Bloomfield, California Weather Forecast Discussion

797
FXUS66 KMTR 090928
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
228 AM PDT Tue Sep 9 2025
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 220 AM PDT Tue Sep 9 2025
- Slight (15%) chance for thunderstorms during the afternoons
   through Thursday
- Below normal temperatures and rain shower chances will continue
   through Thursday
&&
.SHORT TERM...
Issued at 220 AM PDT Tue Sep 9 2025
(Today through Thursday)
While it`s not technically Water Year 2026 yet (October 1st, 2025),
the "first rain of the season" is underway via a cold front. The
parent feature is a cold and moist upper-level low as noted by the
September 9th 00Z balloon. It recorded a 1.24 inch precipitable
water value which is the second highest for this date and time (1.37
inches in 1998) and an 850 millibar temperature of 11.95 degrees
Celsius which is near the 10th percentile (11.8 degrees Celsius).
While the cold air aloft is notable for this time of year, well
below normal temperatures at the surface will likely do little to
capitalize on the situation i.e. the atmosphere will be less
inclined to "flip" cool air over cold air than hot air over cold
air. Still, there`s a slight (15%) chance for thunderstorms during
the afternoons of today, tomorrow, and Thursday as the essential
ingredients of lift, instability, and moisture will be there. The
best chance for timing will be Wednesday afternoon as the core of
the upper-level low will be over our area. The best chance for
location will be the North Bay (namely northern Napa and Sonoma
Counties) where most unstable convective available potential energy
(MUCAPE) (in this case it will be surface based) will reach
approximately 500 Joules/kilogram. With the exception of orographic
lift induced thunderstorms, maximum temperatures will be the
limiting factor as model point soundings illustrate a long, skinny
CAPE profile. Lightning/flooding threats exist with all
thunderstorms: when thunder roars, go indoors! and see a flash, dash
inside! Outside of thunderstorms, rain showers will be beneficial.
&&
.LONG TERM...
Issued at 220 AM PDT Tue Sep 9 2025
(Friday through Monday)
Global ensemble clusters suggest it is likely that the upper-level
low will exit to the northeast Friday, raising heights and
temperatures at least briefly. Troughing returns to the West Coast
Sunday with another cold front and light rainfall chances.
&&
.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...Sarment
LONG TERM....Sarment
AVIATION...JM
MARINE...JM
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NWS MTR Office Area Forecast Discussion