Bloomfield, California Weather Forecast Discussion

576
FXUS66 KMTR 110437
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
937 PM PDT Wed Sep 10 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 201 PM PDT Wed Sep 10 2025
- Unsettled weather continues into Thursday
- Drier and slightly warmer weather Friday and Saturday.
- Unsettled weather may return to the Bay Area on Sunday.
&&
.UPDATE...
Issued at 703 PM PDT Wed Sep 10 2025
Rain shower and thunderstorm activity is on the downtrend as
daytime heating is lost. Over the past six hours, accumulations
range from 0.01" to 0.48" - fortunately most of this was
beneficial rain. Looking ahead to tomorrow, there`s still a chance
for thunderstorms, but it`ll be less favorable as the longwave
trough slowly weakens and exits east. The greatest chances are
once again in northern portions of Napa and Sonoma Counties.
Sarment
&&
.SHORT TERM...
Issued at 201 PM PDT Wed Sep 10 2025
(This evening through Thursday)
It is shaping up to be a fairly active afternoon across the North
Bay with scattered convection across the northern parts of Sonoma
and Napa Counties. A deep upper level low hovers over northern
California, cooling the upper atmosphere and providing enough
buoyancy to fuel convective activity, assuming a source of moisture
and lift. A special 18Z (11 AM) sounding from Oakland showed surface-
based CAPE values of around 187 J/kg (near seasonal maximum record
values, with model output showing higher values across the North
Bay) , and 1.19" of precipitable water (above the 90th percentile of
the seasonal distribution of precipitable water values), with
lifting forces generated by topographic forces and a trough centered
in the northern Central Valley. These factors combine to give us a
20-35% chance of thunderstorms in much of Sonoma and Napa Counties
this afternoon and evening, with the chances diminishing later in
the evening as solar heating decreases and ends.
The KDAX radar is showing the bulk of the convection just to the
north in Lake County into the northern coastal ranges. Within the
past hour, lightning has been reported with the cells in Lake
County. The main concerns should these cells edge into northern
Sonoma and Napa counties are localized heavy rainfall, lightning,
and gusty winds. The possibility of a severe cell migrating over the
the Pickett Fire burn scar is of particular concern, as areas within
the burn scar will be more susceptible to debris flows or mudflows.
We will continue to monitor activity near the Pickett Fire, and
across the North Bay, through the rest of the evening. Remember:
When thunder roars, go indoors! Or, see a flash, dash inside!
KMUX radar data has been intermittent due to communications issues,
but what data does make it through suggests that a second
concentration of shower activity exists from southern San Mateo and
western Santa Clara Counties, into Santa Cruz County and off the
coast of the Monterey Bay region. These showers are strictly
convective, that is, driven by processes of atmospheric lift
(assisted by the Santa Cruz Mountains), but we`re not expecting the
same level of concern in regards to gusty winds or debris flows.
This is the type of shower activity that we expect for the rest of
the Bay Area and Central Coast, although we will note that there is
around a 5-10% chance of thunderstorms in the Bay Area and Monterey
Bay region.
Drier conditions are expected on Thursday, although a lingering
chance for showers persists in the North Bay along with a very
slight chance (up to 10% probability) of thunderstorms in the
northern reaches. Today`s highs reach the lower to middle 70s inland
and the middle 60s to lower 70s along the coast, with Thursday`s
highs warming to the middle 70s to lower 80s inland with coastal
highs similar to today`s.
&&
.LONG TERM...
Issued at 201 PM PDT Wed Sep 10 2025
(Thursday night through next Tuesday)
A brief period of ridging settles in for Friday and Saturday, with
dry conditions and temperatures reaching the upper 70s to middle 80s
inland, perhaps into the lower 90s in the warmest spots of Monterey
County. Another cold front approaches the region on Sunday, bringing
a few degrees of inland cooling and a slight chance (15-30%
probability) at some drizzle to light rain in the North Bay. Beyond
that, the forecast becomes even more uncertain, with careful
analysis of the ensemble model cluster analysis suggesting an
approximately even split between weak troughs or cutoff lows over
the West Coast, or weak ridges over the western US. CPC outlooks are
leaning towards temperatures above seasonal averages heading into
the last week of September.
&&
.AVIATION...
(06Z TAFS)
Issued at 916 PM PDT Wed Sep 10 2025
Showers have ended as the marine layer starts to reorganize
tonight. As the atmospheric stability returns in the low levels,
cumulus clouds will transform into a more uniform stratus layer.
While the cloud coverage will be more extensive than last night,
there is still enough mixing in the deep boundary layer to keep
ceilings in the MVFR category for all terminals through the night.
Vicinity of SFO...Fairly high confidence in MVFR ceilings through
the night, although there is a 25% chance for IFR conditions to
sneak in sometime before 18Z. While some guidance is actually
suggesting ceilings will persist through the day tomorrow, the
TAFs are more optimistic with VFR conditions in the afternoon and
early evening. Based on the ceiling height, drying trend, and
compressing marine layer, this seems more reasonable. Otherwise
moderate westerly winds are expected for a few hours in the
afternoon before decreasing in the evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...A pocket of dry air approaching the coast
makes the short term forecast a little tricky. The well
established ceilings may break for a couple hours before
returning around midnight. Fairly high confidence in a clearing
trend from late morning through the afternoon before ceilings
return Thursday evening and the pattern returns to the typical
marine layer set-up.
&&
.MARINE...
(Tonight through next Tuesday)
Issued at 916 PM PDT Wed Sep 10 2025
Buoy and satellite data confirm gentle to moderate NW winds and
moderate sea heights across the coastal waters. Similar
conditions will persist through Thursday before stronger NW winds
and rough seas arrive early Friday. Conditions will briefly
improve Saturday before fresh to strong northerly winds return
late Sunday, rebuilding rough seas in the northern waters.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 PM Thursday to 3 AM PDT Saturday for
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-
     Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras
     Blancas 0-10 nm.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Flynn
MARINE...Flynn
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NWS MTR Office Area Forecast Discussion