FXUS66 KMTR 040848
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
148 AM PDT Tue Aug 4 2026

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

.KEY MESSAGES...
Updated at 148 AM PDT Tue Aug 4 2026

 - Moderate HeatRisk in the interior today, becoming patchy midweek

 - Elevated fire weather threat across the interior North and East 
   Bays, and the Diablo and Santa Lucia ranges through the week

 - Widespread Moderate HeatRisk looks to return for the end of the 
   work week. 

&&

.SHORT TERM...
Issued at 148 AM PDT Tue Aug 4 2026
(Today and tonight)

The southerly surge of stratus that arrived earlier on Monday, has 
allowed for stratus to become more widespread this morning. Nearly 
all of our coastline has low clouds along it, with the stratus 
penetrating inland. The Monterey Bay along with the majority of the 
Salinas Valley has filled in, is slowly creeping into Bay Area. 
Expect the marine layer to about 800-1000ft, which should keep high 
temperatures for coastal communities and areas in or under the 
marine layer reasonable. Clouds will begin retreating to the coast 
by mid to late morning, leaving mainly clear skies across the 
region. In terms of the upper level pattern, high pressure will 
slowly take hold of the forecast. 850mb temperatures today, look to 
to be between 24-29C, warmest across the interior. Expect 
temperatures to a bit cooler than yesterday for areas influenced by 
the marine layer, while other locations remain hot. Patchy Moderate 
HeatRisk exists interior North Bay and interior Monterey, with areas 
to widespread Moderate HeatRisk for interior East and South Bays. 
Opted to hold off an issuing a Heat Advisory for these locations 
tonight until we get a better visual on the marine layer expansion 
since that could put interior temperatures at risk.

&&

.LONG TERM...
Issued at 148 AM PDT Tue Aug 4 2026
(Wednesday through Monday)

No major changes to the forecast as high pressure will continue to 
build into the region and then hold through at least Saturday. 
Temperatures will may decrease a more degrees on Wednesday, but it 
will be dependent on the marine layer. Interior locations will still 
be warm, but likely have temperatures in the 90s, perhaps cracking 
100 in a few spots. Warmer and dryer weather starts to return on 
Thursday as the ridge strengthens. Looking at models, 850mb temps 
don't really deviate too much. We're still looking at that airmass 
being warm, around 27-30C, depending on the model. Overnight lows 
would be mild, especially in the thermal belts/mountains. And day 
time highs would climb back into the 90s and low 100s. The HeatRisk 
projection looks to have widespread Moderate HeatRisk for interior 
slots, with pockets of Major HeatRisk. Heat Advisories may be 
needed. 


&&

.AVIATION...
(06Z TAFS)
Issued at 941 PM PDT Mon Aug 3 2026

VFR will continue through the forecast period for the interior
South Bay terminals, then IFR/LIFR developing around 10z for the 
North Bay and Bay Area terminals. IFR/LIFR ceilings returned 
earlier than expected to the Monterey Bay sites and will persist
until early Tuesday afternoon.

Vicinity of SFO...VFR until at least midnight, with high
confidence that IFR/LIFR ceilings will develop overnight. Given
the earlier onset across Monterey Bay sites, there's a slight
chance that stratus returns closer to 08z than 10z. High
confidence that IFR ceilings persist until late morning with a
slight chance of lingering into the early afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR/LIFR ceilings returned a little
sooner than expected with high confidence of persisting into the
early afternoon. VFR through the remainder of Tuesday afternoon
once they lift with a sunset return Tuesday evening. 

&&

.MARINE...
(Tonight through next Sunday)
Issued at 941 PM PDT Mon Aug 3 2026

Light to gentle breezes have set in across our outer waters with
breezier south winds at times and pressure gradient forced
onshore flow across the coastal waters tonight. Northwest seas
will continue to ease and become 4-8ft for the remainder of the
work week. Northwest winds begin to increase and become moderate
by the end of the week into the weekend, with increasing seas
responding by the weekend.

&&

.FIRE WEATHER...
Issued at 420 PM PDT Mon Aug 3 2026

Near critical fire weather conditions continue through this
evening, with elevated fire weather conditions persisting through
the middle of the week, and potentially a return of near critical
conditions later in the week. Temperatures remain around 10 to 15
degrees above normal across the interior (except for Wednesday,
with near normal temperatures) through early next week with highs
in the upper 80s to 90s. No major changes to the forecasted dry 
conditions. Daytime humidity retention remains poor across the 
interior (20-30%) with humidity values dropping into the 10s 
across the interior Central Coast, East Bay Hills/Valleys, and the
higher elevations. Portions of the interior Central Coast may see
daytime humidity values drop into the single digits Tuesday, then
again towards the end of the week into the weekend. Overnight RH 
recovery remains poor at locations above 2,000 feet with values 
between 25 to 40% expected with some favored locations struggling 
to reach even 25%. This will be particularly true across the 
Mayacamas, highest peaks of the East Bay Hills, the Diablo Range, 
the Santa Cruz Mountains, the Santa Lucia and Gabilan Ranges. 
Nocturnal drying (rapid decrease in RH through the pre- dawn 
hours) may also transpire which will increase the burn period or 
time in which fire behavior may remain active. Energy Release 
Component (ERC) values are projected to climb above the the 
percentile across the interior Central Coast, Mid Coast to 
Mendocino (North Bay), and Diablo- Santa Cruz (Diablo Mountains 
and Santa Cruz Mountains) zones by the middle of the week. 
Diurnally breezy onshore winds are expected along the coast, 
mountain gaps and passes, and along the ridgelines each 
afternoon/evening. With near critically dry conditions and above 
normal temperatures expected, individuals across these areas are 
advised to avoid activities that may spark a fire. Fire crews are 
urged to exercise extra caution when executing any prescribed 
burns, especially where fuels, topography, and weather align. 

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...JM
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Tue Aug 4 02:30:02 PDT 2026