Walnut Creek, California Weather Forecast Discussion

838
FXUS66 KMTR 082112
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
212 PM PDT Mon Sep 8 2025
...New SHORT TERM, LONG TERM...
.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...
(18Z TAFS)
Issued at 1024 AM PDT Mon Sep 8 2025
Slow to mix out this morning across the coastal and Bay Area
regions as deeper moisture moves in ahead of the approaching
trough. Will likely see some degree of clearing at most terminals
through midday and into this afternoon. Deeper clouds expected to
move in from north to south beginning late this afternoon as a
weak frontal system moves through. -SHRA will accompany the front
for North Bay terminals and most Bay Area locations with the
exception of terminals like KSJC and KLVK due to rain shadow.
Scattered showers anticipated to last well into Tuesday morning
(through the day for North Bay).
Vicinity of SFO...Slow to clear today, but VFR still anticipated
by the 20Z hour. -SHRA expected after midnight, but low confidence
in actually impacting the terminal due to sparse coverage through
the morning. Otherwise can expect MVFR cigs into Tuesday early
afternoon.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...IFR cigs with moderate confidence of VFR
timing this afternoon. Stratus will likely linger along coastal
areas well into the afternoon. -SHRA anticipated towards the
latter quarter of the TAF period beginning in the few hours before
sunrise across the Monterey Bay and Central Coast.
&&
.MARINE...
(Today through Saturday)
Issued at 444 AM PDT Mon Sep 8 2025
Winds increase to become fresh with breezy conditions Tuesday
through Thursday. Light rain is expected tonight into Tuesday
morning with convection possible during the afternoons of Tuesday
through Thursday, chances increase with latitude.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...KR
LONG TERM....KR
AVIATION...Behringer
MARINE...Canepa
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NWS MTR Office Area Forecast Discussion