Bloomfield, California Weather Forecast Discussion

532
FXUS66 KMTR 091213
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
513 AM PDT Tue Sep 9 2025
...New AVIATION, MARINE...
.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...
(12Z TAFS)
Issued at 513 AM PDT Tue Sep 9 2025
Scattered showers will continue to impact airports across the Bay
Area and Central Coast through the remainder of the TAF period.
Highest confidence in showers this morning and again late this
afternoon/overnight. 10% chance of thunderstorms across the North
Bay this afternoon and 5% chance of thunderstorms across rest of Bay
Area. Confidence was too low to include thunderstorms in TAF at this
moment but will need to keep an eye on radar and potentially amend
TAFs later today. Thunderstorm chances look to be better on
Wednesday than on Tuesday. Moderate confidence in CIGs remaining
MVFR through late this morning with CIGs rising/VFR conditions
returning late morning/early afternoon. CIGs lower late this evening
into the overnight hours as the next round of showers reaches the
region.
Vicinity of SFO...Scattered showers and MVFR conditions impact SFO
for the majority of the TAF period. Moderate confidence that CIGs
will rise by early this afternoon before MVFR conditions return late
this evening. There is a 5% chance of thunderstorms impacting SFO
this afternoon with confidence too low to include TS in TAF. MVFR
conditions and scattered showers return late this evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Primarily MVFR conditions through late
morning/early afternoon. Temporary IFR CIGs have developed at MRY
and SNS early this morning and will continue to periodically move
through this morning as showers impact the area. Scattered light
showers are expected this morning and again this evening/overnight.
Current thinking is that CIGs will be on the MVFR/IFR border tonight
with slightly higher confidence in IFR CIGs impacting MRY tonight.
&&
.MARINE...
(Today through Sunday)
Issued at 513 AM PDT Tue Sep 9 2025
Scattered light rain showers are expected across the coastal
waters  Tuesday through Thursday as an upper level low moves into
the West  Coast. Isolated thunderstorms are possible during the
afternoon  Tuesday through Thursday. Thunderstorm chances peak on
Tuesday  across the northern coastal waters. A gentle to moderate
breeze will  continue Tuesday with a moderate to fresh breeze
developing over the  outer waters Wednesday into the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Kennedy
MARINE...Kennedy
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NWS MTR Office Area Forecast Discussion