918
FXUS66 KMTR 050550
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
950 PM PST Tue Feb 4 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1202 AM PST Tue Feb 4 2025

An atmospheric river will continue to bring heavy rain, urban and
river flooding, and strong winds to the Bay Area and Central
Coast through Tuesday. There is also an increasing chance for
thunderstorms in the afternoon. While less impactful in the
second half of the week, rain chances continue through Friday.

&&

.SHORT TERM...
Issued at 215 PM PST Tue Feb 4 2025
(This evening through Wednesday)

Key Points:
* Flood Advisories and Flood Warnings continues for portions of
  the Bay Area
* Flood Watch remains effect through 4 AM Wednesday across the
  Bay Area and Central Coast
* Dynamic afternoon/evening as a cold front brings heavy rain,
  very gusty winds, and possible thunderstorms
* Post frontal cold temperatures tonight- N Bay Valley Frost
  Advisory
* Thur-Fri AR will bring another round of rain with re-newed
  flooding concerns
* Cold morning temperatures return mid-week but temperatures
  will drop more significantly over the weekend

Afternoon/evening - The much anticipated surface low, associated
cold front, and accompanying upper level jet max are making their
presence known. Since this morning, radar has become much more
active with a line intermixed with cells showing up along the
approaching cold front. The wind field ahead of the front has also
ramped up with a few coastal sites showing gusts 65-85 mph. A
special balloon sounding was launched from OAK at 20z to further
analyze the atmospheric profile, especially the wind profile. The
biggest concerns this afternoon - low CAPE high shear environment
will lead to convectively driven wind and possible spin ups with
any stronger cell. Given the juicy atmosphere, any stronger cell
has some decent rainfall associated with it - 0.5-0.75" per hour.
Those rates on already wet soil/full creeks/streams will add
additional flooding concerns. Simply put, make sure you have ways
to receive weather alerts whether it`s for severe or flooding.
Also, allow for extra time during the evening as heavy rain will
impact the commute. Do not drive through flooded roadways.

Tonight into Wednesday: Conditions will gradually improve as the
cold front pushes through the forecast area. Convective rain from
the evening will transition to scattered showers N to S. While
precip gradually diminishes in coverage and intensity flooding
concerns will remain due to full creeks/streams. Winds will also
decrease behind the front. Some chilly air is expected to fill in
behind the front with decreasing winds and clearing skies. As
such, a Frost Advisory has been issued to capture temperatures
reaching the low to mid 30s for the Sonoma Valley specifically.
Even if the clouds linger longer and temperatures remain in the
mid to upper 30s it will feel cold given the damp conditions.
Wednesday will be a reprieve as one system exits and another
approaches from the west. Given the colder air aloft and upstream
upper level trough widely scattered showers will be possible.

&&

.LONG TERM...
Issued at 245 PM PST Tue Feb 4 2025
(Wednesday night through next Monday)

Wednesday night will be a low confidence higher impact potential
forecast. A lot will depend up cloud cover and impacts for
overnight lows. For now, current forecast is trending colder with
widespread 30s to near 40 and interior Central Coast near
freezing. A Frost Advisory may bee needed.

Thursday and Friday...another AR is still on track with more
moisture taking aim at the region. Thankfully this AR looks much
weaker with less of a deep moisture tap. Expect shower coverage to
increase through the day on Thursday and linger into Friday.
Despite a weaker system flooding concerns will remain given how
much rain has fallen over the last 24 hours. Rainfall amounts are
generally expected to be 0.25-1.00" and 1.5" coastal mts. As
precip begins to taper off on Friday colder air begins to move in
from the north lowering snow levels. Some wet snow will be
possible over the higher terrain.

Drier weather finally returns over the weekend. The weather
impacts quickly turns toward cold overnight lows. We`re talking
widespread 30s with interior in the mid to upper 20s. Frost and
Freeze products will likely be needed.

&&

.AVIATION...
(06Z TAFS)
Issued at 949 PM PST Tue Feb 4 2025

CIGs continue to lift in the post frontal environment leading to
widespread VFR in the late night for all but the North Bay which will
see some pockets of fog and mist. Additional showers move through the
region in the late night through the morning for the SF Bay and
North Bay Terminals. Moderate winds turn light overnight and become
moderate again into Wednesday afternoon then light again that night.


Vicinity of SFO...VFR through the TAF period. Expect gusty winds to
east overnight and become light into early Wednesday. Showers pass
through the area in the early morning but exit by the late morning.
Moderate west winds arrive for Wednesday afternoon but become light
and variable that night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...CIGs lift into the late night with moderate
winds weakening into Wednesday morning. Moderate west winds arrive
Wednesday afternoon before weakening that evening.


&&

.MARINE...
(Tonight through next Monday)
Issued at 949 PM PST Tue Feb 4 2025

Showers and storms are exiting as winds begin to ease. Lingering
gusty winds will cause hazardous conditions for small craft into
early Wednesday for much of the waters, but will subside through
the rest of the morning.  Another storm system will impact the
coastal waters Thursday into Friday with increasing winds and
rain.

&&

.HYDROLOGY... Issued at 1200 PM PST Tue Feb 4 2025

A moisture rich atmospheric river and accompanying surface low is
bringing widespread rainfall across the Bay Area and Central
Coast. Already primed soils and higher rain rates will maintain
an increased potential for flooding across the North Bay and
coastal ranges today into Wednesday. CNRFC has increased
forecasted river stages across several rivers and streams in
response to higher forecasted precipitation. The latest main stem
river forecast has the Russian River at Johnsons Beach at
Guernville (GUEC1) rising to Action Stage (29 ft) this evening and
into Minor Flood Stage (32 ft) overnight. A Flood Warning is in
effect for this location beginning at 1 AM tonight. In Napa County
the Napa River at St Helena is forecast to rise into Action Stage
(16 ft) this afternoon and the Napa River near Napa is forecast
to rise into Action Stage (22 ft) tonight.

Other non-main stem forecast points that are currently under a
Flood Warning include...

GEYC1 - Russian River at Geyserville is currently in Minor Flood
(>39.7 ft) and forecast to remain in Minor Flood through tonight.

MWEC1 - Mark West Creek at Mirabel Heights is currently in Minor
Flood (>55 ft) and continuing to rise. It is expected to reach
Moderate Flood (>59 ft) later this afternoon.

GRQC1 - Green Valley Creek at Martinelli Road is currently in
Moderate Flood (>63 ft) and rising.

CTIC1- Laguna de Santa Rosa at Stony Point Road near Cotati is
currently in Minor Flood (>84 ft) and continuing to rise. It is
expected to reach Moderate Flood (>85 ft) in the next few hours.

 These locations will be handled through ongoing Flood
Advisories.

A Flood Watch will remain in effect through late tonight.
Several Flood Advisories are in effect this afternoon with
numerous reports of urban and small stream flooding across the
northern half of the Bay Area.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Frost Advisory until 9 AM PST Wednesday for CAZ506.

PZ...Small Craft Advisory until 3 AM PST Wednesday for Mry Bay-Pigeon
     Pt to Pt Pinos 0-10 nm-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
     Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge.

     Small Craft Advisory until 9 PM PST Wednesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...Murdock
MARINE...Murdock

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