FXUS66 KMTR 212202
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
302 PM PDT Wed Oct 21 2026

...New MARINE...

.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...
(18Z TAFS)
Issued at 1049 AM PDT Wed Oct 21 2026

Currently VFR with clouds and rain showers pushing in from the 
south. The best chances for thunderstorms are for the Monterey Bay 
terminals this afternoon and this evening, 22Z to 02Z. Elsewhere, 
rain showers are expected through the TAF period, spreading from 
south to north. The best chances for rain showers to occur at a 
terminal will be this afternoon and this evening as coverage and 
intensity increases; however, chances linger through the TAF period 
with wrap around rain showers expected overnight into tomorrow 
morning. Winds will be light and diurnal except when rain 
shower/thunderstorm driven. Low confidence on sub-VFR ceilings 
developing overnight; however, sub-VFR ceilings and visibilities can 
be expected briefly if a rain shower passes directly over a
terminal.

Vicinity of SFO...Currently VFR with northwesterly flow. Clouds will 
continue to lower through the morning with rain showers expected by 
this afternoon. The best chances for rain showers directly at the 
terminal today are between 22Z and 04Z with wrap around rain showers 
continuing through the end of the TAF period. Conditions may improve 
towards the tail end of the TAF period at or after 20Z; however, 
another chance of rain showers is expected during this time as 
the upper-level low pulls east.

SFO Bridge Approach...Relatively higher chance for thunderstorms; 
however, the best chances remain south of SJC. Clouds will lower and 
rain showers will occur sooner than SFO. Clouds at or below FL070 
are expected through the TAF period; however, conditions may briefly 
improve between rain showers.

Monterey Bay Terminals...Currently VFR with southeasterly flow at 
both terminals and rain beginning to be observed at MRY. There is a 
chance for thunderstorms today with the best chances being between 
22Z and 02Z. Rain showers will increase in coverage and intensity 
this evening. Wrap around rain showers are expected overnight and 
into tomorrow morning, likely less in coverage and intensity. Winds 
will be light and diurnal except when rain shower/thunderstorm 
driven. 

&&

.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...Sarment
MARINE...Canepa

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea


  
Prepared by Boulder-Creek.com Weather at: Wed Oct 21 16:30:02 PDT 2026