Heaviest rain expected on Saturday and Monday

Friday’s storm will be mostly impacting the North Bay, but the whole Bay Area should expect some rain. Monday’s storm will likely be stronger across the entire Bay Area, and will include potentially heavy rain and strong westerly winds. This graphic shows precip forecast for Saturday 4pm PST according to the GFS model.

From MTR AFD:

.LONG TERM...
(Friday night through next Wednesday)
Issued at 248 PM PST Thu Jan 30 2025

Confidence continues to increase for widespread impactful rainfall to
persist through the remainder of the extended forecast. The first
system arrives on our doorstep late tonight. Much of the North Bay
will have already seen between 0.50-1.00" of rain by late tomorrow
night and early Saturday. The focus of higher rainfall amounts will
then shift south into the Bay Area, East Bay and Santa Cruz coastal
range throughout the day Saturday. A relatively strong upper level
trough axis will shift onshore late Friday into early Saturday when
increased rainfall rates can be expected from the North Bay into the
Bay area. While the parent low reconsolidates well to our north,
zonal flow with a series of embedded shortwaves will continue to
drive widespread light rain across most of our area, with enhanced
upsloping producing periods of moderate to heavy rain along our
coastal ranges through the weekend.

The main upper low then dives south late Sunday night into Monday.
Deterministic guidance is in decent agreement for the evolution of
the primary low`s shift south, but this part of the forecast will
continue to be watched closely. Any change or retreat north for the
beginning of next week, will result in big changes for rain totals
outside of the North Bay.

The rainfall totals for tonight through early Monday morning should
only lead to minor impacts with respect to flooding across the
North Bay. However, by the time the second round arrives for
Tuesday and Wednesday, we`ll see rivers and streams begin to
respond quicker to the steady fetch of rainfall expected. Even
with the higher end totals anticipated, there is roughly a 10%
chance of flooding for normal trouble spots along the Russian Rive
in Sonoma County and other locations into Napa County and Marin
County. As we monitor the rainfall this weekend, and the evolution
of the larger scale pattern for the beginning of next week, keep
an eye on subsequent forecast updates as these river forecasts
could change considerably. Along with the potential for periods of
moderate to heavy rain leading to flooding, there will also be
moderate to strong gusty winds. The strongest winds will be across
higher elevations, beginning Saturday morning with the passage of
the aforementioned trough axis moving onshore. As some might
expect, the strongest gusts should be expected over higher
elevations like Mt Helena, up to 60 MPH after sunrise Saturday
through much of the day. We`re anticipating the need for a Wind
Advisory beginning at some point early Saturday, with elevated
wind speeds continuing through the middle of next week. While
strong gusty winds at higher elevations may approach 60 MPH, lower
lying areas along the coast and inland valleys can expect max
wind gusts between 35-45 MPH at times.