Coyote, California Weather Forecast Discussion

804
FXUS66 KMTR 291159
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
459 AM PDT Mon Sep 29 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 119 AM PDT Mon Sep 29 2025
- A cold front will bring rain and a slight chance for
   thunderstorms today
- A second cold front will bring renewed rain chances Wednesday
&&
.SHORT TERM...
Issued at 119 AM PDT Mon Sep 29 2025
(Today and tonight)
Fall is here and we have our first wet cold front of the season.
According to the OPC/WPC 06Z surface analysis, the front is
located about 300 miles west of Bodega Bay and will be heading
our way today. We are already seeing widespread southerly wind and
extensive cloud cover ahead of the front. As the cool, dense air
behind the front lifts the warm moist air mass, many of these
clouds will grow dark and bring some rain later today,
particularly for the North Bay. After a recent drying trend in the
forecast, the lastest update has stabilized with around 1/4"
expected in the North Bay and 1/10" along the Peninsula this
afternoon and evening. The rest of the area (East Bay, South Bay,
Central Coast) should only see a few hundredths if anything from
this first cold front. It now looks like the associated surface
low will make landfall around 12Z Tuesday. These landfalling lows
tend to serve as a good trigger for stronger convection if the
environment is unstable. The 06Z HRRR model soundings show surface
CAPE peaking around 200 J/kg this afternoon at Santa Rosa, with
0-6 km shear reaching as high as 50-60 kts ahead of FROPA around
18Z. The ingredients are all there, but they don`t line up
perfectly in time (first high shear, then CAPE, then trigger) and
while the chance for thunderstorms has increased, it remains
slight at around 15% in the North Bay from the late afternoon
through the evening.
&&
.LONG TERM...
Issued at 119 AM PDT Mon Sep 29 2025
(Tuesday through Sunday)
Brief ridging will build in after the first front on Tuesday.
This will bring drier, more stable weather, and perhaps allow the
sun to peak back out. Temperatures will remain suppressed as the
850 mb temperature drops below 10C for just the 2nd time since
June 22 (9.8C 00Z 9/10). This calmer weather won`t last long as a
second cold front arrives Wednesday. This system looks a little
more robust than the Monday system, with the West WRF ensemble
mean IVT peaking around 400 kg/ms and remaining above 250 for
around 30 hours from 30/18Z to 02/00Z. This moisture has the
potential to bring around 1/2" of rain to the North Bay and
between a few hundredths to 1/4" to the rest of the Bay Area.
Again, the Central Coast will be lucky to get more than a few
novelty drops. While the moisture looks pretty robust and the deep
layer shear persists, the instability looks a little more anemic
on Wednesday with 700-500 mb lapse rates around -5 C/km compared
to around -7 C/km on Monday. This should keep the chance for
thunderstorms lower than 10%, but still higher than zero. When all
is said and done, we should be off to a good start for the first
day of the 2026 water year. By Thursday, most of the interesting
weather will be behind us, but the details of the more subtle
pattern become uncertain. The ensemble cluster analysis reveals
significant uncertainty by Saturday with either weak ridging or
weak troughing possible. While there isn`t any real threat of
more rain, the exact temperatures are hard to pin down with this
uncertainty. Our official forecast shows a warming trend, while
the current WPC progs actually bring a dry cold front through on
Saturday.
&&
.AVIATION...
(12Z TAFS)
Issued at 458 AM PDT Mon Sep 29 2025
Light rain showers have reached the Bay Area with temporary
reductions in visibility and ceiling heights possible if showers
move directly over an airport. Scattered showers continue through
early Tuesday morning and are most likely to impact coastal airports
and STS/APC. Ceiling heights have been fluctuating between high end
MVFR (2500-2900 ft) and VFR this morning. Leaned slightly more
pessimistic in the TAFs and kept MVFR CIGs through at least 18Z. It
is likely that we will continue to see temporary improvements to VFR
conditions but these will be temporary with MVFR the prevailing
conditions. Southerly winds continue this morning and gradually
become more SW through the TAF period. Cold frontal passage is
expected to take place between 00Z-12Z with winds easing after
frontal passage. Guidance indicates MVFR CIGs will return towards
the end of the TAF period but confidence is low to moderate in the
exact timing.
Vicinity of SFO...Scattered showers may result in temporary
decreases in visibility and ceiling heights. The first round of
showers continues this morning with showers likely to impact the
airport again tonight. CIGs generally stay VFR but temporary
decreases in ceiling heights may result in MVFR conditions at SFO.
Breezy southerly winds gusting to around 18-20 knots are expected
this afternoon and evening. Cold frontal passage will take place at
SFO late tonight with winds easing and becoming more westerly after
frontal passage. Scattered showers return late Tuesday as another
system approaches the region.
SFO Bridge Approach...Similar to SFO. Scattered showers may result
in temporary reductions in visibility and CIG heights, resulting in
a loss of VAPS, on the SFO Bridge Approach through tonight.
Monterey Bay Terminals...Showers and MVFR conditions continue
through late this morning. Guidance indicates conditions are likely
to improve and become VFR by late morning but confidence is low in
the exact timing. For now, kept CIGs improving by mid to late
morning with winds between 12-15 knots at both MRY and SNS this
afternoon. Showers become more likely late this evening/overnight
with MVFR CIGs likely to return. If a shower moves directly over the
airport temporary drops in visibility and ceiling heights are
possible.
&&
.MARINE...
(Today through Saturday)
Issued at 458 AM PDT Mon Sep 29 2025
Rain showers continue across the coastal waters through early
Tuesday as an upper level trough and surface cold front approach.
Embedded thunderstorms are possible across the northern outer
waters from late this morning through early this evening. A second
system will bring additional rain showers to the waters late
Tuesday into Wednesday. Gentle to moderate southerly winds
generally prevail across the coastal waters through late this
week. Isolated to scattered fresh wind gusts are possible across
the northern waters as each system passes. Seas become moderate to
rough and build to 10 to 12 feet mid to late week and winds are
expected to strengthen again late week into next weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Kennedy
MARINE...Kennedy
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NWS MTR Office Area Forecast Discussion