Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
313 am PDT sun Aug 2 2015
Synopsis...a subtle cooling trend is forecast to continue through
Tuesday as onshore flow and the marine influence increases. Modest
warming is then forecast for Wednesday and Thursday. Aside from
patchy coastal drizzle and fog during the overnight and early
morning hours...dry weather conditions are expected to persist
through the forecast period.
Discussion...as of 3:10 am PDT Sunday...an upper level ridge
continues to dominate the western Continental U.S. While a weak trough is
nearly stationary off the West Coast between 130 and 140w. Over
the next few days the ridge is forecast to weaken and shift east.
At the same time...weak impulses ejecting out of the trough
offshore will track to the east-northeast and across northern and central
California. These developments will result in modest cooling over
the next three days...with daytime temperatures across inland areas
forecast to drop to as much as ten degrees below normal by
Tuesday. Widespread night and morning low clouds will clear inland
by midday each day...but only partial afternoon clearing is
expected at the coast.
By midweek the trough offshore is forecast to deepen and form a
cutoff low out near 140w. Downstream from this deepening trough a
shortwave ridge will develop over central and Southern California.
This will result in a brief warm-up on Wednesday and
Thursday...primarily across inland areas.
The upper low that will develop offshore by midweek is forecast
to lift to the northeast late in the week and across California by
Saturday. Cooling is expected beginning on Friday as the low
approaches. Most model guidance has suggested this low will not
have sufficient moisture and/or instability to produce convective
precipitation in our area late in the week. However...the 00z GFS
develops precipitation just offshore by Thursday evening...and then just
to our east by Friday afternoon. There is not yet enough model
support to justify adding shower/thunderstorm chances to the
forecast...but it's something to keep an eye on for late in the
extended forecast period.
Aviation...as of 10:57 PM PDT Saturday...the stratus has filled
back in quicker than previously forecast. Koak...ksfo...kmry and
ksns are all reporting MVFR ceilings. Marine based inversions are
holding steadily at about 2000-2200 feet...and more stratus as
well as fog are expected to develop overnight.
Vicinity of ksfo...MVFR ceiling tonight. Clearing forecast by 17z.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...MVFR with gradual transition to IFR
ceilings forecast tonight. Middle to late morning clearing expected
Marine...as of 2:49 am PDT Sunday...weak low pressure off the
Southern California coast will keep light winds through Tuesday.
High pressure will start to build off the northern California
coast bringing increasing northwest winds. Seas will be mixed
northwest swell and long period south to southwest swell into next
Public forecast: dykema
marine: west pi
Visit US at www.Weather.Gov/sanfrancisco
Follow US on facebook and twitter at: