Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
333 PM PST Sat Dec 27 2014
..colder weather expected Tuesday and Wednesday with the
potential for a strong offshore wind event Tuesday night...
Synopsis...approaching high clouds and increased surface humidity
will provide slightly warmer temperatures tonight across the
forecast area. However...some sheltered low lying spots may
experience freezing temperatures overnight. 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 2:40 PM PST Saturday...after a cold start to
the day afternoon temperatures remain in the 50s. Although...a
cold airmass is in place increasing surface humidity and high
clouds will slow radiative cooling enough to provide a slightly
warmer night across the forecast area.
The 1200z European model (ecmwf) along with the 1800z nam12 and gfs40 have
initialized well with the current synoptic pattern and remain in
good agreement through the next 84 hours. All three models have
come together on the timing and location of an approaching cold
storm system which is anticipated to make its way into the Great
Basin on Sunday. Timing on the arrival of the storm to northern
California remains to be in the Monday night Tuesday morning time
frame. As previously mentioned this storm system appears fairly
dry with forecast total precipitable water values between .1 and
2 inches. This dry cold airmass will cool the atmosphere rapidly
once it arrives to the San Francisco...Monterey Bay area on
Tuesday. In fact 1000 to 500 mb thickness drops to about 524 dm so
any precipitation that does fall will most likely be snow showers
over the hills.
The greatest impact associated with this storm system will be strong
offshore winds across the North Bay mountains and East Hills. According
the 1800z gfs40 925mb winds over the North Bay mountains and East
Bay hills are anticipated to reach 45 to 50 knots on Tuesday evening. These
gusty winds could cause down trees and power lines.
Aviation...as of 3:30 PM PST Saturday...high pressure over the
Great Basin will keep dry offshore flow through Sunday.
Vicinity of ksfo...VFR.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
Marine...as of 3:30 PM PST Saturday...high pressure will continue
to dominate the eastern Pacific and result in light offshore
winds through early tomorrow. Moderate north winds are expected to
return late in the weekend and into early next week. Steep fresh
north swell will move into the coastal waters late Monday into
Public forecast: Larry
aviation: west pi
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