Clayton, California Weather Forecast Discussion

684
FXUS66 KMTR 082351
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
451 PM PDT Mon Sep 8 2025
...New AVIATION, MARINE...
.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.
&&
.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...
(00Z TAFS)
Issued at 449 PM PDT Mon Sep 8 2025
A relatively weak surface cold front continues to approach our
area from offshore. The leading edge of the cold front is close to
shifting onshore north of KSTS and will arrive farther inland
near KSTS around sunset. Light showers and a slight chance of
thunderstorms will continue in vicinity of the slow moving front
later during the overnight into Tuesday morning for the remainder
of the Bay Area and Central Coast. Rain shadowing will result in
little to no rain for KSJC and KLVK through the TAF period. Light
rain chances will persist across the North Bay terminals most of
the day Tuesday.
Vicinity of SFO...Expect MVFR ceilings from late tonight through
early afternoon Tuesday with light rain at times. Expect VFR to
develop Tuesday afternoon and persist through the remainder of the
TAF period. There is less of a chance for light rain at KSJC and
KLVK due to rain shadowing effects from terrain.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Expect MVFR ceilings to fill in after
sunset with light rain expected by late into the overnight hours to
sunrise Tuesday morning. Light rain will linger in the vicinity of
Monterey Bay Tuesday morning with partial clearing and VFR
conditions Tuesday afternoon through the remainder of the TAF period.
&&
.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...Behringer
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NWS MTR Office Area Forecast Discussion