Mountain View, California Weather Forecast Discussion

931
FXUS66 KMTR 100005
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
505 PM PDT Tue Sep 9 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 120 PM PDT Tue Sep 9 2025
- Slight (15-25%) chance for thunderstorms in the North Bay during
   the afternoons through Thursday
- Temperatures below seasonal averages and chances for showers
   continue through Thursday
- Warming on Friday and Saturday before another front arrives
   Sunday
&&
.SHORT TERM...
Issued at 120 PM PDT Tue Sep 9 2025
(This evening through Wednesday)
Radar returns are showing isolated showers lingering in some parts
of the Bay Area and Central Coast, with a blob of showers setting up
around 100-200 miles to the west of San Francisco. The chance for
isolated to scattered showers, some of them relatively intense,
continues through the day and into the overnight hours, with
convective probabilities focused on the northern regions of Sonoma
and Napa counties. Probabilities for thunderstorms in the area reach
10-15% this afternoon and evening, with the chances for convection
decreasing as you go southward through the Bay Area. Should
convective showers develop, accumulations could reach a quarter of
an inch, with gusty winds and lightning being the other key hazards.
Outside of thunderstorms, the rain will generally be beneficial,
with accumulations up to one tenth of an inch of rain. Remember:
When thunder roars, go indoors! Or, see a flash, dash inside!
The chance for showers continues into Wednesday, as the deepening of
the upper level low bottoms out, creating rather elevated chances
(15-25% probability) for convective activity in the North Bay during
the afternoon and evening.
High temperatures today and Wednesday will range from the 70s inland
to the middle to upper 60s along the Pacific coast, with lows in the
middle 50s to the middle 60s across the lower elevations. With fresh
rainfall in the region, patchy dense fog is possible in the coastal
regions and cooler valleys. If you encounter patchy fog while
driving, slow down and use low-beam headlights.
&&
.LONG TERM...
Issued at 120 PM PDT Tue Sep 9 2025
(Wednesday night through next Monday)
The chances for showers and thunderstorms will diminish on Thursday,
as the upper level low weakens and crawls eastward, but the current
forecast has chances remaining non-zero throughout the Bay Area. As
the upper level low passes, a brief period of ridging settles in for
Friday and Saturday, with the inland valleys reaching the upper 70s
to the middle 80s, before Sunday brings another cold front and
another chance of rain.
&&
.AVIATION...
(00Z TAFS)
Issued at 451 PM PDT Tue Sep 9 2025
Now that the cold front has pushed through, convective clouds will
dominate through the TAF period. The cloud base is around the
MVFR-VFR threshold, with some isolated light rain showers mainly
impacting the northern terminals. The instability is decreasing
this evening as the sun goes down. Cloud bases will lower
overnight as some marine influence impacts the coastal boundary
layer. Wednesday will bring continued cumulus clouds with a
slight chance for thunderstorms in the northern terminals.
Vicinity of SFO...VFR-MVFR ceilings will remain through the TAF
period due to cumulus cloud bases this evening and a chance for
stratus to return overnight. Even if this happens, the marine
layer is pretty deep and diffuse, so the ceilings should remain
MVFR or higher through the morning. Another round of light showers
are possible Wednesday afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...With drier and more stable air to the
south, MRY and SNS have notably less cloud coverage than terminals
to the North at the moment. On the flip side, this lack of
instability actually increases the chance of stratus forming
overnight. If that happens, there is only a 10% chance that the
cloud base drops below 1,000 feet. When the low clouds clear,
cumulus clouds will become more organized through the day
Wednesday.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 451 PM PDT Tue Sep 9 2025
Gentle to moderate NW winds and moderate seas will continue
through Thursday. By Friday, winds will increase a fresh NW
breeze. Meanwhile, a moderate period NW swell will arrive by
Friday. This swell, combined with the rougher wind waves, will
build moderate to rough seas Friday through Saturday. Otherwise
isolated showers with a slight chance for thunderstorms could
bring locally hazardous conditions this afternoon through
Wednesday night.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Flynn
MARINE...Flynn
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NWS MTR Office Area Forecast Discussion