatures. Lows will be in the 40s for most, and
upper 30s in the coldest pockets. A gradual warming trend is 
expected through mid-week, stabilizing near normal with much drier
conditions expected.

&&

.AVIATION...
(00Z TAFS)
Issued at 422 PM PDT Thu Apr 9 2026

Conditions across the region are generally VFR with cumulus clouds 
across the North Bay amd some terrain-driven convection in the far 
interior areas. Moderate winds across the terminals are generally 
onshore with a more southwesterly component as a system approaches 
the region, with the winds expected to last through the evening. 
Later this evening through Friday morning, the first round of rain 
showers is expected to come through the region. The latest high 
resolution model output suggests that the bands may start coming in 
west to east, but will keep the timing in the current TAF forecasts 
intact for now. MVFR-IFR conditions will accompany the showers, with 
conditions improving to VFR-MVFR as the showers move out. There will 
also be isolated to scattered thunderstorms (around a 25-35% 
probability) through Friday afternoon and evening. Considered adding 
VCTS to the terminals of greatest threat, namely STS, APC, and LVK, 
but the confidence in anything developing is too low at this time.

Vicinity of SFO... VFR conditions continue through the next couple 
of hours with breezy westerly winds into the evening. MVFR 
conditions will continue overnight as a band of showers approaches 
the terminal through Friday morning, with VFR conditions with mid-
level clouds returning once the showers pass. Friday afternoon 
should see a moderate southwesterly flow develop through the 
evening. There is around a 20-25% chance of thunderstorms at the 
terminal on Friday, but confidence is too low to put VCTS or PROB30 
in the TAF at this time.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR conditions continue into the evening 
hours with breezy onshore winds through the evening. Monitoring the 
lingering stratus in Monterey Bay in case the timing of the return 
of MVFR-IFR ceilings needs to be adjusted, otherwise they should 
arrive alongside a band of showers early Friday morning. VFR 
conditions return as the showers pass with breezy southwest winds 
developing Friday afternoon. There is a 20-30% probability of 
thunderstorm development at the terminals on Friday, but confidence 
is too low to put VCTS or PROB30 in the TAF at this time.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 422 PM PDT Thu Apr 9 2026

Unsettled weather is forecast Friday through the weekend,
including increasing winds, building seas, and thunderstorms.
Thunderstorms will be capable of producing gusty and erratic
winds, localized heavy rain, small hail, and waterspouts. Gentle
to moderate south to southwest winds will become fresh to strong
by Saturday, with occasional near gale force gusts. Winds become
westerly late Saturday and northerly by late Sunday. Fresh north
winds last through midweek.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Gale Watch from Saturday morning through late Saturday night for 
     Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt 
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Thu Apr 9 18:30:02 PDT 2026