Lake Berryessa Recreation Area California Weather Forecast Discussion

918
FXUS66 KMTR 120455
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
955 PM PDT Sat Oct 11 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 145 PM PDT Sat Oct 11 2025
- Cool and breezy this weekend
- Widespread rainfall and isolated thunderstorms Monday and Tuesday
   with drier conditions returning by Wednesday afternoon
&&
.UPDATE...
Issued at 650 PM PDT Sat Oct 11 2025
The 00Z balloon measured the precipitable water at 0.74, but a
24 hour drying trend has kicked off that will bring that down to
0.4 or so, and bring more stable conditions Sunday. This drying
will be driven in part by some offshore forcing developing overnight
as high pressure builds over the Great Basin. The SFO-WMC gradient
should drop to -2 mb for a brief period before quickly flipping
back positive through the day Sunday as a jet streak provides
divergence aloft and generates a surface low pressure over Nevada.
TLDR: it will be pretty nice tomorrow.
By late Sunday, a highly meridional jet stream pattern will
support a surface low pressure system over the Pacific NW that
will quickly occlude and dive south, reaching Northern California
by Monday afternoon. Steady rain will precede FROPA, with an
increasing chance for thunderstorms as the surface front moves
through and the cold upper air settles in overnight Monday. Rain
will continue Tuesday, but will be more scattered showers as the
atmosphere battles steepening lapse rates working to decrease the
stability while a drier air mass does the opposite.
The event is now close enough for high resolution models to
simulate how it will unfold, giving us a better idea of the timing.
The much anticipated 00Z NAM just came in and it`s showing an
early band of light rain or likely virga early Monday that will
moisten the atmosphere before the clouds lower and more robust
showers reach the North Bay late Monday morning. This main band
will push south through the afternoon as the intensity steadily
increases. Coastal areas, particularly in the shadow of the Santa
Cruz and Santa Lucia mountains, will likely start the day with
some decent drizzle thanks to orographic lift before the heavier
showers arrive. Monday afternoon and evening now look like the
wettest period with the showers becoming more scattered after
midnight. The best chance for thunderstorms is over the coastal
waters from Monday afternoon to early Tuesday morning, thanks in
part to the high SST anomaly.
Most of this rain will fall in showers. This is not an
atmospheric river. IVT values probably won`t exceed 250 kg/ms, and
the PW shouldn`t get much higher than 1.0. In other words, the
horizontal transfer of moisture is pretty weak. The rain, instead,
will come in the form of on-and-off showers driven by the cold
air aloft and an unstable atmosphere. Some of these showers will
be heavy, but they will come and go. Keep an eye on the radar if
you want to avoid getting soaked.
Flynn
&&
.SHORT TERM...
Issued at 145 PM PDT Sat Oct 11 2025
(This evening through Sunday)
Mid/upper level troughing persist over the West Coast this afternoon
resulting in temperatures about 5 to 10 degrees below seasonal
averages. That said, seeing scattered cumulus over the higher
terrain with afternoon heating. Tonight will be cool with lows
dropping into the mid/upper 40s in the North Bay Valleys and
interior portions of the Central Coast. Elsewhere, upper 40s to mid
50s are expected into early Sunday morning.
There is about a 20%-30% chance of seeing fog in the North Bay
Valleys early Sunday morning before clearing skies return. Sunday
afternoon will feature mostly sunny skies and temperatures in the
60s near the coast to mid 70s across the interior. Cloud cover will
increase late in the day and into Sunday night as a reinforcing
mid/upper level low drops southward down the Washington/Oregon
coastline.
&&
.LONG TERM...
Issued at 145 PM PDT Sat Oct 11 2025
(Sunday night through next Friday)
The aforementioned low will drop down the California coast Monday
afternoon and bring with it rain and isolated thunderstorms. Rain
chances begin early Monday morning across the North Bay and increase
in coverage and intensity throughout the afternoon across the
Central Coast. Precipitable water values are forecast to range
between 0.80-1.00" at this time with CAPE of around 400 J/kg, thus
the potential for isolated thunderstorms. As a colder air mass
filters in from the north, expecting rain showers and isolated
thunderstorms to persist into Tuesday as the mid/upper level low
shifts inland either across the Bay Area or Central Coast on Tuesday
afternoon. Rain chances greatly diminish on Wednesday morning with
drier conditions returning by Wednesday night. Rainfall totals from
Monday through Wednesday currently look to range from 1.50"-2.50
(isolated up to 3.00") in the Santa Lucia Range and in the Santa Cruz
Mountains, with generally less than 1.50" elsewhere. Locally heavy
rainfall will be possible within any stronger rain shower and/or
thunderstorm. This would lead to minor/nuisance flooding concerns
across much of the Bay Area and Central Coast.
Beyond Thursday, there is uncertainty with the progression of the
upper level pattern. However, a general warming and drying trend
looks most likely as a shortwave ridge builds in wake of the exiting
trough.
&&
.AVIATION...
(06Z TAFS)
Issued at 955 PM PDT Sat Oct 11 2025
VFR throughout the region with breezy northwesterly flow steadily
diminishing overnight. Very low confidence (around 20% probability)
for fog impacts in the North Bay valleys, and have improved the
forecast visibility at STS as a result. Developing stratocumulus in
the Santa Lucia range results in a low confidence stratus impact for
MRY overnight. Any developing stratus and fog dissipates early
Sunday morning with breezy and gusty northwest winds resuming in the
afternoon. Towards and after the end of the 24-hour TAF period,
confidence in winds decreases with some models showing the winds
picking up as a strong low pressure system approaches the region.
For now, have kept winds below critical thresholds for the extended
TAFs at SFO and OAK, but will monitor further model guidance through
the next day.
Vicinity of SFO... High confidence of VFR through the TAF period.
Light northwest breezes overnight before stronger winds with gusts
to 25 kt resume Sunday afternoon. Some model data suggests that the
gusts will increase towards the end of the TAF period, but have kept
the gusts below 30-35 kt at this time. Increasing high clouds should
be expected Sunday night in advance of the low pressure system on
Monday.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... High confidence of VFR through the TAF
period at SNS. Developing stratocumulus in the northern Santa Lucia
range may impact MRY overnight, but this is a low confidence
forecast (around 10-20% probability) and the TAF remains VFR
throughout. Will monitor evolution of the clouds overnight. Light
winds overnight before breezy northwest flow resumes Sunday
afternoon. Lower confidence in wind speed and direction towards the
end of the TAF period. Have opted for a "worst-case" scenario in the
TAFs, for lack of a better term, but it is possible for winds at SNS
to be significantly weaker or for northwest winds at MRy to continue
through the end of the TAF period.
&&
.MARINE...
(Tonight through next Friday)
Issued at 955 PM PDT Sat Oct 11 2025
Strong to near gale northerly gusts continue across the waters,
resulting in hazardous conditions with locally stronger winds and
a Gale Warning along the Big Sur coastline. Occasional gale force
gusts are possible on Sunday across the northern waters, and the
windy pattern will persist into early next week. The pattern for
the first half week remains unsettled with more wind and rain
expected.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday for Mry Bay.
Small Craft Advisory until 9 AM PDT Monday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to
     Pigeon Pt 0-10 nm.
Gale Warning until 3 AM PDT Sunday for Pt Pinos to Pt Piedras
     Blancas 0-10 nm.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...DialH
MARINE...DialH
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NWS MTR Office Area Forecast Discussion