Bonny Doon California Weather Forecast Discussion

040
FXUS66 KMTR 080015
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
515 PM PDT Tue Oct 7 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 1225 PM PDT Tue Oct 7 2025
- Cool at the coast, with warm conditions everywhere else today
- Cooler and cloudier weather on Wednesday
- Drizzle and light rain arrive towards the second half of the
   week
&&
.SHORT TERM...
Issued at 1225 PM PDT Tue Oct 7 2025
(This evening through Wednesday)
The latest satellite imagery shows status clouds continuing to
linger at the immediate coastal region, with a southerly surge just
now making it to the north of Point Reyes. This is making the
temperature forecast a little complicated for the immediate coastal
region, with the impacts of the southerly surge moderating the
general warm trend that we will discuss just a little later on. For
the latest forecast update, we have bumped down the high
temperatures by a couple of degrees for the immediate coastal
region, where today`s forecast has high temperatures in the lower to
middle 60s.
For the rest of the region, today will mark the warmest day of the
week with moderate offshore flow continuing in the higher elevations
as a weak upper-level cutoff low lurks off of the Central Coast.
High temperatures in the inland valleys range from the middle 80s to
the lower 90s, while the Bayshore sees highs ranging from the lower
to middle 80s. Across the Monterey Bay region, highs in the upper
60s to middle 70s are expected. Patches of Moderate HeatRisk,
corresponding to an elevated risk of heat related illnesses for
sensitive populations, will develop in the Bay Area, including
eastern Marin County, the Bayshore regions of San Mateo County and
the East Bay, and interior Contra Costa County. While offshore winds
would typically increase the fire weather risk across the area, the
recent rainfall in the region, along with the relatively low wind
speeds (with gusts up to 15-20 mph in favored locations) should
mitigate the fire weather concerns.
A pattern change will begin tonight as the upper level low
dissipates, weakening the offshore flow regime, as a stronger trough
develops off the coast of the Pacific Northwest. This will reinforce
a redeveloping onshore flow regime and marine layer, with lows on
Wednesday morning generally dropping to the 50s, possibly the upper
40s in the coolest regions of interior Monterey and San Benito
Counties, and the famed marine layer cloud cover returning to most
of the inland valleys. High temperatures on Wednesday will be
significantly cooler than today`s, with the inland valleys and
Bayshore generally seeing highs in the 70s and Monterey Bay looking
to drop into the upper 60s to near 70.
&&
.LONG TERM...
Issued at 1225 PM PDT Tue Oct 7 2025
(Wednesday night through next Monday)
Near term models continue to depict a chance for coastal drizzle on
Wednesday evening through Thursday morning, with generally light
accumulations expected (a few hundredths of an inch at most). The
drizzle chances switch to rain across much of the Bay Area late
Thursday into Friday, as the upper level low makes its way into the
Pacific Northwest. The latest model runs have slightly backed off
the rain totals, but still expect around a quarter of an inch to
fall across the Sonoma Coastal range, around a tenth to a quarter of
an inch in the northern half of Sonoma County, and up to a tenth of
an inch across the rest of the North Bay. Rainfall amounts in the
San Francisco and Oakland areas reach a few hundredths of an inch
while the interior East Bay, South Bay and Central Coast will be
lucky to see any measurable rainfall. The latest forecast update
also keeps a very slight chance (around 5-10% probability) of
thunderstorms across Sonoma County on Friday afternoon. The models
continue to show a chance for the trough to stall out once it
crosses into the Pacific Northwest on Saturday, but this does not
look to increase the rainfall totals by any significant amount,
although it will keep temperatures cool into the upcoming weekend.
Ensemble models continue to depict a chance for rain towards the
beginning of next week, as another upper level low develops off the
Pacific Northwest, although much remains uncertain about the
forecast evolution. From the previous forecaster Murdock: The
transport of these rains varies as the movements of additional
troughing and low pressures are in poor agreement amongst the long
term models. It looks like the models are struggling, which is kind
of typical for long term forecasts in the shoulder seasons. It will
be interesting to see how the models continue to evolve and
resolve.
&&
.AVIATION...
(00Z TAFS)
Issued at 514 PM PDT Tue Oct 7 2025
.AVIATION...Satellite imagery this afternoon is quiet fascinating on
multiple chancels as you can see an area of low pressure sitting
just off our coastline. It also continues to southerly surge of
stratus while also wrapping around this feature. The low cloud will
likely return this evening for most terminals, bringing with it MVFR
to IFR CIGS, though pockets of LIFR could be possible in addition to
reduced VIS. The marine layer should be around 1000-2000ft by
tomorrow morning, thus the stratus may be able to penetrate into the
East and South Bay terminals. Expect inland clouds to retreat
quickly, while clouds closer to the coast either hold or clear out
by late morning or early afternoon.
Vicinity of SFO...VFR conditions should prevail through the evening
hours, with stratus sneaking back into the TAF site later in the
period. Most guidance has stratus returning around the 9-12UTC mark,
and favors MVFR cigs, though a few suggest the possibility of IFR
after sunrise. Confidence was too low to carry IFR cigs for any
period, thus hinted at the possibility of it. The question then
becomes, how fast will SFO clear out? Uncertainty remains with a lot
of guidance favoring mid to late afternoon. Opted to go with the
more pessimistic outlook with MVFR cigs clearing sometime between
22UTC Wed or closer to 0Z Thu.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...The southern half of Monterey Bay is clear
with VFR conditions prevails. Stratus continues to hug around Santa
Cruz County and the northern part of the Bay, and will likely hold.
Tonight, stratus should return to the Monterey Bay terminals, likely
around 3-5Z. Given last night`s stratus and the model guidance,
opted to go with IFR conditions at KMRY and KSNS, with perhaps a few
bouts of LIFR conditions if the cigs drop substantially and fog
develops once again. Conditions should clear out shortly by late
morning, but some guidance shows MVFR cigs holding until 21Z. Medium
confidence on the clearing time, medium to high confidence on lower
CIGS and VIS for tonight.
&&
.MARINE...
(Today through Sunday)
Issued at 848 AM PDT Tue Oct 7 2025
Expect mostly light to moderate winds accompanied by low to
moderate seas will prevail through early Wednesday before winds
begin to build in the northern outer waters. Winds and seas
continue to increase in the mid week and again into the next work
week. Drizzle chances affect the waters Wednesday and Thursday
with chances for light rain affecting the northern waters late
Thursday through early Saturday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...KR
MARINE...CW
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NWS MTR Office Area Forecast Discussion