Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
853 PM PDT Sat Sep 20 2014
Synopsis...isolated showers will linger across portions of the
north and East Bay through the remainder of Saturday evening.
Otherwise little change is expected in our weather through early
next week. A Pacific storm system will bring a possibility of rain to
the area by midweek...as well as the first large northwest swell
of the season.
Discussion...as of 8:50 PM PDT Saturday...an upper low is lifting
northeast across central California this evening. This low
triggered widespread convection over the central and southern
Sierra this afternoon. In addition...scattered showers
and isolated thunderstorms developed over the northern San Joaquin
Valley by early evening which prompted a forecast update to add a
slight chance of showers and thunderstorms to eastern Contra Costa
and Alameda counties...as well as Napa County. A few showers have
been tracking across northeast Contra Costa County since about 7
PM this evening and current radar shows a light shower approaching
the city of Napa. All thunderstorm activity has remained to the
east of our area...although one strike was detected about midway
between Brentwood and Stockton around 7:20 PM this evening.
Satellite and radar indicate shower/thunderstorm activity has been
on the decrease since sunset. Would expect a decreasing trend to
continue through the rest of the evening with all activity likely
to end by midnight.
Sunday is expected to be a day much like today with low clouds
clearing in most areas by midday. High temperatures will remain
slightly below normal inland and near normal in coastal areas. The
upper low will have moved well off to our east by Sunday morning
and dry weather will prevail. Dry weather will then continue
through at least Tuesday as a shortwave ridge develops over the
west...downstream from a deepening trough over the eastern
Pacific. A cold front associated with that trough is forecast to
spread rain across much of the northern part of our region from late
Wednesday through Thursday morning. Showers chances will then continue
through the remainder of Thursday and into Friday as the upper
trough slowly moves inland. Isolated showers could even linger
into next Saturday if the European model (ecmwf) were to verify.
Aviation...as of 4:45 PM PDT Saturday...stratus is extensive
along the coast. Marine layer has deepened to near 2000 feet.
East-west onshore gradient is weak but starting to increase. Thus there
is a better chance of an early return into sfo.
Vicinity of ksfo...MVFR ceilings after 03z.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...stratus already extends several
miles inland. MVFR ceilings will lower to IFR after 04-06z.
Marine...as of 10:55 am PDT Saturday...light south to
southwesterly winds are expected across the northern coastal
waters through the weekend. Elsewhere...west to northwesterly
winds will prevail and persist through the first half of the week.
Light seas will continue through the first half of the week. A
longer period west to northwest swell is forecast to impact our
area starting on Wednesday.
Public forecast: dykema
aviation: west pi
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