FXUS66 KMTR 100440
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
940 PM PDT Sun Aug 9 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1212 PM PDT Sun Aug 9 2026
- Widespread moderate with areas of major HeatRisk for the
interior Sunday
- Elevated to near-critical fire weather conditions in the
higher terrain through Monday
- Minor coastal flooding for bayshore locations along the San
Francisco Bay, San Pablo Bay, and Monterey Bay through Thursday
morning
&&
.SHORT TERM...
Issued at 1212 PM PDT Sun Aug 9 2026
(This evening through Monday night)
A more compressed marine layer allowed for rapid clearing of
stratus to the immediate coastline late this morning. As such,
have left the Heat Advisory in place for much of the interior Bay
Area and Central Coast through 10 PM this evening. However,
locations under the around 500-800 foot marine layer may struggle
to reach their afternoon maximum forecast temperatures. This is
especially so around the San Jose region, yet the southern Santa
Clara Valley has the potential.
Minor coastal flooding is also expected around the time of the
highest high tide (evening/overnight) for bayshore locations along
the San Francisco Bay, San Pablo Bay, and Monterey Bay through
Thursday morning. The decision not to include the Pacific Coast
was made yesterday evening when the forecast fell below the
predicted values, yet still high enough to maintain the
aforementioned bays. Please see the CFW product we have out for
additional details. Also, for more on the fire weather concerns
through early in the week, please see the Fire Weather Section of
the AFD below.
During this weekend's heat event, remember:
* Stay hydrated and drink plenty of fluids.
* Wear lightweight and 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.
Afternoon temperatures are forecast to cool some 5-10 degrees on
Monday as a weak shortwave trough develops off of the West Coast.
As such, HeatRisk levels lower to minor with pockets of moderate.
&&
.LONG TERM...
Issued at 1212 PM PDT Sun Aug 9 2026
(Tuesday through next Saturday)
The troughing would also support coastal drizzle and/or mist each
night and morning through late week. Temperatures cool to below
normal (as much as 20 deg F below by Friday) as a reinforcing
upper level through develops off of the Bay Area and Central
Coast. As this low pressure approaches the coastline late in the
week and monsoonal moisture advects northward around the high over
the Four Corners, there is the potential for high-based
convection. There remains a great deal of uncertainty of whether
or not there will be enough instability aloft to support
thunderstorms. While this is still far out in time and low
confidence, any dry lightning would be problematic from a fire
weather standpoint. Be sure to check back for additional details
as we move closer to midweek.
&&
.AVIATION...
(06Z TAFS)
Issued at 929 PM PDT Sun Aug 9 2026
Currently VFR except for KHAF and the Monterey Bay terminals.
Expect primarily onshore flow, however offshore eddy's are
complicating the inland push of the stratus, producing short
windows of local offshore flow. Should see MVFR/IFR ceilings
materialize after midnight and persist through at least late
morning.
Vicinity of SFO...Offshore eddys should continue to complicate the
exact timing of MVFR/IFR ceilings until after midnight. Given the
uncertainty of how much the eddys will impact how well organized
the marine layer is, maintained late morning clearing instead of
early afternoon indicated by some guidance.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...MVFR ceilings have developed over both
terminals and will persist through late morning with breezy
onshore flow. VFR through the remainder of the afternoon and early
evening with MVFR/IFR stratus ceilings returning near sunset.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 929 PM PDT Sun Aug 9 2026
Fresh to strong northwest winds will persist through the middle
of the week with rough seas up to 12 feet over the northern outer
waters and occasionally the inner waters north of Point Reyes. The
San Pablo, Suisun Bays and the Delta will continue to see gusty
onshore winds through early Monday evening. The long period
southerly swells around 15 seconds will continue through much of
the work week.
&&
.FIRE WEATHER...
Issued at 1206 AM PDT Sun Aug 9 2026
Near-critical fire weather conditions persist today across the
interior due to very hot and dry conditions. Strong thermal
belting, extended burn periods, elevated PIG, and near or record
BI/ERC values are expected. Temperatures will be 10 to 15 degrees
above normal with a compressed marine layer. Poor minimum daytime
relative humidity as low as 10% in the afternoons with little-to-
no recovery overnight is expected with nocturnal drying in the
highest terrain. Even with critically dry conditions, wind is the
limiting factor preventing this from being a Fire Weather
Watch/Red Flag Warning event. Outside of the diurnal sea breeze
that will bring breezy conditions in the afternoons and evenings
through gaps and passes, onshore flow will be light. Additionally,
critical conditions are not expected to meet coverage or duration
requirements to warrant a product. Localized elevated fire
weather conditions in the highest terrain can be expected Monday
due to the combination of recent hot/dry conditions and the
increase in onshore flow. Depending how the pattern and marine
layer evolves, a headline may be warranted and this could last
through Wednesday.
Sarment
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506-
508-529-530.
Heat Advisory until 10 PM PDT this evening for CAZ503-504-510-
512>518.
PZ...Small Craft Advisory until 3 AM PDT Tuesday for SF Bay N of Bay
Bridge.
Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt
Reyes 0-10 nm.
Small Craft Advisory until 9 AM PDT Wednesday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...JM
MARINE...JM
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Prepared by Boulder-Creek.com Weather at: Sun Aug 9 22:30:03 PDT 2026
From the National Weather Service
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