FXUS66 KMTR 011652
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
952 AM PDT Thu Oct 1 2026
...New UPDATE, MARINE...
.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
&&
.UPDATE...
Issued at 948 AM PDT Thu Oct 1 2026
A Heat Advisory has been issued for Saturday and Sunday across the
Sonoma Coastal Range, the North Bay Interior Mountains, the San
Francisco Bay Shoreline, the East Bay and South Bay, the Santa
Cruz Mountains, the Santa Lucia Range, the interior mountains of
Monterey and San Benito Counties, and the southern Salinas Valley.
High temperatures will reach the middle 90s to near 103, with mild
lows in the higher elevations (upper 60s to middle 70s) limiting
overnight recovery from the warm conditions. Moderate to Major
HeatRisk is expected across the warned area, with impacts to
anyone without adequate cooling or hydration.
Follow these tips to avoid heat-related illnesses this weekend:
* Stay hydrated and drink plenty of fluids.
* Wear lightweight, light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.
DialH
&&
.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...
(12Z TAFS)
Issued at 516 AM PDT Thu Oct 1 2026
Conditions vary from clear /VFR/ inland to stratus and fog /IFR-
LIFR/ along the coastline, in the coastal and inland valleys and
across the San Francisco Bay. Conditions support stratus and fog,
i.e. cooler air relative to sea surface temperatures, nocturnal
radiative cooling to space (dry aloft) plus the longer night-time
hours are bringing cool air valley drainage winds into the mix
with cool winds gently flowing back to the coastline. Above this,
the strong 500 mb ridge is producing a lower level temperature
cap for the marine layer. The marine layer depth is currently 1000
feet. Above the marine layer it's 20F to almost 30F warmer (and
drier). Since the marine layer is currently well structured per
satellite and surface observations (and based on recent NAM, HRRR
output) it'll likely remain a solid presence during the 12z TAFs.
High and mid level clouds arrive tonight and Friday, which may
slow stratus and fog mix out times Friday.
Vicinity of SFO...VFR except tempo stratus /IFR/ 13z-17z this
morning. Stratus /IFR/ is likely to return tonight and Friday
morning 06z-18z. High and mid level clouds arrive from the
southwest tonight and Friday, caveat is these clouds may slow
stratus mix out Friday. Light northwest to northeast wind during
the morning, shifting to northwest and westerly 10 to 15 knots in
the afternoon and evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus and fog /IFR-LIFR/ during the
morning, conditions improving to MVFR-VFR by late morning or
afternoon. Stratus and fog /IFR-LIFR/ returning tonight and Friday
morning. Light and variable winds except cool air drainage winds
up to 10 knots e.g. in the Salinas Valley during the morning.
Winds shifting to onshore 10 to 12 knots in the afternoon and
early evening. Cool air east to southeast drainage winds redevelop
tonight and Friday morning.
&&
.MARINE...
(Today through Tuesday)
Issued at 948 AM PDT Thu Oct 1 2026
Northwest winds will diminish and become gentle to moderate by
late this 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 this afternoon for CAZ006-
506-508-529-530.
Heat Advisory from 11 AM Saturday to 10 PM PDT Sunday for CAZ503-
504-508-510-512>518.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...RGass
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Prepared by Boulder-Creek.com Weather at: Thu Oct 1 10:30:02 PDT 2026
From the National Weather Service
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