Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
919 am PST Wednesday Dec 11 2013
Discussion...as of 9:19 am PST Wednesday...interesting night
across the County Warning Area as the cold air tries to hang on. The coldest
readings overnight once again occurred away from the coast and
higher ridges. Temperatures in the inland valleys...fell below
freezing with a few spots in the upper teens. The cold air was
much more shallow this morning as noted on the koak sounding. The
koak sounding also indicated that 850 mb temperatures were as much as
3-4c warmer today compare to yesterday...but at the surface temperatures were
similar. Additionally...taking a quick look at observations on
Bay area ridges showed much warmer conditions. In some locations
temperatures overnight were as much as 15 degrees warming. For instance
the Santa Cruz Mountains and Santa Lucia mountains stayed in the
40s for much of the night.
Given the warmer start to the day and a warmer airmass in place
today/S maximum temperatures will be warmer than yesterday. Many locations
south of San Jose will break 60 degrees where other locations
will be in the 50s to near 60.
Not update planned at this time.
For tonight...the cold airmass will continue to linger...but
mostly for the North Bay. A freeze warning will remain in effect for
the North Bay valleys and mountains as temperatures will drop down into
the 25 to 30 degree. Elsewhere...the airmass should remain mixed
enough to not warrant a frost or freeze.
Previous discussion...a storm system will drop down late
Thursday into Friday. Computer guidance continues to keep any
moisture out of our County Warning Area expect for far northwest waters. Only impact
could be a slight increase in clouds for northern parts of the
County Warning Area.
Temperatures will continue to warm over the weekend into next
week as an unusually strong ridge of high pressure for this time
of year(approaching 590 dm) builds in from the eastern Pacific.
850 mb temperatures will also warm at the same time and conditions at the
surface will jump to well above normal values. Looking at the
basic MOS guidance shows parts of Monterey County even getting
into the lower 70s (even 71 in Monterey!) With middle to upper 60s
for a large portion of the rest of the County Warning Area. Feel that we have a
good shot of setting a few record highs for the first half of next
Longer range forecast is slightly different from yesterday as a
longwave trough is now expected to drop down into our area Thursday
or Friday. Most guidance keeps dry conditions for our area,
although the operational European model (ecmwf) does bring some moisture to our
County Warning Area. Even if that verifies, at this time it does not look
substantial. Will definitely hold off getting excited about that
due to the poor track record of the extended European model (ecmwf) over the past
couple of months. Worth noting that the models do build another
very large block out over the Pacific by the end of next week which
would prevent any atmospheric rivers from setting up. Our much
drier than normal winter looks like it will continue at least to
Aviation...as of 3:15 am PST Wednesday...VFR conditions with
mainly light offshore flow will continue across the region for at
least the next 24 hours. High confidence.
Vicinity of ksfo...VFR conditions with light winds will prevail
through the forecast. High confidence.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR conditions will prevail through
the forecast. Moderate offshore winds at ksns will become light
and variable late this morning into the afternoon hours.
Public forecast: mm
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