Spotters self-activate; Rain next several days throughout the area

SF Bay Area Skywarn spotters in the North Bay should self-activate immediately. Spotters in the rest of the Bay Area should self-activate starting Monday afternoon / evening.

Flood Watch until February 2, 10:00 PM PST

Rain will continue throughout the Bay Area at least through Tuesday night. The North Bay will be mostly impacted through Sunday. Starting Monday and lasting at least through Tuesday night, the entire Bay Area will get significant rain and winds.

The SJSU WRF 2KM Ensemble Precipitation Forecast 12Z run on Feb 1 shows a rapid increase in the ensemble mean at approx midnight on Monday night / Tuesday morning at KSJC, which indicates a later start to the heavy rain in the South Bay, whereas at KSFO the increase starts in the early to mid afternoon.

This graphic shows the model ensemble 6-hour precip forecast intensifying over the Bay Area during the afternoon (4pm) on Monday Feb 3.

From MTR AFD:

.LONG TERM...
(Sunday through Friday)
Issued at 317 AM PST Sat Feb 1 2025

Showers are expected to continue through the remainder of the
weekend and into next week as an AR continues to impact the West
Coast. Sunday will act as a brief break between rounds of heavier
rainfall on Saturday and Monday with lighter rain expected
everywhere. After the passage of Saturday`s shortwave trough, the
upper level flow becomes more zonal (reducing upper level forcing)
and the surface low pressure system shifts northward, becoming
stationary over the North Bay. This will shift the moisture plume
northward as well and continue to train moisture over the North Bay
with locally higher rainfall totals possible there. Comparatively,
the amount of available moisture will be reduced farther south, with
fairly light rain totals anticipated outside of the North Bay. Given
this, an additional 1"-2" of rain is possible over the North Bay, up
to 1" across the Bay Area, and up to 0.25" across the Central Coast
on Sunday.

Heading into Monday, zonal flow will give way to persistent upper
level troughing across the West Coast, kicking off the next round of
moderate rain. The surface low pressure system will become less
stationary as the upper level trough develops with the associated
moisture plume widening and spreading southwards on Monday. A cold
front associated with this low will progress through the Bay Area
and Central Coast late Monday night into Tuesday morning. This
system will bring an additional 2"-4" of rain to the North Bay, 1"-
2" to the rest of the Bay Area, up to 3" across the Santa Cruz
Mountains and Santa Lucia Range, and 1"-2" across the Central Coast.
At the same time, cold frontal passage will increase atmospheric
instability and bring a 10-20% chance of isolated thunderstorms over
the coastal waters and along the coastline Tuesday morning.
Thunderstorm chances will peak early Tuesday morning before
decreasing through the remainder of the day.

Additional rounds of light rain (generally totaling to between 0.5"-
1.0") are expected Wednesday through Friday as persistent upper
level troughing continues over the West Coast. Gusty winds persist
throughout the week with cooler morning temperatures returning
Wednesday through the extended forecast. The combination of gusty
winds, cold mornings, and continued wet weather will create
hazardous conditions for those without adequate access to heat or
shelter. Cold weather products are likely to be evaluated for mid
week and beyond as we get closer in time to them. For snow lovers,
it is worth noting that, in the wake of cold frontal passage, snow
levels will drop to between 2500-3500 feet for portions of the
region. This, in combination with the continued wet weather,
means there is a non- zero chance for light snowfall on the
highest peaks of the North Bay Mountains and in the Santa Lucia
Range. While confidence remains low, probabilistic guidance does
show a 30-40% chance of trace snowfall across the peaks of the
North Bay Mountain mid to late week. This is still several days
out and the forecast is likely to change, but, it may be worth
keeping an eye on the Cal Alert Cameras late week to see if you
can spot any mountain snowfall.