Hello, I am Warning Coordination Meteorologist
Logan Johnson at the National Weather Service office, San Francisco Bay Area, located in
Monterey California. This is a high impact weather briefing for the arrival of a series
of Pacific Storms expected to impact the San Francisco and Monterey Bay areas. Please do
not use the information contained here after noon on Wednesday, November 28, 2012 as it
will be subject to change. The series of upcoming storm systems will
produce high impact weather. A strong Pacific Low pressure will move towards the area and
bring a series of storm systems with significant rainfall over a few days which will produce
flooding concerns by this weekend. Winds will also increase late tonight from the south
as the storm approaches and will be strong enough to produce some damage. And isolated
thunderstorms will accompany the storm system as it approaches tonight and Wednesday. These
will be the greatest impacts and we will take a look at these in a little more detail.
Significant rainfall is expected across the Bay Area over the next several days from a
series of storm systems. Rainfall amounts will be heaviest in the high terrain and in
the North Bay. Rainfall in excess of 12 inches over the next several days is possible in
the favored westward facing slopes of high terrain. Important to note is the timing of
the three storm systems. In between these three storms, only lighter rainfall is expected.
The most significant rain will fall during these three storm systems. Lower elevations
will see lower rainfall totals but still several inches are expected. The lightest rain is
expected in southeastern Monterey and San Benito counties of 1 to 3 inches.
With the significant rainfall there will be flooding concerns as well. Small creeks and
streams are expected to flood in favored locations especially in the higher elevation. Rising
water levels can be expected on large rivers especially in the North Bay like the Russian
and Napa Rivers. The graphic here shows a forecast for the Russian River and the rises
expected there. The pink line to the right shows the expected increase in the water level
on the river. Note that while it rises quickly, the current prediction is for the river to
remain below flood stage. Additional Urban flooding issues will be enhanced and complicated
by tree debris like leaves and small branches that fall and clog storm drains. There is
also a potential for landslides in the high terrain as the ground becomes saturated on
hillsides. South winds will increase late tonight and
into Wednesday. Winds will be strongest over the waters and near the coast. High elevations
will see strong winds as well. Winds will be a bit lighter across the inland valleys
of the area especially in the Santa Clara Valley and into Monterey and San Benito counties
in the southern part of the area. Gusts of 65 MPH on the coast and along the ridge tops
will be possible and these can produce damage to downed trees and power lines. The highest
wind gusts will come on Wednesday morning. Visit the link shown here for more information.
Marine impacts will be significant this week with the storm systems. Increasing winds by
late tonight will reach Gale Force at 35 to 40 knots with gusts to 50 knots. All of the
local Pacific waters as well as the San Francisco and Monterey Bay waters will be in a Gale
Warning for late tonight and Wednesday. Also a hazard will be high seas in the Pacific
with the strong winds producing seas of 14 to 18 feet well offshore.
Thunderstorms will accompany the first storm system moving in late Tuesday night and Wednesday.
Storms can produce lightning and gusty winds across the area which could enhance the damaging
wind threat where storms do develop. Widespread severe weather is not expected.
The next scheduled update will be on Wednesday as more information and more accurate details
will be available then. Unscheduled updates can occur if significant changes are expected
to the forecast impacts. In the meantime you can follow the San Francisco Bay Area National
Weather Service on twitter @nwsbayarea. You can also follow us on Facebook and the easiest
way is to search for the US National Weather Service San Francisco. And you can always
visit on the web at weather.gov/sanfrancisco. Please share your feedback and as the storm
arrives we would love to hear how its impacting you, and your rainfall amounts and wind gusts.
Thank you for watching.