Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
857 PM PST sun Jan 25 2015
Synopsis...slight cooling is forecast for Monday as high pressure
over California weakens and moves to the east. A weak storm system
will move into Southern California on Monday night and bring a
chance of rain to the southern portion of our area on Monday night
and Tuesday...mainly areas south of San Jose. Dry and mild weather
is then forecast from Wednesday through the end of the week.
Discussion...as of 8:55 PM PST Sunday...slow clearing of fog/low
clouds across much of the sf Bay area today held temperatures
down for most Bay area locations. There was however a late day
upward surge in temperatures which managed to push richmond's high temperature
up to 69...enough to tie a record there. Farther south...from
Monterey Bay southward...the day started off sunny and
temperatures climbed quickly. Five locations around Monterey Bay
and in the Salinas valley set daily high temperature records this
afternoon...including an 84 degree high at the Monterey climate
station and an 83 in Santa Cruz. The high of 83 in Santa Cruz came
within one degree of matching the all-time January record of 84
set just last year (january 16 2014).
Fog and low clouds are largely absent from the Central Valley this
evening...unlike the past two evenings when fog blanketed the
Central Valley...and then subsequently developed into our north
and East Bay valleys overnight. However...the low levels remain
relatively moist and would expect areas of fog to redevelop in
the north and East Bay valleys late tonight and persist into Monday
Evening water vapor satellite imagery shows the unseasonably
strong upper ridge over northern California beginning to move to the
east...a process that will continue into Monday. Meanwhile a weak
upper low west of Baja California will begin to lift to the north. High
clouds associated with this low center are drifting well out ahead
of it...already beginning to overspread the southern part of our
forecast area. The combination of increasing high clouds and
the weakening upper ridge will result in slight cooling on
Monday...especially across the southern part of our area where
highs will be from 5 to 10 degrees cooler compared to today.
The models have come into reasonably good agreement regarding the
track of the upper low and its associated precipitation. The general idea
is for the low to drift due north Monday and Monday
night...approaching Point Conception by late Monday night...with
the low then transitioning to an open wave and shearing apart as
it traverses south-central California on Tuesday morning. The NAM
continues to be the most bullish of the models in regard to precipitation
potential from this system...forecasting light rain to overspread
all of Monterey and San Benito counties on Monday night...with
rain then reaching as far north as Palo Alto and Livermore by
daybreak Tuesday. The 00z GFS is wetter compared to its
previous runs and is now similar to the NAM in terms of how
much of our forecast area will get wet. However...the NAM
continues to forecast greater rainfall amounts. The NAM forecasts
in excess of a half inch of rain across much of Monterey County on
Monday night and Tuesday morning...while the GFS forecasts only
about half that. Precipitable water values moving north out of
Baja California are lackluster up to this point...so it seems the NAM may be
overly optimistic. In any case...it's beginning to look likely
that at least our southern-most counties will get some measurable
rain out of this system...and probability of precipitation across Monterey and San Benito
counties may need to be raised depending on what the 00z European model (ecmwf)
By the time the system currently approaching from the south exits
to our east late Tuesday...another weak and complex system will be
approaching California from the west and southwest...due to
arrive over California either Wednesday or Wednesday night. The models
agree that this midweek system will be too weak and disorganized
to produce precipitation over our area and will likely only generate some
An upper ridge offshore is expected to nose inland across northern
California during the second half of the week and maintain a dry weather
pattern through the end of January.
Aviation...as of 5:00 PM PST Sunday...offshore flow weakening but
airmass remains dry enough for VFR conditions. Central Valley fog
may still impact the interior north and East Bay valleys late
tonight. High clouds will move in from the south by Monday morning.
Vicinity of ksfo...VFR. Light offshore winds.
Ksfo bridge approach...similar to ksfo except areas of 5-6 mile
visibility in haze.
Monterey Bay area terminals...VFR.
Climate...record high temperatures are possible over the area today.
Here is the list of records along with the January warmest high
temperature readings and the latest year they occurred.
Sf Bay area...
Location today (1/25) January warmest
Kentfield 77/1934 79/1962
San Rafael 70/2014 82/1962
Napa 83/1899 85/1962
San Francisco 74/1899 79/1962
sfo Airport 68/2011 73/2014
Oakland 73/2014 78/2014
Oak Airport 70/2014 77/2014
Richmond 69/2011 76/1962
Livermore 73/1911 77/1911
Mountain View 72/2014 76/1948
San Jose 71/2014 79/1962
Gilroy 77/2014 80/2014
North central coast...
Monterey 78/1942 84/2014
Santa Cruz 80/1899 84/2014
Salinas 78/2014 87/2014
sns Airport 78/2014 86/2014
King City 77/2014 86/1976
Marine...as of 2:19 PM PST Sunday...light offshore flow near the
coast with southerly flow further offshore due to high pressure
over the Great Basin over the next 24 hours. Winds veer to the
south Tuesday with northerly winds returning late Wednesday.
Northwest swell will gradually diminish through the upcoming week.
Public forecast: dykema
aviation: west pi
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