Guerneville, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

262
FXUS66 KMTR 171835
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1135 AM PDT Sat May 17 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 300 AM PDT Sat May 17 2025

Blustery conditions and cooler temperatures begin today and last
through the weekend. Elevated fire weather concerns Monday for
inland areas of the North and East Bay areas due to wind and dry
conditions. Above normal temperatures on tap next week.

&&

.UPDATE...
Issued at 822 AM PDT Sat May 17 2025

Damp start to the day for portions of the Bay Area, mainly along
the coast and coastal mountains. Solid low level moisture through
2500-3000 feet brought drizzle to those areas. One spotter in
Carmel Valley even described it as light rain this morning.
Automated rain gages tipped a few hundredths over the last 6 to 12
hours. The low level moisture was captured nicely on both the KOAK
sounding and Ft Ord profiler. Other item of note this morning are
the winds, especially the East Bay gaps/passes with gusts 40-60
mph. Why so windy? Two words: onshore gradient. The onshore
pressure gradient between KSFO and KSAC is currently 4.6 mb. For
context, any value over 3 mb is considered decent with values
approaching 6 mb is extreme.

Current forecast captures both the drizzle and windy conditions.
No update needed.

For the rest of the day - the onshore gradient is forecast to ease
as the N-S gradient increases. As such, gusty westerly winds will
becoming more northerly. As noted below, gusts up to 50 mph will
be possible. Morning visible satellite is already showing the N-S
gradient kicking in as clouds are rapidly thinning over the N Bay.
Expect some afternoon sunshine, but breezy to gusty conditions.

MM

&&

.SHORT TERM...
(Today and tonight)
Issued at 300 AM PDT Sat May 17 2025

Wind gusts increasing through this morning as a potent upper low
swings through and digs into the Great Basin. As of writing, the
trough axis is situated just offshore of the NorCal/Oregon border
and will continue digging SE today thanks to a robust 130 kt
upstream jet. Surface low pressure developing ahead of the trough
axis will promote a very strong onshore pressure gradient today,
which will help get the gusty conditions going this morning. As
the trough axis moves inland, strong winds will be reinforced
throughout the column as the jet moves overhead. This will kick
off a roughly 30 hour period of robust upper level support and the
best window for gusts of up to 50 mph along ridgetops and the
immediate coastline. Held off on a Wind Advisory given the lack of
spatial extent of expected wind speeds that would meet criteria.
Areas away from the coast can still expect gusts of 35-40 mph.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 300 AM PDT Sat May 17 2025

These windy conditions persist through the weekend until the upper
level support finally moves out of the picture by Monday
afternoon. However, with wind direction changing every so slightly
more northerly overnight Sunday into Monday morning, we are
messaging a brief period of elevated fire weather concerns for
interior areas of the North Bay and East Bay. Conditions are not
critical, but gusty conditions along with dry daytime RH 15-25% on
Monday will certainly lead to some fire weather worries regarding
dry grasses. Beyond Monday, temperatures warm above average as
ridging dominates the pattern the rest of the week.

&&

.AVIATION...
(18Z TAFS)
Issued at 1134 AM PDT Sat May 17 2025

VFR conditions are expected to prevail at the North, East, and South
Bay terminals for the period. The forecast challenge will become the
gusty west to northwest winds where gusts to 25-30kt are expected
this afternoon and perhaps into the early evening hours. KHAF should
be the only site that struggles with cig and/or vis through the TAF
cycle. Some guidance shows low cloud building back in later in the
period, while others keep skies on clearer.


Vicinity of SFO...Clouds this morning generally remain confined to
the terrain surrounding SFO, around San Bruno and along the Santa
Cruz mountains. These clouds should hold through the afternoon which
may lead to some lower clouds slinking through the airspace. Outside
of that, the main concern will turn to the westerly winds. Gusts up
to 30 to 35kt are expected through the evening, though a few
isolated gusts to 40kt might be possible from 22Z to 02Z. Skies
should remain clear at KSFO and KOAK overnight, with some of the
latest hi-res models backing off low cloud making it into the
vicinity of KSFO. Opted to keep the possibility of a FEW MVFR cigs
overnight, but will re-evaluate at the next update.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Satellite imagery shows stratus gradually
gliding along and over the Central Coast. Nearly all of the  hi-res
models show KMRY and SNS staying socked in with MVFR cigs through
early Sunday morning. Decided to follow the that trend from the
previous shift, but also started showing the signs of clearing which
should occur between 12-17Z, with the earlier times favoring KSNS.
VFR conditions are expected to prevail once this happens. In
addition to pesky low clouds, there should be an uptick in west to
west-northwest winds this afternoon at the terminals.

&&

.MARINE...
(Today through Thursday)
Issued at 1134 AM PDT Sat May 17 2025

Hazardous marine conditions will be relentless through Wednesday.
Widespread strong to near gale northwesterly breezes with gale
force gusts are expected today. Winds will become northerly
tonight, remaining strong to near gale with gale force gusts
through Wednesday. Rough to very rough seas are expected through
Wednesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday for Mry Bay-SF Bay N
     of Bay Bridge.

     Gale Warning until 9 PM PDT Sunday for Pt Arena to Pt Reyes 0-10
     nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10
     nm.

     Small Craft Advisory until 3 PM PDT Sunday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Gale Warning from 3 PM to 9 PM PDT Sunday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt
     to Pt Pinos 10-60 NM.

     Gale Warning from 9 PM this evening to 9 PM PDT Sunday for
     Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Behringer
LONG TERM....Behringer
AVIATION...KR
MARINE...KR

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