Fairfax, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

196
FXUS66 KMTR 100903
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
203 AM PDT Sat May 10 2025

...New SYNOPSIS, SHORT TERM, LONG TERM, MARINE...

.SYNOPSIS...
Issued at 158 AM PDT Sat May 10 2025

Above normal temperatures today will give way to unsettled weather
in the form of below normal temperatures, strong and gusty onshore
winds, light rainfall, and a 10% chance for thunderstorms early
next week.

&&

.SHORT TERM...
(Today and tonight)
Issued at 158 AM PDT Sat May 10 2025

A Heat Advisory remains in effect through 9PM for the Southern
Salinas Valley. Hot conditions can cause heat illness if outdoors
for long periods, especially with physical exertion. Hydration is a
critical piece to mitigating the heat. Drink water, take breaks,
find shade, and if possible, help those who are vulnerable. The rest
of the region (at least away from the immediate coast) will
experience minor HeatRisk and should increase hydration, reduce time
spent outdoors or stay in the shade when the sun is strongest, and
open windows at night and use fans to bring cooler air inside
buildings. The culprit is an upper-level longwave ridge across the
Intermountain West. 850 millibar temperatures are a good proxy for
the air mass as a whole and this afternoon`s (May 10th 00Z) KOAK
sounding observed an 850 millibar temperature of 17.55 degrees
Celsius which is the 90th percentile for today`s date. As is typical
with high pressure and subsequently subsidence, a shallow marine
layer of 400 feet is being observed on the Fort Ord profiler with
stratus shown over Tomales Bay and along the San Francisco Peninsula
Coast. Temperatures will be 10 degrees above normal away from the
immediate coast with no records in jeopardy of being broken.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 158 AM PDT Sat May 10 2025

Heights begin to fall Sunday as an upper-level low develops off the
Pacific Northwest coast, nudging the upper-level longwave ridge to
the east. Sunday`s sensible weather will be 20 degrees cooler than
Saturday`s with strong onshore winds developing in the higher
terrain, gaps, and passes with gusts up to 40 mph to be expected.
Monday will even feel like a Monday weather wise (at least if you
don`t like Mondays or unsettled weather) with temperatures bottoming
out 10 degrees below normal, strong and gusty onshore winds, and
light rainfall for the Bay Area. A surface low will leave the post-
frontal environment with a low probability (10%)/high impact
threat for thunderstorms Tuesday. The necessary ingredients of
lift (cold front with upper-level support, vorticity maximum, 125
knot jet streak at 300 millibars), instability (warm, moist air
below cold, dry air), and moisture (precipitable water value of
0.70 inches) are there, but whether or not they align in time and
space will be the wild card. If a thunderstorm were to develop the
threats include lightning, small hail, and locally heavy rainfall
and gusty winds. The unsettled weather will result in the Oakland
Museum (OAMC1) forecast to approach its daily minimum temperature
records of 47 degrees set in 1974 on Tuesday and Wednesday and 48
degrees set in 1999 on Friday, the official forecast is 50, 50,
and 51 degrees respectively. Heights will be slow to rebuild and
thus temperatures will be slow to warm to seasonal normals
Wednesday through Friday as a Rex Block forms over the Eastern
Pacific Ocean.

&&

.AVIATION...
(06Z TAFS)
Issued at 943 PM PDT Fri May 9 2025

A surface high pressure ridge remains approx 400 miles west and
northwest of the Bay Area with clockwise winds around the high
resulting in northwest winds across the coastal waters. Satellite
imagery shows patchy coastal stratus and fog, elsewhere over the
coastal waters it`s dry enough to support clear /VFR/. The surface
pattern is situated underneath a strong (90th percentile) 500 mb
high pressure system extending northward from SoCal, subsidence
continues to compress the marine layer to near sea level.

It`s a high confidence VFR forecast for the Bay Area airports
through the evening except for coastal stratus developing at KHAF
by mid to late evening. Sufficient late day mixing with drier air
helped extend KMRY and KSNS VFR conditions so far this evening.
However, not fully discounting the 18z/00z NAM 1000 mb humidity
forecasts which lean heavily toward stratus and fog /IFR-LIFR/
redevelopment along the coastline tonight and Saturday morning,
decided to lower visibilities and ceilings early Saturday morning
for the KMRY and KSNS TAFs. Recent NAM output has sped up a few
spot specific 925 mb cooling for Saturday compared to yesterday`s
output. Forecast confidence lowers somewhat with respect to
potential areal stratus/fog coverage late tonight to Saturday
since we`re on the western side of a soon eastward departing 500
mb high pressure system (strongest compression moving with it) and
some disagreement between the HRRR and NAM humidity forecasts for
tonight and Saturday. Fairly thorough cooling is forecast to take
place Saturday and Saturday night throughout the troposphere which
will favor increasing stratus and fog, onshore winds supporting an
inland intrusion later Saturday and Saturday night.

Vicinity of SFO...High confidence VFR forecast for the evening
since the marine layer is compressed to near sea level. Low to
moderate confidence VFR continues late tonight and Saturday
morning. West wind through the 06z TAF, increasingly gusty
Saturday afternoon and evening with IFR-MVFR on the ocean side of
the peninsula and increasing probability of MVFR reaching KSFO
Saturday evening and night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Moderate to high confidence VFR continues
through mid evening, thereafter there`s an increasing probability
of stratus and fog /IFR/ developing for tonight and Saturday morning.
Steady cooling Saturday should increase the marine layer depth
during the day, best chance of VFR will be from late morning to
the afternoon though stratus and patchy fog may still be nearby in
the afternoon for an early stratus /IFR/ intrusion Saturday evening
and night. Onshore winds 5 to 15 knots during the evening, winds
decreasing to generally light onshore tonight and Saturday morning
then onshore 10 to 20 knots Saturday afternoon.

&&

.MARINE...
(Today through Thursday)
Issued at 158 AM PDT Sat May 10 2025

A fresh to strong northwesterly breeze will persist across much of
the coastal waters through the weekend, with up to near gale force
gusts. Light rain will be possible on Monday as a frontal passage
moves across the region. Moderate seas continue through the end of
the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT this evening for CAZ516.

PZ...Small Craft Advisory from 9 AM to 9 PM PDT Sunday for SF Bay N
     of Bay Bridge.

     Small Craft Advisory until 3 AM PDT Sunday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory from 9 AM this morning to 3 AM PDT Sunday
     for Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory until 3 AM PDT early this morning for
     Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory from 9 AM this morning to 9 PM PDT this
     evening for Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 AM PDT Monday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...Canepa

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