Villa Grande, California Weather Forecast Discussion

398
FXUS66 KMTR 090510
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1010 PM PDT Mon Sep 8 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 210 PM PDT Mon Sep 8 2025
- Chance for light rain this afternoon through Tuesday.
- Showers linger Wednesday and Thursday, dry early into the weekend.
- Below normal temperatures this week.
&&
.UPDATE...
Issued at 642 PM PDT Mon Sep 8 2025
The 00Z balloon for September 9th recorded a 1.24 inch
precipitable water value - this is the second highest value for
this date and time (highest is 1.37 inches in 1998). The culprit
is a low pressure system off the California Coast that will bring
us unsettled weather through Thursday. Light rain has begun in
the North Bay with only two sites picking up 0.01" so far. No
updates needed to the forecast in the interim.
&&
.SHORT TERM...
Issued at 210 PM PDT Mon Sep 8 2025
(This evening through Tuesday)
An upper level low pressure system is currently spinning off the
coast of NW CA this afternoon as depicted by water vapor satellite
imagery. Radar has been fairly quiet on our end, with a few echos
traversing our northern portion of the coastal waters. Expect this
slower trend to continue, with showers potentially creeping into
Sonoma County`s coast over the next several hours, but more likely
closer to this evening. What does that mean for the rest of us? The
onset of rain continues to be delayed, likely not reaching areas
until tonight or after midnight. By tomorrow afternoon, post front,
we`ll have additional chances for showers. The question will be if
we get enough forcing for thunderstorms. We have ingredients for
them; however, this will likely be depending on if they can all line
up. Guidance shows we might have 100-300 J/kg of MUCAPE, moisture,
and weak, if any, shear of around 10-30kt. Lapse rates aren`t
looking quite as impressive with the morning models, thus expect
cumulus, some showers and maybe a rumble of thunder. Any
thunderstorms that do develop should have some rain associated with
them. The best chances for rain continue to be over the North Bay
counties, where we could see anywhere from a couple hundredths of
an inch to 0.15" through Tuesday evening. Elsewhere, we might
squeak out a few couple hundredths of an inch.
&&
.LONG TERM...
Issued at 210 PM PDT Mon Sep 8 2025
(Tuesday night through next Sunday)
Forecast remains rather cool and slightly unsettled as the upper
level low will slowly track east across N CA. Unseasonably cool
temperatures, the potential for afternoon showers will be possible
Wednesday and Thursday. Parameters continue to remain limited for
thunder, but currently favor the northern portions of Sonoma and
Napa counties over the terrain. The NAM and some CAMs try to hint
at some convection down the Diablo Range and into interior San
Benito/Monterey counties. Confidence remains low for those areas
at this time, thus opted to keep thunder confined to the north for
now.
Once the trough exits the region, a quick bout of ridging moves into
the region. This will bring an increase in temperatures Friday into
Saturday. Ensembles beyond this period struggles with the timing of
the next penitential trough. Opted to keep PoP in for Saturday
into Sunday, with a slight downward trend in temperatures.
&&
.AVIATION...
(06Z TAFS)
Issued at 948 PM PDT Mon Sep 8 2025
Light rain has moved onshore into the North Bay this evening and
will continue to see off and on showers overnight and much of
Tuesday with little impact expected. An isolated thunderstorm will
be possible Tuesday afternoon, but chances are too low for
mentioning in the forecast. Light rain chances spread south by
early Tuesday morning, once again with impacts expected to be
minimal.
Vicinity of SFO...Periods of light rain are possible across the
Bay Area terminals late tonight through Tuesday morning, with
lingering showers Tuesday afternoon with little to no impacts
expected. An isolated thunderstorm is possible Tuesday afternoon,
however confidence is too low for mentioning in the forecast.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...MVFR ceilings are expected to persist
through Tuesday morning, with periods of light rain possible late
in the overnight period. Impacts from the rainfall are expected to
be minimal through Tuesday morning with VFR expected Tuesday
afternoon and early evening.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 449 PM PDT Mon Sep 8 2025
Gentle wind continue tonight with breezy conditions Tuesday
through Thursday. Moderate to fresh breezes anticipated over the
waters for the latter half of the week. Light rain beginning over
the northern waters this afternoon, continuing and spreading
southward into Tuesday morning. Scattered thunderstorms possible
during the afternoons Tuesday through Thursday, chances increase
with latitude.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...KR
LONG TERM....KR
AVIATION...JM
MARINE...JM
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NWS MTR Office Area Forecast Discussion