FXUS66 KMTR 220017
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
517 PM PDT Wed Oct 21 2026
...New AVIATION...
.KEY MESSAGES...
Updated at 141 PM PDT Wed Oct 21 2026
- Rain showers expected through Thursday afternoon
- Thunderstorms possible this afternoon into Thursday morning
across north Central Coast
- A warming and drying trend expected for the upcoming weekend
and into early next week
&&
.SHORT TERM...
Issued at 141 PM PDT Wed Oct 21 2026
(This evening through Thursday night)
The greatest potential for thunderstorms will be this afternoon and
evening as up to 400-800 J/kg of MUCAPE (Most Unstable Convective
Available Potential Energy) spreads across the north Central Coast.
We've already seen lightning strikes around the Watsonville area
with ongoing convection off of the coast. The most likely timing of
this will be between now and 10 PM this evening before the cut-off
low pressure system begins to push onshore over central/southern
California and we lose the upper level instability aloft. The SPC
issued a 2-4% tornado probability for the Big Sur coastline, thereby
indicating increased potential for some low-topped supercells. If
the offshore convection moves inland with rotation, there is the
potential for a tornado.
Farther north across the Bay Area and North Bay, cannot rule out an
isolated thunderstorm or two. Rainfall across this region is also
expected to be much lighter with the position of the low pressure
system farther to the south. Across the North Bay and Bay Area,
expecting generally <0.30" with generally 0.25-0.75" across the
north Central Coast, and 0.75-1.25" in the Santa Cruz Mountains and
Santa Lucia Range through Thursday night. Any heavier rain shower
and/or thunderstorm will likely produce brief heavy downpours adding
to the rainfall amounts.
If severe weather does develop, here are some safety reminders:
* Have multiple ways to receive emergency alerts (i.e. NOAA weather
radio, follow NWS Bay Area on social media, and/or ensuring your
phone's emergency alert system is on)
* Move to an interior room away from windows, if a waterspout makes
landfall
* Have an emergency action plan ready if you live downslope of
wildfire burn scars
* Avoid flooded roads. Turn around, don't drown!
Post frontal rain showers are forecast to linger into early Thursday
afternoon with less than a 15% probability for thunderstorms
continuing through the morning. By the Thursday evening, drying
conditions are forecast to return to the region.
&&
.LONG TERM...
Issued at 141 PM PDT Wed Oct 21 2026
(Friday through next Tuesday)
As the upper level through pushes farther inland, periods of
moderate northerly winds are likely across the North Bay Interior
Mountains. Winds across this region have the potential to be 15-25
mph with gusts up to 45 mph Friday night into Saturday morning.
A gradual warming and drying trend will persist across the region as
weak high pressure builds in from the eastern Pacific. Low-lying
areas along the San Francisco Bay, San Pablo Bay, and along the
coast are likely to see minor coastal flooding over the weekend
during peak high tides. This is likely to persist into at least the
middle of the upcoming week.
Weatherwise, there is a great deal of uncertainty beyond Monday as
the weak ridging begins to break down. There is the signal for
additional troughing by late next week bringing cooler and unsettled
weather conditions to the region.
&&
.AVIATION...
(00Z TAFS)
Issued at 517 PM PDT Wed Oct 21 2026
Showers continue to develop and increase in areal coverage over
the forecast area with isolated thunderstorms nearing the southern
coastal waters and southernmost Monterey County. Conditions at
the terminals are VFR with increasing showers resulting in MVFR
possibly briefly IFR surface visibilities tonight and Thursday
morning. Lingering showers Thursday with VFR conditions.
Vicinity of SFO...VFR with showers tonight and Thursday. Surface
winds light and variable becoming westerly near 10 knots Thursday
afternoon and evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR-MVFR with showers tonight and
Thursday. East to southeast winds 5 to 10 knots except increasing
up to 15 knots in the Salinas Valley tonight and Thursday morning.
Winds shifting to westerly near 10 knots Thursday afternoon.
&&
.MARINE...
(Tonight through next Monday)
Issued at 302 PM PDT Wed Oct 21 2026
A cold upper level low will continue to produce showers and
widely scattered thunderstorms tonight. The center of the upper
low will move over Point Conception Thursday morning and then
reach Nevada Thursday night. Expect variable breezes except
possibly gusty in the vicinity of thunderstorms tonight. Northerly
breezes will prevail Thursday through Sunday with locally strong
to near gale breezes across the outer waters Thursday through
Saturday. Moderate seas build to become rough across the outer
waters Friday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 PM Thursday to 9 AM PDT Friday for
Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory from 3 PM Thursday to 9 AM PDT Friday for
Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Canepa
MARINE...Canepa
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Prepared by Boulder-Creek.com Weather at: Wed Oct 21 20:30:03 PDT 2026
From the National Weather Service
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