FXUS66 KMTR 010700
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1200 AM PDT Thu Oct 1 2026

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 1156 PM PDT Wed Sep 30 2026

 - Elevated fire weather conditions across the higher terrain
   Thursday

 - Moderate to major HeatRisk across the interior through
   Wednesday

 - Minor coastal flooding for bayshore locations along the San 
   Francisco Bay, San Pablo Bay, and Monterey Bay Thursday

&&

.SHORT TERM...
Issued at 1156 PM PDT Wed Sep 30 2026
(Thursday and Friday)

The 00Z sounding observed an 850 mb temperature of 21.75 degrees 
Celsius and a 500 mb height of 5880 meters; both of these are near 
the 90th percentile of 20.7 degrees Celsius and 5884 meters, 
respectively. The anomalously warm airmass will yield temperatures 
10 degrees above normal with moderate HeatRisk for the interior. An 
impressive compressed marine layer will keep coastal locations cool 
and lead to reduced visibility during the overnight periods. Another 
morning of offshore flow with dry conditions will bring elevated 
fire weather conditions to the higher terrain. Gusts of 25-35 mph 
are expected with gusts up to 45 mph for the highest and most 
exposed peaks such as Mt. St. Helena. Minor coastal flooding for 
bayshore locations along the San Francisco Bay, San Pablo Bay, and 
Monterey Bay will occur during high tide Thursday afternoon. 
Depending on how Thursday's forecast verifies, the Coastal Flood 
Advisory may need to be extended through Friday evening, at least 
for San Pablo Bay if not all bays.

&&

.LONG TERM...
Issued at 1156 PM PDT Wed Sep 30 2026
(Saturday through Wednesday)

Anomalously high heights, 90th percentile 850 mb temperatures and 
500 mb heights, and EFI values of 0.90 or greater for maximum and 
minimum temperatures all point to it being hot across the interior 
Saturday through Wednesday. Global ensemble clusters are in 
agreement that the heat will peak Saturday as upper-level longwave 
ridging drifts in from the Eastern Pacific Ocean. An upper-level 
shortwave trough will skirt the region Sunday; however, it'll have 
little impact as it merely pauses the warming trend. Upper-level 
ridging will rebuild across the region from the east Monday through 
Wednesday. These subtle changes will have little impact on 
temperatures and HeatRisk with temperatures 10 to 20 degrees above 
normal and widespread moderate with areas of major HeatRisk expected 
across the interior. As is typical for heat events, the greatest 
uncertainty is at the coast due to the marine layer. As it stands 
right now, a compressed marine layer around 500 feet may be able to 
hang on. If it erodes or offshore flow develops in the mornings, 
coastal spots will be hotter than currently forecast. In terms of a 
Heat Advisory, it will likely be for a majority of the interior; the 
soonest it would be in effect would be Saturday with a chance for it 
to linger into early-to-mid next week. As a proxy, eastern San 
Francisco has a 90% probability of reaching 80 degrees on Saturday, 
followed by 70% on Sunday, and 50% Monday through Wednesday. 
Temperatures will cool off overnight; however, the weaker than 
normal onshore flow will bring less relief than normal.

&&

.AVIATION...
(06Z TAFS)
Issued at 1028 PM PDT Wed Sep 30 2026

LIFR ceilings continue to impact coastal terminals through late 
Thursday morning with reductions to visibility becoming more 
prevalent overnight. Medium confidence for IFR to borderline MVFR 
ceilings to develop over the North Bay and south San Francisco Bay 
terminals early Thursday morning. Slightly lower confidence for STS 
to develop ceilings as denoted by the TEMPO group given the 
combination of a weak push of offshore flow and a compressed marine 
layer. Medium to high confidence for SJC and LVK to remain VFR 
through the TAF cycle. Onshore winds gradually ease overnight and 
increase to ~10-15 kt Thursday morning as stratus mixes out.

Vicinity of SFO...VFR as northwest winds gradually ease to ~5-10 kt 
overnight. Higher confidence for borderline MVFR-IFR ceilings to 
impact OAK compared to SFO. While a stratus deck is currently 
hovering over the San Bruno gap, the wind direction is unfavorable 
to allow it to fill over the terminal. Despite this, there is still 
a 50-60% chance for this deck to traverse over the terminal. 
Northwest breezes increase to around 15 kt Thursday early afternoon.

SFO Bridge Approach...Low confidence for widespread ceilings 
overnight. Cloud cover will likely be patchy in nature overnight.

Monterey Bay Terminals...LIFR conditions will continue to impact the 
terminals overnight with reductions in visibility due to mist or 
fog. Medium confidence on exactly when the drastic visibility 
impacts occur. VFR prevails mid Thursday morning into the evening 
before IFR ceilings move onshore again. 

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 1028 PM PDT Wed Sep 30 2026

Moderate to strong northwest breezes persist across the outer
coastal waters with rough wind driven seas. Due to elevated seas,
maritime conditions remain hazardous to small craft through
Thursday, particularly over the outer waters north of Point Reyes.
Northwest winds become gentle to moderate by late Thursday
morning, allowing seas to steadily abate to moderate by Friday.
Marine conditions improve Friday into the weekend.

&&

.FIRE WEATHER...
Issued at 502 AM PDT Wed Sep 30 2026

A high pressure system will move in from the west and compress the
marine layer to approximately 500 feet. Hot and dry conditions
will prevail through late week and weekend. Expect poor overnight
humidity recoveries, with overnight relative humidities as low as
20-30% above the marine layer.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 5 PM PDT Thursday for CAZ006-506-
     508-529-530.

PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

     Small Craft Advisory until 3 AM PDT Thursday for Pigeon Pt to Pt 
     Pinos 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Navarrete
MARINE...Navarrete

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: Thu Oct 1 04:30:03 PDT 2026