Moffett Field, California Weather Forecast Discussion

058
FXUS66 KMTR 260500
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1000 PM PDT Thu Sep 25 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 151 PM PDT Thu Sep 25 2025
- Elevated fire weather risk Friday from wind and relative
   humidity
- Rain and thunderstorms return Monday
&&
.UPDATE...
Issued at 911 PM PDT Thu Sep 25 2025
No update to the forecast this evening as we begin to dry out from
several rounds of rainfall the past couple of days. Marine stratus
has made a comeback tonight. Bay Area coastline may see some
clearing early Friday morning as drier air fills in behind the
exiting upper level disturbance that produced our recent rain.
Monterey Bay and points south are expected to clear out by late
Friday morning. If you`re away from the stratus tonight, clear
skies should provide a good view of a SpaceX Falcon9 Starlink
launch at 9:47p PDT.
&&
.SHORT TERM...
Issued at 151 PM PDT Thu Sep 25 2025
(This evening through Saturday)
There remains a 15% chance for thunderstorms through the afternoon
in Southern Monterey and San Benito Counties as the cut-off low is
proving slow to exit the region. These thunderstorms will pose the
risk of lightning, locally heavy rainfall, small hail, and
erratic/gusty winds. It is difficult to say with certainty if the
marine layer will redevelop tonight as the temperature inversion has
been disrupted due to the recently active weather. If it does,
expect it to be patchy and shallow.
A northerly gradient (and thus northerly, drying winds) will develop
tonight as the cut-off low drifts southeastward to the Colorado
River Valley and high pressure noses in from the Eastern Pacific
Ocean. Minimum daytime relative humidity tomorrow afternoon will be
poor (25%-30%) for the interior with locally lower values of 15% in
Eastern Napa County as this region is within the periphery of
northerly winds down the Sacramento Valley. Fortunately, this threat
will be short-lived with at least moderate recovery (40%)
and the return of onshore flow expected tomorrow night.
Tomorrow, temperatures in the interior will be up to 10 degrees
above normal in the Bay Area and closer to normal in the Central
Coast. Fortunately, as we have just passed Autumnal Equinox and
transitioned from Summer to Autumn, the sun angle will continue to
lower until we reach the Winter Solstice (December 21, 2025). Why is
this important? Well, the lower sun angle will generally make the
heat feel less intense, which is great! Even though this is the
case, it is still important to increase hydration, seek shade during
the warmest parts of the day, and never leave children or pets in
vehicles. Overnight temperatures will cool off enough to open
windows for those of us who do not have air conditioning.
The upper-level shortwave ridge will quickly be broken down by an
upper-level shortwave trough - this will bring temperatures back
down to near normal on Saturday.
&&
.LONG TERM...
Issued at 151 PM PDT Thu Sep 25 2025
(Sunday through next Wednesday)
Global ensemble clusters are in good agreement that the region will
be under the influence of upper-level longwave troughing Sunday
through Tuesday. Just exactly how this takes shape is where it gets
a little fuzzy. There are going to be a slew of low pressure systems
and associated fronts in the Eastern Pacific Ocean by this weekend -
thus, a lot of moving parts. Right now the biggest variation
between the global models of ECMWF and GFS seems to be the timing
with the ECMWF providing an earlier initial arrival time (Monday
morning vs. Monday night). What seems to be certain is that these
systems are going to bring an influx of moisture with them. ECMWF
and GFS IVT (Vertically Integrated Water Vapor Transport) values are
in the 250-500 kg/ms range and our QPF forecast has trended higher
in the last 12 hours. The QPF presentation has taken the shape of
our typical northwesterly to southeasterly gradient with up to 2.00"
in the higher terrain of the North Bay with barely measurable
precipitation of 0.01" down in Southeastern Monterey County. There
is also a chance for thunderstorms during this time.
&&
.AVIATION...
(06Z TAFS)
Issued at 1000 PM PDT Thu Sep 25 2025
Onshore winds will usher coastal stratus and fog /IFR/ inland
until the northerly ACV-SFO pressure gradient (northerly wind)
strengthens tonight. A strengthening northerly wind will then
limit the areal coverage of stratus and fog over the Bay Area
tonight and Friday morning. VFR is forecast on Friday. HREF shows
stratus and fog /IFR/ redeveloping along the north Central Coast
Friday night.
Vicinity of SFO...A westerly wind has at least partially carried
stratus through the San Bruno Gap this evening, IFR stratus ceiling
may still develop through late evening. Then overnight due to an
increasing northerly ACV-SFO pressure gradient and wind, stratus
will likely decrease in coverage increasing the chance of VFR at
SFO. VFR Friday into Friday evening. Westerly wind 5 to 15 knots
tonight and Friday.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus and fog /IFR-LIFR/ continue to
move inland. Strengthening northerly winds over the coastal waters
will likely keep stratus and fog over the Monterey Bay terminals
most of the night except unless until an surface eddy circulation
develops over the Monterey Bay early Friday allowing for an earlier
mix out. Otherwise VFR Friday. Onshore winds 5 to 15 knots except
light southeast wind SNS Airport Friday morning.
&&
.MARINE...
(Tonight through next Wednesday)
Issued at 955 PM PDT Thu Sep 25 2025
Northwesterly winds will become gusty over the northern and outer
waters through Friday. Gale force gusts are likely across the
northern outer waters resulting in rough and steepening seas.
Winds will ease Saturday and then shift to light southerly on
Sunday. A strengthening low pressure system approaches the Pacific
Northwest bringing a cold front with rain to our coastal waters
and bays early next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT Friday for Pt Arena to Pt
     Reyes 0-10 nm.
Gale Warning until 9 PM PDT Friday for Pt Arena to Pt Reyes 10-
     60 NM.
Small Craft Advisory until 3 AM PDT Saturday for Pigeon Pt to Pt
     Pinos 10-60 NM.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...Canepa
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NWS MTR Office Area Forecast Discussion