FXUS66 KMTR 301901
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1201 PM PDT Wed Sep 30 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1201 PM PDT Wed Sep 30 2026
- Elevated fire weather conditions across the higher terrain
through Thursday
- Temperatures warmer than seasonal averages with areas of
moderate HeatRisk across the interior through the week
- Minor coastal flooding near high tide for bayshore locations
along the San Francisco, San Pablo, and Monterey Bays today
through Thursday
&&
.SHORT TERM...
Issued at 1201 PM PDT Wed Sep 30 2026
(This evening through Thursday night)
Mostly clear skies predominate with limited patches of stratus along
the Big Sur Coast. Tonight the stratus deck will come into the North
Bay valleys, the SF and Monterey Bay regions, and the northern
Salinas Valley, with expansion into the interior not expected
tonight. Today marks the first day of warm temperatures as a ridge
sets up over the Western United States, with highs ranging from the
middle 80s to middle 90s in the inland valleys, up to the upper 90s
for the warmest spots in the interior Central Coast, the middle 70s
to middle 80s along the Bays, and the middle 60s to the lower 70s
along the Pacific coast. Highs will be very similar on Thursday.
Winds will be relatively light with an onshore breeze developing in
the afternoon and evening hours, and a push of offshore wind in the
higher elevations of the North and East Bay tonight through Thursday
morning. This morning gusts of 48 mph were reported on Mount St.
Helena and 46 mph at the Santa Fe Geothermal station within the
Mayacamas, with other exposed ridges in the interior North and East
Bays reporting peak gusts in the 25-35 mph range. Expect similar
gusts tonight, resulting in poor overnight humidity recoveries and
elevated fire weather conditions.
Areas of Moderate HeatRisk are starting to pop up across the inland
regions, and expand across the inland regions of the East Bay, South
Bay, and the Central Coast on Thursday. These correspond to a
moderate risk of heat-related illnesses for sensitive populations,
including children, the elderly, pregnant women, people with chronic
illnesses, and people who work or live outdoors without access to
adequate cooling or hydration. Follow these tips to avoid heat
exhaustion and heatstroke:
* 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.
Minor coastal flooding is possible across the bayshore locations of
San Francisco Bay, San Pablo Bay, and Monterey Bay around high tide.
Up to 1.2 feet of inundation above normally dry land is expected,
including up to 0.7 ft of surge caused by thermal expansion and sea
level rise since the sea level datum (basically the point where we
define as "sea level") was set in the 1983-2001 period. At the San
Francisco tidal gauge, high tide is expected to be 1.2 ft above
normal (7.03 ft MLLW) at 2:10 PM Wednesday 9/30 and 1.1 ft above
normal (6.92 ft MLLW) at 2:58 PM on Thursday 10/1.
&&
.LONG TERM...
Issued at 1201 PM PDT Wed Sep 30 2026
(Friday through next Tuesday)
The ridging remains rather resilient through the seven-day outlook
and temperatures remain warmer than the seasonal average through the
week. A notable warming trend will take place over the weekend with
temperatures warming to the 90s into the triple digits (as warm as
102 degrees in the warmest spots of interior Monterey and San benito
Counties). Moderate HeatRisk will become widespread across the
inland locations, and there is a decent chance (40-60% probability)
that areas within the interior East Bay, South Bay, Santa Lucia
range, and interior Central Coast reach Major HeatRisk. That would
correspond to a more widespread risk for heat-related illnesses for
most people, and if this scenario remains on track through the next
day, Heat Advisories for these areas are likely. Longer-range
outlooks suggest that temperatures above seasonal averages are very
likely (70-90% probability) into the second week of October, and
this is supported by ensemble model cluster analysis, where all
clusters agree on keeping some form of ridging around across the
first week of October.
&&
.AVIATION...
(18Z TAFS)
Issued at 1025 AM PDT Wed Sep 30 2026
Developing marine layer is battling building high pressure over
the region. As such, the inversion height is compressed leading to
low CIGs along the coast. That being said, expecting VFR through
early this evening. CIGs return early for MRY/SNS and later for N
Bay and in SF Bay. Moderate conf for fog development tonight given
the shallow nature of the marine layer.
Vicinity of SFO...VRF through this evening. CIGs slowly redevelop
inside SF Bay impacting OAK and SFO 07-09Z timeframe. Lower CIGs
linger into the AM rush for Thursday.
SFO Bridge Approach...Less chc for late night CIGs, but still
expecting some around the approach zone.
Monterey Bay Terminals...VFR through this afternoon, but CIGs
lurking outside of MRY Bay will return early this evening. High
conf on fog impacts by Thursday morning.
&&
.MARINE...
(Today through Monday)
Issued at 1025 AM PDT Wed Sep 30 2026
Northerly winds will continue to ease through the day, but still
hazardous with moderate to strong breezes. Strongest winds are
over the outer waters north of Point Reyes. Conditions will
improve later this week and weekend as northwesterly breezes
diminish to become gentle to moderate. Rough to very rough seas
today will subside to moderate by Friday.
&&
.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 3 AM PDT Thursday for Pigeon Pt to Pt
Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...MM
MARINE...MM
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Prepared by Boulder-Creek.com Weather at: Wed Sep 30 12:30:03 PDT 2026
From the National Weather Service
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