850
FXUS66 KMTR 281707 AAA
AFDMTR

Area Forecast Discussion...UPDATED
National Weather Service San Francisco CA
907 AM PST Sat Feb 28 2026

...New UPDATE, MARINE...

.KEY MESSAGES...
Updated at 229 AM PST Sat Feb 28 2026

 - Well above normal temperatures today

 - Slight chance (15-25%) for rain with embedded thunderstorms
   possible today in the North Bay

 - Slight cooling trend with light rain likely in the North Bay
   Sunday

 - Above normal temperatures with offshore flow next week

&&

.UPDATE...
Issued at 856 AM PST Sat Feb 28 2026

The current forecast is on track with water vapor imagery
indicating that our shortwave ridging has been replaced with more
in the way of upper troughing. The large scale ascent associated
with this feature has supported the development of showers and
even a few lightning strikes across our offshore marine zones. The
primary PV anomaly is anticipated to lift northward this
afternoon and this translates to a mostly PoP-free forecast after
00Z Sun until 18Z Sun when our next storm system skirts eastward.
We`ll have another look at Sunday`s PoPs with the primary forecast
package as the trend has been for an increase in rain chances
across the North Bay. As noted below, the probability of a tenth
of an inch is only about 10% and that represents the higher end
amount. These higher end amounts are more probable in the upslope
regions of the North Bay and within locations that experience
deeper convective elements. We`ll continue to examine the
thunderstorm potential, particularly given the presence of
instability as manifest by the lightning activity that has been
observed thus far. More information later this afternoon.

&&

.SHORT TERM...
Issued at 229 AM PST Sat Feb 28 2026
(Today and Sunday)

The 00Z sounding observed an 850 mb temperature of 15.35 degrees
Celsius which is the second highest (16.3 degrees Celsius in 1986)
for the date and time. With a warm air mass in place, well above
normal temperatures are expected today. Surface high pressure in the
Intermountain West and a coastal trough off the California Coast
will generate light offshore flow. So not only will we be warm, but
our natural air conditioning (the sea breeze) will be turned off. To
limit heat-related impacts, people should increase water intake,
reduce time spent outdoors or stay in the shade when the sun is the
strongest, and open windows at night and use fans to bring cooler
air inside buildings. We will begin to feel the influence of an
upper-level low in the Eastern Pacific Ocean today, as alluded to by
the high clouds that are beginning to stream in. The first of two
embedded shortwaves will swing through the region today, bringing
with it a slight (15-25%) chance for rain with embedded
thunderstorms possible. The highest probability of occurrence (still
low) will be in the North Bay with ensemble members continuing to
show little to no accumulation today. The second embedded shortwave
will swing through on Sunday, bringing us another chance for rain
and thunderstorms. Measurable rainfall (0.01 inches or greater) is
now looking likely (60% chance) on Sunday for the North Bay -
especially in the higher terrain. If the criteria gets bumped up to
a wetting rain (0.10 inches or greater), the areal extent is
significantly reduced to only the Mayacamas Mountains and Hills of
Western Sonoma County. Thunderstorm chances will remain low (20% or
less) through this upper-level low. The three ingredients needed for
thunderstorm development are lift, instability, and moisture. While
all will be present, they are not expected to overlap favorably in
space and/or time. Sensible weather wise, Sunday will be about 10
degrees cooler than today. For locations south of the Golden Gate
Bridge, drizzle will be possible along the coast and in the higher
terrain.

&&

.LONG TERM...
Issued at 229 AM PST Sat Feb 28 2026
(Monday through Friday)

The upper-level low will begin to fill as it moves through the
region on Monday. As it does so, rain chances will be renewed yet
again Monday morning with light rain possible for the North Bay and
drizzle possible for coastal and higher terrain locations south of
the Golden Gate Bridge. Upper-level shortwave ridging will begin to
nose in from the Eastern Pacific Ocean the latter half of Monday.
The pattern will remain progressive with an upper-level shortwave
trough on the ridge`s heels. There is uncertainty on the location
and the evolution of this feature, and to some extent the strength.
It can be discerned though that this pattern will be conducive for
warm and dry conditions with offshore flow, especially Wednesday
through Friday. Even though we are in Winter with rainfall totals
right around normal for this time of year, it`s never too soon to
think ahead towards "fire season". One side of the fire triangle
(fuels) is right around average for this time of year; however,
Energy Release Components (ERC), Burning Indices (BI), and 100 hour
dead fuel moisture are all expected to be above average by early
next week. While fuels are still projected to remain within the
"significant spread unlikely" range, this is still something to be
made aware of as receptive vegetation will have the potential to
burn, especially on any wind-and-terrain aligned starts. As always,
exercise fire weather safety no matter the time of year.

&&

.AVIATION...
(12Z TAFS)
Issued at 408 AM PST Sat Feb 28 2026

It`s VFR at the terminals. KMUX radar shows high based showers
and/or virga (precipitation evaporating before reaching the ground)
moving in from the west. Farther offshore, lightning strikes are
occurring. Showers and thunderstorms are associated with an eastward
extending 500 mb thermal trough connected to a low center ~ 800
miles offshore. This entire feature will continue to move east-
northeastward through today. There is a slight chance of a shower
including an embedded thunderstorm, but will continue to monitor
radar, satellite and observations before amending to include this in
any of the 12z TAFs. The 500 mb trough axis and incoming convective
potential will reach the Central Valley by late morning. With high
to mid level cloud cover early today, then mixing winds and at least
partial clearing by later today, it`s moderate to high confidence
VFR continues through the morning, afternoon and at least early
evening. Recent high resolution model forecasts however show a
surface cool front and stratus clouds /IFR/ reaching our coastline
tonight with increasing stratus coverage Sunday morning.

Vicinity of SFO...VFR through today and tonight then it`s moderate
to high confidence stratus /IFR/ arrives 11z Sunday morning, staying
IFR through 18z Sunday. Light and variable wind becoming onshore
10 knots by 23z today, onshore wind continues tonight and Sunday
morning. A cool frontal boundary accompanies the stratus intrusion
11z Sunday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through today and tonight then it`s
moderate to high confidence stratus /IFR/ arrives 06z this evening.
Southeast winds 5 knots except up to 15 knots in the Salinas Valley
through morning. Winds shifting over to onshore 10 knots in the
afternoon and decreasing to 5 knots in the evening.

&&

.MARINE...
(Today through Thursday)
Issued at 856 AM PST Sat Feb 28 2026

Average to long northwesterly swell will continue through the
weekend before wave heights and swell periods both decrease.
Rougher seas should be anticipated in and around shower or
thunderstorm activity. The risk for this activity will continue
through Sunday. Seas continue to abate until about mid-week.
Thereafter, conditions will deteriorate as a series of stout
strong systems usher in Gale Force wind gusts and steep seas over
12 feet.

&&

.CLIMATE...
Issued at 1116 PM PST Fri Feb 27 2026

The following are the record high temperatures at the long term
sites for Saturday, Feb 28th.

Location         Feb 28th Record High

Santa Rosa       93 in 1923
San Rafael       78 in 2025
Kentfield        78 in 1929, 1923
Napa             81 in 1929
Richmond         77 in 1986
Livermore        82 in 2022
San Francisco    76 in 1992, 1986
SFO Airport      73 in 1959
Redwood City     77 in 2025
Half Moon Bay    74 in 1954
Oakland Museum   75 in 2025
San Jose         77 in 2025, 1926
Salinas Airport  81 in 2022

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

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

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