Scientific Forecaster Discussion
fxus66 kmtr 221727
Area forecast discussion
National Weather Service San Francisco Bay area
1027 am PDT Mon may 22 2017
Synopsis...high pressure will maintain very warm and dry
conditions for inland areas through today. A shallow marine layer
and weak seabreeze will keep the coast seasonably cool. A cooling
trend is expected regionwide from Tuesday through Friday. Warming
is then expected for inland areas during the upcoming weekend.
Discussion...as of 8:00 am PDT Monday...a boost in the depth of
the marine layer combined with a more pronounced onshore flow lead
to widespread clouds and patchy fog along the coast plus into the
Salinas valley. Clouds are expected to burn back to the coast
later this morning. However, big question remains if sunshine will
make it to the coast or not. Will monitor conditions and provide
an update to the forecast if necessary.
Otherwise, main story for the week will be cooler conditions over
the next several days as the ridge of high pressure flattens out
as a low dives down from the northwest. Temperatures will start to
rebound by the weekend as a weak ridge rebuilds into our region.
Previous discussion...an upper level ridge remains centered
along the West Coast early this morning...maintaining a warm
airmass across inland areas. However, the marine layer is deeper
this morning (about 1200 feet deep at fort ord) and onshore
pressure gradients are slightly greater. The result will be more
widespread morning low clouds and fog near the ocean and locally
into the coastal valleys, and cooler daytime temperatures in these
areas as well. Inland areas that remain isolated from the effects
of the marine layer will continue to be very warm today.
The upper level ridge is forecast to weaken on Tuesday and then
completely break down by Wednesday as an upper trough currently in
the Gulf of Alaska drops southeast and into the western United
States. These developments will result in robust cooling across
our entire region, especially inland, from Tuesday through
Thursday. Daytime highs will cool by as much as 20 degrees by
midweek. In addition, night and morning low clouds will be much
more widespread and persistent by midweek.
The upper trough will shift east by the weekend, allowing an upper
ridge to redevelop near the West Coast. Modest warming is expected
inland over the weekend. However, moderate onshore flow will limit
weekend warming potential near the coast.
Aviation...as of 10:26 am PDT Monday...for 18z tafs. Shallow
marine layer is eroding back to the coast as 18z tafs become
valid. VFR at all terminals this afternoon with breezy sea breeze
conditions this afternoon. Shallow marine layer will return
tonight with fog possible.
Vicinity of ksfo...VFR through early tonight. Based on latest
model guidance and what happened this morning will bring low
clouds back into sf Bay. The low confidence area will once again
be sfo itself. Went with a pessimistic forecast tonight with a few
hours of clouds/fog tomorrow before a quick burn off.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR this afternoon. Cigs return this
evening with IFR to LIFR conditions possible.
Marine...as of 10:23 am PDT Monday...high pressure building over
the Pacific northwest will maintain light to moderate
northwesterly winds through midweek. Winds will increase midweek
as a thermal trough develops along the coast tightening the
pressure gradients over the northern outer waters. Strongest winds
are expected over the outer waters while the inner waters remain
... Bay from 12 PM
Public forecast: Bell/dykema
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