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Area forecast discussion 
National Weather Service San Francisco Bay area
517 am PDT sun Jul 5 2015

Synopsis...a persistent marine layer and light onshore flow will
result in widespread night and morning low clouds...patchy fog
and possible drizzle in coastal locations through much of the week.
Otherwise...dry weather conditions will persist with temperatures
gradually cooling through midweek.

&&

Discussion...as of 3:30 am PDT Sunday...an upper low offshore is
currently centered about 500 miles west-southwest of San Francisco...and is
moving very slowly to the east-northeast. The models agree that this low will
gradually approach the California coast over the next several days
in a meandering and halting eastward trajectory. The approach of
this upper low should result in continued deepening of the marine
layer (currently 2000 feet deep at fort ord). This will mean
widespread night and morning low clouds and patchy fog through
much of the week...along with local late night and early morning
drizzle in coastal locations.

High temperatures on Saturday were close to normal...and a little
warmer than normal in the inland valleys most isolated from marine
influence. Daytime temperatures are expected to gradually cool through
midweek as the upper low approaches. By midweek inland
temperatures are forecast to be anywhere from 5 to 10 degrees
below normal...and as much as 25 degrees cooler compared to a week
earlier.

Satellite and model data indicate there is at least some moisture
associated with the upper low offshore. And...the models indicate
that as the low draws closer to the coast later this week...it may
tap into some of the monsoonal moisture to our east. Thus...there
appears to be a small chance of convective precipitation somewhere in
our area later this week. In fact...the 00z GFS forecasts
scattered precipitation across the southern half of our County Warning Area between
Wednesday evening and Thursday evening...while the 00z European model (ecmwf) shows
light quantitative precipitation forecast across the eastern fringes of the sf Bay area late
Thursday night into Friday. There has not yet been enough model
consistency regarding the potential for convective precipitation with
this system to explicitly add shower/thunderstorm chances to the
forecast. In addition...location of precipitation chances is hard to pin
down given that the GFS and European model (ecmwf) show differing trajectories for
the low as it comes ashore. Will not yet add precipitation chances to
the forecast for later this week...and rather wait until there is
better model consistency and agreement.

The low is expected to finally move inland and off to our east by
next weekend...ending all potential for precipitation by Saturday and
allowing temperatures to begin warming.

&&

Aviation...as of 5:10 am PDT Sunday...stratus does not appear as
widespread as yesterday as there are some holes around the sfo Bay
area. Marine layer has remained steady around 2000 feet with similar
gradients as yesterday. Ceiling heights have remained above 1000 feet
in the sfo Bay area. Stratus cleared rather early yesterday and
with similar conditions today clearing for today is expected to be early
again.

Vicinity of ksfo...MVFR ceilings through 17z.

Ksfo bridge approach...similar to ksfo.

Monterey Bay area terminals...some breaks over mry Bay suggests
there may be clearing this afternoon. IFR ceilings clearing after
17-18z.

&&

Marine...as of 5:15 am PDT Sunday...a 1028 mb high is located
900 nm northwest of Cape Mendocino. Weak low pressure is off the
California coast. This will result in light winds and seas through
Thursday.

&&

Mtr watches/warnings/advisories...
... Bay from 3 PM

&&

$$

Public forecast: dykema
aviation: west pi
marine: west pi



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