Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
406 PM PST Friday Dec 26 2014
..much cooler temperatures expected tonight with wide spread frost
expected for inland locations...
Synopsis...cold temperatures expected once again tonight
into Saturday morning. These cold temperatures will result in wide
spread frost for many inland locations and a freeze warning for
portions of Monterey and San Benito counties. Otherwise...dry
weather is expected to persist into the beginning of next week
with cold overnight temperatures possible once again by middle week.
Discussion...as of 2:20 PM PST Friday...the current visible
satellite image is showing clear skies around the entire forecast
area. Local observations are indicating light offshore winds with
a few stronger wind observations in the San Francisco Delta area
reaching 23 miles per hour. Although...skies were clear and sunny all day
temperatures have only reached into the middle 50s to upper 50s this
afternoon with San Rafael reporting 61 degrees at this hour. This
suggests that the cold airmass remains in place over the San
Francisco and Monterey Bay area.
With the cold airmass in place and light offshore winds overnight
expect another cold night around the area. Overnight lows are
expected to be in the low to middle 30s at many inland locations with
upper 20s anticipated for southern Monterey and San Benito
counties. San Francisco Bay area overnight temperatures are
expected to remain in the upper 40s to lower 30s. As previously
mentioned our frost advisory criteria does not permit US to issue
a frost advisory for non urban areas after December 15th.
However...due to the cold crisp airmass expect wide spread frost
to develop at many locations overnight tonight. Additionally...a
freeze warning has been issued for portions of Monterey and San
Benito counties due to the cooler temperatures expected in those
The 1200z European model (ecmwf) along with the 1800z gfs40 and nam12 have
initialized well with the current synoptic pattern and remain in
good agreement through the next 84 hours. The forecast models are
suggesting another cold night tonight before the airmass modifies
permitting slightly warmer temperatures for Saturday night into
In the extended forecast both the 1200z European model (ecmwf) and 1800z gfs40
continue to forecast a cold storm system pushing into the Great
Basin states on Sunday. This cold storm system slides into
northern and central California during the Monday night...Tuesday
morning time frame. Although the forecast models are coming into
closer agreement some disagreement remains with the exact timing
and trajectory of this storm system. Depending on the track of the
system our area could be in for another round of cold temperatures
by middle week with a possibility of snow showers in the hills. We
will continue to keep an eye on this developing weather story as
Aviation...as of 4:00 PM PST Friday...a cool dry airmass will
remain over the region providing clear skies across area
terminals. Light winds will persist through the forecast period.
Vicinity of ksfo...VFR.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
Marine...as of 1:57 PM PST Friday...strengthening high pressure
will result in diminishing north to northwest winds through the
remainder of the day. Winds turn light early tomorrow morning and
veer east. Breezy north winds return Sunday night. Northwest swell
will prevail through the next several days with a moderate wind
wave component early next week.
... Warning...southern Salinas valley...Santa Lucia
mountains and Los Padres National Forest-
mountains of San Benito and interior
Monterey County including Pinnacles np
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm until 9 PM
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm until 9 PM
Public forecast: Larry
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