FXUS66 KMTR 090709
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1209 AM PDT Sun Aug 9 2026

...New SHORT TERM, LONG TERM, FIRE WEATHER...

.KEY MESSAGES...
Updated at 1206 AM PDT Sun Aug 9 2026

 - Widespread moderate with areas of major HeatRisk for the
   interior Sunday

 - Near-critical fire weather conditions in the higher terrain 
   Sunday

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

&&

.SHORT TERM...
Issued at 1206 AM PDT Sun Aug 9 2026
(Today and tonight)

The 00Z balloon observed a 925 mb temperature of 30.35 degrees 
Celsius (third hottest for the date and time), 850 mb temperature of 
28.75 degrees Celsius (second hottest for the date and time), and 
500 mb height of 5970 meters (record for the date and time). 
Satellite shows stratus clearing off the coast due to a 
strengthening ACV-SFO surface pressure gradient. Northerly/offshore 
flow down the Northern Sacramento Valley Sunday morning will help 
push the marine layer back to the coast. Both of these factors 
should support Sunday being the hottest day of this event; however, 
if the marine layer prevails and northerly/offshore winds don't 
develop we could have a repeat of Saturday with our forecast being 
too hot for the lower elevations. Nonetheless, temperatures will be 
10 to 15 degrees above normal outside of the marine layer influence 
with widespread moderate HeatRisk and areas of major HeatRisk in
the higher terrain. Minor coastal flooding is expected during the
highest high tide (evening/overnight) for bayshore locations 
along the San Francisco Bay, San Pablo Bay, and Monterey Bay 
through Thursday morning. Have opted to leave the Pacific Coast 
out as it would be marginal and overnight if it occurred; however,
high tide may cutoff access to some beaches.

&&

.LONG TERM...
Issued at 1206 AM PDT Sun Aug 9 2026
(Monday through Saturday)

Cooling trend kicks off Monday as upper-level shortwave troughing 
develops off the West Coast. This will moderate temperatures to near 
normal, deepen the marine layer bringing a chance for drizzle, and 
increase onshore flow. A reinforcing trough Wednesday will bring 
more prominent troughing off the West Coast Thursday and into the 
weekend. This along with a resurgence in monsoonal moisture may be 
enough to bring elevated rain showers/thunderstorms to the forecast. 
While there's no mention in the official forecast now, it may be 
warranted as we get closer. 

&&

.AVIATION...
(06Z TAFS)
Issued at 1001 PM PDT Sat Aug 8 2026

IFR-LIFR stratus is making its way inland as the marine layer 
remains close to 1500 feet deep, and expected to make its way into 
the coastal valleys through the night. Warmer air lurking offshore 
is evidenced in the clearing off the coast of the North Bay, but 
there's low confidence for its impacts to the coastal stratus as the 
immediate coast remains under the stratus deck. May need to monitor 
the evolution of the warmer air through the night. Low confidence 
that LVK gets a brief ceiling sometime early Sunday morning. Stratus 
will dissipate through Sunday morning, and breezy onshore flow will 
resume in the afternoon. The high resolution models do show some 
compression of the marine layer resulting in much less stratus 
development, but with similar forecast misses over the last couple 
of days, confidence is low.

Vicinity of SFO... VFR through the next couple of hours with 
moderate northwest winds. Moderate confidence of IFR ceilings 
developing after midnight with dissipation expected late Sunday 
morning. Breezy west winds develop Sunday afternoon and evening, 
with low confidence for stratus impacts Sunday night.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... IFR-LIFR stratus persists through the 
night with light to gentle winds. Stratus will dissipate through 
Sunday morning with breezy onshore winds resuming in the afternoon. 
Low to moderate confidence that stratus returns to the terminals 
Sunday evening a few hours before the end of the TAF period.

&&

.MARINE...
(Tonight through next Friday)
Issued at 1001 PM PDT Sat Aug 8 2026

Fresh to strong northwest winds persist into early next week. In
response, moderate seas build to rough seas up to 12 feet by
Sunday, lasting through the middle of next week. Northern coastal
waters will be hazardous for small craft with occasional near gale
force gusts possible through the weekend. The San Francisco Bay
north of the Bay Bridge into the Delta continues to experience
gusty onshore winds through Sunday night. Long period southerly
swells at around 15 to 17 seconds are still present in the
coastal waters.

&&

.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.

&&

.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 from 9 AM this morning to 9 PM PDT this 
     evening for Pt Arena to Pt Reyes 0-10 nm-SF Bay N of Bay 
     Bridge.

     Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Sun Aug 9 04:30:03 PDT 2026