FXUS66 KMTR 211921
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1221 PM PDT Tue Jul 21 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1219 PM PDT Tue Jul 21 2026
- Heat Advisory in effect for interior Central Coast and Bay
Area through 9 PM PDT
- Breezy onshore winds return for the second half of the week
- Temperatures will hover around normal through the week
&&
.SHORT TERM...
Issued at 1219 PM PDT Tue Jul 21 2026
(This evening through Wednesday night)
Have went ahead and issued a Heat Advisory through 9 PM this
evening for interior areas of the Bay Area and Central Coast.
Temperatures overnight and into this morning didn't cool off as
much as originally expected, thanks to the mid/upper level cloud
cover across the region. That combined with temperatures forecast
to reach the 90s (potentially exceeding 100 deg F in the warmest
interior spots) across the interior made for widespread Moderate
HeatRisk. Today is forecast to be the hottest of the week!
For tonight, expecting an increase in low level stratus to return
to the coast and expand inland into the coastal adjacent valleys.
There is a greater than 50% probability of this occuring as mid-
to-high level clouds begin to shift to the east as remnant
moisture from Elida gets absorbed in the mean flow aloft. Cannot
rule out coastal drizzle tonight, depending on if the shallow
marine layer is able to redevelop. It will feel muggy once again
tonight as humidity remains elevated.
Tomorrow will feature a significant cool down thanks to an
increase in onshore winds and stronger marine influences.
Temperatures across the interior will warm into the mid 70s to mid
80s with the warmest interior spots reaching into the lower 90s
across the Central Coast. Meanwhile, cooler conditions will
prevail near the coast with day time highs in the mid 60s to mid
70s.
&&
.LONG TERM...
Issued at 1219 PM PDT Tue Jul 21 2026
(Thursday through next Monday)
Not much change to the forecast beyond the short term. Still
expecting troughing off of the Pacific Northwest coast as high
pressure remains over the interior West through late week. This will
generally keep conditions near seasonal averages with night/morning
low clouds working their way inland and then retreating to the coast
by the afternoon. As the high pressure appears to shift more toward
the Four Corners region, we may see the marine layer compress over
the weekend with a slight inland warming trend.
&&
.AVIATION...
(18Z TAFS)
Issued at 1200 PM PDT Tue Jul 21 2026
VFR conditions will prevail with mid-level clouds quickly lifting
to the north leaving behind mostly clear skies. The marine layer
is expected to reform tonight around 1,000 feet which would bring
ceilings on the cusp of IFR/MVFR to bayshore and coastal terminals
with lower confidence farther inland. This may be generous given
the over performance of guidance and models currently, it'll all
depend on if mid-level clouds can clear overnight. Diurnal winds
will prevail.
Vicinity of SFO...VFR conditions with west to northwesterly flow
will prevail. Moderate to high confidence on VFR prevailing
through much of the TAF period. MVFR cigs possible by early
morning Wednesday.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR conditions with moderate
northwesterly winds will prevail. Moderate confidence on ceilings
on the cusp of IFR/MVFR returning tonight.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 1200 PM PDT Tue Jul 21 2026
Light northwesterly breezes are expected today, backing to become
southerly tomorrow. Hazardous conditions for small craft may
return as early as Thursday as northwesterly breezes return and
increase to become moderate to fresh through Saturday. Moderate
southwesterly swell from tropical cyclone activity in the Eastern
Pacific will bring mixed seas and potentially hazardous conditions
through the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT this evening for CAZ502-504-506-508-
510-512>518.
PZ...None.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...CW
MARINE...CW
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Prepared by Boulder-Creek.com Weather at: Tue Jul 21 12:30:03 PDT 2026
From the National Weather Service
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