Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1045 PM PST Wednesday Dec 11 2013
Discussion...as of 9:00 PM PST Wednesday...upper level ridge
extending from the eastern Pacific into northern California
combined with upper level low off the northern Baja California coast brought
an offshore flow to the area today. High temperatures today were
3-6 degrees warmer than yesterday. Offshore winds will keep
temperatures above freezing in the mountains so the freeze warning
was cancelled for the North Bay mountains. Low temperatures in the
valleys are expected to be a few degrees warmer tonight but will
still be cold enough for a freeze warning in the North Bay
A weak frontal system associated with an upper level trough will
move into the Pacific northwest on Thursday. Winds will switch to
onshore and milder air will move into the area. This will bring
an end to the freeze warnings at night as freezing temperatures
will be limited to the coldest wind-sheltered inland locations.
No precipitation is expected but a sprinkle may be possible in the North
Bay Thursday night.
From previous discussion...high pressure will continue to build
over the region from the weekend into the middle of next week.
Both the GFS and European model (ecmwf) indicate the building ridge. The European model (ecmwf) is
the stronger of the two models and actually develops 850 mb temperatures
over the region of 17c. If the European model (ecmwf) verifies that would be nearly
2 Standard deviations above normal and in the 99th percentile of
the warmest 850 mb temperatures during the month of December at koak
sounding site. Needless to say...temperatures next week could be
rather warm. Have bumped up maximum temperatures to above normal values next
Mon-Wed...but if models keep going this way temperatures will really need
increase high temperatures. Highs next Monday- Wednesday will generally be in the
60s to lower 70s...more 70s if the European model (ecmwf) is right.
Even though it is outside of our area one other weather item of
note is the extended forecast across the central Continental U.S.. it may be
fantasy land at this point...but the GFS and European model (ecmwf) develop a very
strong low (less than 1000mb) over Texas pan handle with a
1040-1050mb high over North Plains. That would be a rather impressive
pressure gradient along The Rockies. Additionally...the European model (ecmwf)
brings 850 mb temperatures of -35c into the northern plains around
Aviation...as of 10:42 PM PST Wednesday...clear skies. Light
winds. The pressure gradients continue to favor an offshore wind
direction this evening. Inbound trough over the eastern Pacific
will bring some high cloudiness to the area later Thursday. Local
pressure gradients will likely turn weak onshore by Thursday
Vicinity of ksfo...VFR. Light winds.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
... Warning...North Bay valleys
Public forecast: west pi
Visit US at www.Weather.Gov/sanfrancisco
Follow US on facebook, twitter, and youtube at: