Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1004 am PST Sat Dec 27 2014
..colder weather expected Tuesday and Wednesday with the
potential for a strong offshore wind event...
Synopsis...slightly warmer temperatures are expected tonight as
high clouds and increasing dew points move into the area. A cold
storm system is expected to push into the forecast area Tuesday
bringing another round of cold temperatures and windy conditions
to the area.
Discussion...as of 9:57 am PST Saturday...it has been a cold
start to the day at many locations around the area. Numerous
reports of cold temperatures and photos of frost have been
gathered through social media. Some of the coldest temperatures
have been observed in southern Monterey and San Benito counties
with Pinnacles National Monument reporting 25...Fort Hunter ligget
26 and 29 in Hollister. Equally as cold temperatures where
observed in Santa Cruz County with Ben Lomond reporting
26...Felton 28 and Scotts Valley 29 degrees.
The cold airmass is well entrenched over the forecast area with
light offshore winds expected throughout the day today. The
current infrared satellite image is showing high clouds pushing towards
the area. NAM bufr time height analysis shows these high clouds
moving in over the forecast area overnight. In addition the NAM
bufr data and local WRF are showing surface relative humidity
increasing. The combination of the high clouds and increasing
surface relative humidity should slow the night time radiative
cooling...resulting in slightly warmer temperatures tonight for
most locations around the area. Therefore will not be issuing a
new freeze warning tonight.
The 1200z nam12 and gfs40 have initialized well with the current
synoptic pattern and remain in good agreement through the next 84
hours. Both of these models continue to show a cold trough of low
pressure sliding into northern California Monday night into
Tuesday. The models are coming into better agreement with the
timing and trajectory of this system which coincides with the
track and timing of the last European model (ecmwf) model run that we received on
1200z December the 26th. The dry Continental character of this
system is only expected to have total precipitable water values
between .1 and .2 inches. So not much if any precipitation is
expected with it. 1000 to 500 mb thickness drops to about 538 dm
so any precipitation that does fall will most likely be snow
showers over the hills.
Strong offshore winds across the North Bay mountains and East
Hills will be the greatest impact with this next storm system.
According the 1200z gfs40 925mb winds over the North Bay mountains
and East Bay hills are anticipated to reach 40 to 45 knots on
Tuesday. These gusty winds could cause down trees and power lines.
The second impact will be another round of cold temperatures for
the entire forecast area. We will continue to monitor this
approaching storm system.
Aviation...as of 10 am PST Saturday...VFR with light terrain
driven winds and excellent visibility today. High clouds will
stream in from the north through the day at or above 20000ft.
Vicinity of ksfo...VFR.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
Marine...as of 09:59 am PST Saturday...high pressure dominates
just offshore today which will lead to primarily light offshore
winds over the coastal waters. By Sunday evening... north winds
pick up on the heels of an inland storm system. Moderate north
winds will persist through the first half of the week. Northwest
swell will prevail through the weekend then gradually diminish.
Public forecast: Larry
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