881
FXUS66 KMTR 092141
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
241 PM PDT Sun Mar 9 2025

...New SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 313 AM PDT Sun Mar 9 2025

Pleasant weather today, under mostly sunny skies. Cooling trend sets
in Monday with increasing rain chances beginning late Tuesday night.
Gusty winds and periods of heavy rainfall are expected Wednesday
with high surf conditions persisting into Thursday. Another
disturbance will bring more widespread rainfall next weekend.

&&

.SHORT TERM...
Issued at 215 PM PDT Sun Mar 9 2025
(This afternoon through Monday)

Wall to wall sunshine blanket the Bay Area and Central Coast this
afternoon. After a chilly start to the day the abundant sunshine
and insolation has led to a nice end to the weekend. Temperatures
this afternoon will top out in the in the upper 50s to near 70.

The broader picture over the Epac reveals an active pattern
shaping up. A highly amplified split flow is currently taking am
at the West Coast. The split flow shows the subtropical jet near
Hawaii streaming right into Baja. Just north of that is the high
amplified polar jet with a jet max near the Aleutians, which is
diving south toward the subtropical jet just off the CA coast. The
digging jet almost phases with the southern jet, but doesn`t
quiet happen. Regardless, at the base of the digging trough is a
low spinning off the CA coast. One can actually see the low
spinning on vis satellite.

Tonight and Monday: The low spinning off the coast will inch its
way eastward tonight and ultimately move inland over SoCal. The
passing low will bring a slight increase in mid-high level clouds
tonight and tomorrow. Additionally, there is a very low chance
20%) of light precip skirting the Central Coast. The rest of the
Bay Area will remain dry. Another cool night on tap, but not as
cold as this morning due to some higher clouds. Temperatures on
Monday will remain mild and similar to Sunday. SoCal has a better
shot at seeing precip than our forecast area.

&&

.LONG TERM...
Issued at 230 PM PDT Sun Mar 9 2025
(Monday night through next Saturday)

Another amplification of the polar jet carves another trough off
the West Coast Monday into Tuesday. This trough will lead to
cyclogenesis with a frontal system sweeping through the region.
The warm sector of this system will spread light rain into the
North Bay Tuesday evening/night before getting a kick front the
cold front on Wednesday. The morning commute on Wednesday would be
problematic with wet roads and increasing rain
coverage/intensity. As the day progresses on Wednesday the cold
front does tap into better moisture. The PWAT plume does extend
back to Hawaii, but it is discontinuous. That being said, PWAT
will hover on either side of 1". Therefore, calling this a weak AR
seem appropriate. The moisture rich air will flow perpendicular
to the coast leading to orographic enhancement and some inland
rain shadowing. The passing front on Wednesday will also bring an
abrupt change with a plummeting 700 and 500 mb temps with a sub
540DAM 1000-500mb thickness. As such, snow levels will drop late
Wednesday into Thursday (2,500-3,000 feet). Therefore, some snow
will be possible over the higher peaks of the Bay Area and Central
Coast. Additionally, the change in airmass will lead to increased
instability Wednesday night and Thursday. Sfc CAPE, MUCAPE, Lapse
rates, and LIs all indicate a chance for thunderstorms. Given the
thermal profile small hail will be possible on Thursday as well.
Lets talk precip totals as the system winds down late Thursday.
Rainfall: N Bay Mts and all Coastal Mts 2-3 inches and locally up
to 4" above Big Sur with 0.75-1.5" elsewhere around the region.
Snowfall - little to no accumulation N and E Bay with a six inches
possible in the Santa Lucia Mts.

Two other impacts in addition to precip will be wind and
temperatures. Winds will increase out of the south on Wednesday
and remain gusty with the fropa. Not strong enough for a wind
advisory at this time, but windy nonetheless. Overnight lows
will be cold Thursday night into Friday with frost advisory
potential across the interior.

After the very brief break late Thursday widespread precip returns
Friday and next weekend. Another weak AR takes aim at the Bay Area
with more rain. Early estimates show similar rainfall totals as
the midweek system.


&&

.AVIATION...
(18Z TAFS)
Issued at 1022 AM PDT Sun Mar 9 2025

VFR expected for all terminals except Half Moon Bay. Onshore flow,
ample low level moisture, and sea spray will result in
occasional MVFR conditions. KSTS and KMRY has a 20-30% chance of
see some low clouds or patchy fog late tonight and early Monday,
but think increase mid to high level clouds will limit
development.

Vicinity of SFO...VFR. Onshore flow today and most of tonight.
Winds to SE and eventually NE early Monday. Despite wind switch,
speeds should be light to moderate.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR conditions. Will need to keep an eye
on KMRY late tonight as some guidance suggests a low chance for
some cigs.

&&

.MARINE...
(Today through Friday)
Issued at 823 AM PDT Sun Mar 9 2025

Seas and winds will remain moderate through Tuesday. Hazardous
conditions return Wednesday in the form of rough to very rough
seas, a strong southwesterly breeze with gale force gusts, and
moderate rainfall with a slight chance for thunderstorms Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...MM
MARINE...Sarment

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