Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
227 PM PST Tuesday Dec 10 2013
Discussion...as of 2:27 PM PST Tuesday...weather highlights
through the period include one more night of cold weather
followed by a warm up.
Given the cold start to the day it is not surprising that many
locations are struggling to warm up despite ample sunshine.
At least temperatures are running a few degrees warmer than
yesterday at this time. Maximum temperatures this afternoon will top out in
Synoptically speaking...an upper level low remains off the socal
coast...a cold dome continues to impact much of a the Midwest and
northeast while high pressure builds off the Pacific northwest coast.
the major weather concern during the short term continues to be
the lingering cold weather for tonight. Not an easy forecast
tonight as the airmass is forecast to warm aloft with building
high pressure and NE flow...especially over the higher elevations.
The most notable warming per model guidance will be over the
higher terrain. Coldest temperatures will be across the interior
valleys and higher terrain where wind will not be much of a
factor. Decided to not include the Santa Cruz mts and East Bay hills
(freeze warning) since NE flow will keep temperatures above
freezing for the most part and in some spots near 40. It should be
noted though any protected area in the Santa Cruz mts or East Bay
hills that does not experience NE winds will be near freezing.
Currently do not feel these locations are widespread enough to
warrant a freezing warning. Therefore...a freeze warning remains
in effect North Bay mts/valleys...East Bay valleys and interior
Monterey/San Benito counties. Temperatures near the coast and San
Francisco Bay shoreline will be warmer than last night...but still
widespread low to middle 30s to warrant a frost advisory. A frost
advisory was issued for coastal North Bay...sf Bay shoreline...sf
peninsula coast...north Santa Clara Valley...Monterey Bay coast and
Big Sur coast. One final note...Santa Clara Valley is split with
San Jose in a frost advisory and Morgan Hill/Gilroy in a freeze
After tonight...high pressure builds over the region with warming
850mb temperatures and rising 500 mb all leading to a warming trend. In
fact...temperatures later this week could at or above seasonable
levels. Previous model runs tried to bring some moisture to the
central coast on Friday...but latest runs keep all moisture off
the coast. Only mention of precipitation will be for the northern coastal
quiet high pressure will likely dominate the West Coast through
the middle of the month. The European model (ecmwf) builds a 590 Dam Ridge with the
GFS showing a ridge over 582 dam. Anyway you slice it...it looks
dry and mild.
Interesting note from previous discussion...
for your information...looking all of the way out through Christmas day currently
shows dry conditions remaining across our entire area. 384 hour
accumulated precipitation off the 0z operational GFS shows almost
all of California without any precipitation for the next 16 days. In
addition, the GFS ensemble shows at best a 20 percent chance of
picking up a little light rain during just a short period around
the 24th of December with all other time periods dry. The Canadian
ensembles also indicate dry weather through Christmas day. If the
models verify it would mean that downtown San Francisco will need
to pick up well over 3 inches of rain in just the final seven
days of 2013 to not have the driest calendar year on record (keep
in mind records there date back all of the way to 1849).
Aviation...as of 9:20 am PST Tuesday...surface high pressure will
keep the region clear with mainly light and variable winds. Light
onshore flow may briefly develop this afternoon.
Vicinity of ksfo...VFR conditions and light winds will prevail
through the forecast.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR conditions will prevail through
the forecast. Moderate offshore winds will be present at ksns into
the late morning hours and again Wednesday morning.
... Advisory...North Bay coast...sf Bay
shoreline...sf peninsula coast...
north Santa Clara Valley...Monterey
Bay coast and Big Sur coast.
Freeze warning...North Bay mts/valleys...East Bay valleys
Salinas valley...interior Monterey
County and San Benito County.
Public forecast: mm
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