Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
954 PM PST Tuesday Nov 25 2014
Synopsis...dry weather and seasonably warm temperatures will
persist through Thanksgiving day as a result of high pressure over
the region. Unsettled weather will return to the North Bay as early
as Friday with rain slowly spreading southward through Saturday.
Widespread precipitation is then expected Sunday into Monday as a
stronger middle/upper level system pushes through the region.
Discussion...as of 8:59 PM PST Tuesday...mild weather and clear
skies will continue through Wednesday as high pressure overhead
maintains light offshore flow and above normal temperatures.
Travelers headed out of town will enjoy pleasant driving
conditions with no rain or fog expected over the San Francisco
and Monterey Bay area through Thanksgiving day.
The ridge of high pressure will begin to flatten Thursday as a low
pressure system approaching the West Coast moves into the Pacific
northwest coast. Rain chances are expected to begin over northern
California on Thursday then gradually spread south as the system
sags southward. Latest model runs bring rain into the North Bay
Friday night. Rain will spread south into the Bay area overnight.
The Monterey Bay region will likely see rain Saturday however
timing is still uncertain as models show the front stalling over
the Bay area Saturday then pushing through Saturday night as a
shortwave riding in on the longwave trough reaches the central
coast. While these two systems will bring well deserved rain to the
region mainly north of the Santa Cruz Mountains...a large low
pressure system taking aim at northern California will deliver the
knock out punch bringing significant rain to the entire warning
area on Sunday night into Monday. Models are in fair agreement
with the timing of this system and are expected to bring widespread
rain of moderate to locally heavy intensity to the region. Along
with rain this system will produce strong southerly winds Sunday
night into Monday as the frontal boundary moves across the region.
Travelers returning home over the weekend need to pay close
attention to the weather especially those returning home Sunday
night into Monday as they may encounter periods of heavy rain as
well as downed trees and power lines as a result of the winds.
From previous discussion...the middle/upper level trough axis will
then shift inland Monday night into Tuesday with lingering showers
possible across much of the region. While it remains very
difficult to predict rainfall totals at this point...it is Worth
mentioning that the GFS/ECMWF/CMC all show some portions of the
region receiving 3 to 5 inches of rainfall from Friday through
Monday night. The latest wpc 1-7 day forecast depicts 3 to 5
inches over the North Bay...2 to 3 inches across the Santa Cruz
Mountains and 2 to 2.5 inches for the satan Lucia mountains.
Meanwhile...inland areas could pick up anywhere from 1/2 inch in
the southern inland valleys to nearly 2 inches in the urban areas
of the San Francisco Bay area. Again...it is important not to
focus too much on these rainfall amounts at this time given the
expected fluctuations in the forecast models in the coming days.
Conditions dry out by the middle of next week with a ridge
building back across the region in wake of the exiting middle/upper
Aviation...as of 9:54 PM PST Tuesday...VFR is forecast for the
period except ksts may see fog early Wednesday morning. Light winds.
Vicinity of ksfo...VFR.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR.
Marine...as of 09:45 am PST Tuesday...high pressure will move
into the Great Basin tonight. Winds will become light east to
southeast by Wednesday as a frontal system moves into the Pacific
northwest. Southerly winds will increase by the end of the week as
a stronger storm approaches the area.
Public forecast: CW
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