Millbrae, California Weather Forecast Discussion

753
FXUS66 KMTR 240459
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
959 PM PDT Tue Sep 23 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 140 PM PDT Tue Sep 23 2025
- Areas of Moderate and Major HeatRisk today.
- Chance for showers and thunderstorms overnight through Thursday
   morning.
- Any Bay Area thunderstorms could be dry, while the Central
   Coast is expected to receive wetting rain.
&&
.UPDATE...
Issued at 927 PM PDT Tue Sep 23 2025
The forecast for showers and thunderstorms to gradually lift north
into the Central Coast overnight remains on track. There are some
elevated showers brushing southern Monterey County at this hour,
that will continue to move offshore, with stronger echo`s farther
west over open water, also drifting northwest. There were some
elevated thunderstorms in our southern outer water earlier this
afternoon but both our land and water environments would be
characterized as stable for at least the next few hours, until the
warm sector of the slow moving system lifts farther north.
&&
.SHORT TERM...
Issued at 140 PM PDT Tue Sep 23 2025
(This evening through Wednesday)
Clear skies and light offshore wind this morning have caused
temperatures to climb 5-10 degrees warmer than this time
yesterday. Many inland stations are in the upper 90s with Novato
recording 102 degrees at 12:55. The heat is also making it to the
Bay shore, with downtown San Francisco recording 87 (warmest
since last October) and San Carlos 91. The winds are shifting to
onshore as the sea breeze develops, which should reverse the
warming trend on the coast.
A significant pattern change is in store overnight as a cut-off
low pressure system with ample subtropical moisture pushes in
from the south. We can say with high confidence that this will
bring significant cloud cover, cooler temperatures, and higher
humidity. There`s also a good chance for showers and possibly
thunderstorms across the Central Coast Wednesday morning. There
could be up to 1" of rain in the Santa Lucias, with closer to
1/10" in northern Monterey County. Confidence is a little lower
regarding the convective potential further north, but there is
still a chance for thunderstorms in the Bay Area through the day
Wednesday. The lower levels of the atmosphere are much drier in
the Bay Area, however. While the chances are lower, if any
thunderstorms develop over the Bay Area, it`s less likely wetting
rain will reach the ground. This dry lightning threat follows a
warm, dry period, bringing an elevated chance for wildfire
ignition. The latest trend in the CAMs is to bring renewed shower
chances early Thursday after a lull in activity Wednesday evening.
&&
.LONG TERM...
Issued at 140 PM PDT Tue Sep 23 2025
(Wednesday night through next Monday)
More seasonal weather returns by Thursday afternoon as the skies
begin to clear and temperatures return to normal. There is another
chance for rain early next week, this time from a cold front.
Ensemble cluster analysis reveals significant timing and strength
uncertainty, but it`s the next one to watch for rain chances.
&&
.AVIATION...
(06Z TAFS)
Issued at 959 PM PDT Tue Sep 23 2025
A 500 mb low pressure center is located 250 miles southwest of
Monterey and it`s forecast to move steadily northeastward reaching
near Monterey this time Wednesday. Except for patchy stratus and
fog /IFR/ over the northern Monterey Bay Area it`s VFR over the
forecast area this evening. However clouds, showers and thunderstorms
are rotating around the low to our southwest and will continue to
advance northward tonight and Wednesday. Stratus and fog /IFR/
patches remain possible along the coast while for the most part
high based clouds, showers and thunderstorms will prevail with the
potential for gusty outflow winds and heavy rain. With the cold
core low over the north Central Coast Wednesday night and Thursday
morning expect additional heavy showers and thunderstorms into
Wednesday night and early Thursday morning. As activity is forecast
to increase tonight and Wednesday, with the potential for quickly
changing weather - monitoring radar, satellite and observations
will become increasingly important with TAF amendments issued as
needed.
Vicinity of SFO...VFR. Low to mid level clouds increase tonight
and Wednesday with showers and a few thunderstorms. Showers and
thunderstorms may produce briefly gusty winds and heavy rain.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR-MVFR. Low to mid level clouds
increasing tonight and Wednesday with showers and a few
thunderstorms. Showers and thunderstorms may produce briefly gusty
winds and heavy rain. With the cold core low over the north
Central Coast Wednesday night and Thursday morning expect
additional heavy showers and thunderstorms Wednesday night and
early Thursday morning.
&&
.MARINE...
(Tonight through next Monday)
Issued at 953 PM PDT Tue Sep 23 2025
Widely scattered to scattered rain showers and thunderstorms will
arrive over the southern coastal waters late tonight. Showers and
thunderstorms will steadily move northward across the waters and
bays through Wednesday. Thunderstorms will pose the risk of gusty
outflow winds, locally rough seas and locally very heavy rain.
Winds increase to a fresh breeze by the end of the week. Moderate
seas will prevail through Wednesday, building to become rough in
the outer waters Thursday into Friday.
&&
.FIRE WEATHER...
Issued at 932 AM PDT Tue Sep 23 2025
Warm and dry weather today will be followed by a chance for
thunderstorms overnight and continuing through the day Wednesday.
While the Central Coast is expecting a good amount of wetting
rain showers to accompany any lightning, it looks much drier
further north. There is still enough instability to trigger some
thunderstorms across the central and North Bay Wednesday, bringing
a slight chance for dry lightning to those areas on Wednesday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Canepa
MARINE...Canepa
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NWS MTR Office Area Forecast Discussion