Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
434 am PDT Sat Aug 1 2015
Synopsis...a cooling trend is expected to continue into the
weekend as onshore flow increases and the marine layer deepens. No
sign of organized rainfall through next week.
Discussion...as of 3:00 am PDT Saturday...not much to talk about
for the forecast package today as subtropical moisture continued
to moved out of our County Warning Area overnight while the marine layer has
deepened close to 2000 feet and the surface gradient has switch
from west-northwest to west-southwest. At the same time 850 mb temperatures are forecast to be
around 4c compared to yesterday. All of this will lead to
additional cooling along with widespread clouds this morning both
at the coast and adjacent valleys. Highs will be mostly in the 60s
to middle 70s at the coast with upper 70s to near 90 for most inland
spots. In some cases inland locations will be 10 degrees cooler
Synoptically the flow aloft will switch to the SW as an area of
low pressure forms to our west and slowly advances to our coast.
Subtropical moisture is not expected to become entrained in the
flow of the low so only impact will be to drop temperatures a few
additional degrees. Coastal fog will be possible most mornings.
This pattern may hold all of the way through next weekend.
Aviation...as of 4:30 am PDT Saturday...southerly flow above the
marine layer has acted to clear out the clouds from sfo and Oak
this morning. The question is whether clouds will return.
Satellite image shows areas of ceilings over the southern sfo Bay
area. These clouds are expected to spread north and bring ceilings
into sfo and the approach by 14z. With the marine layer at around
2000 feet ceilings should stick around through 19z.
Vicinity of ksfo...MVFR ceilings returning by 14z. Clearing after 18z
at the Airport...19z over the approach. West winds 20 knots after
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...widespread ceilings cover mry sand sns
this morning. Southerly flow will bring local adiabatic warming
which will clear out the clouds after 18z.
Marine...as of 02:56 am PDT Saturday...a weak onshore surface
pressure gradient will maintain generally light winds and gentle
seas through the weekend. Although...generally light winds are
expected to prevail please keep in mind that the afternoon sea
breeze can be gusty this time of the year.
Public forecast: Bell
aviation: west pi
marine: west pi
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