Scientific Forecaster Discussion
fxus66 kmtr 301032
Area forecast discussion
National Weather Service San Francisco Bay area
332 am PDT Tue may 30 2017
Synopsis...continued seasonably cool and breezy weather will
continue along with a chance of showers tonight into Wednesday as
an upper trough moves through. A drying and warming trend
Thursday into next weekend.
Discussion...as of 3:30 am PDT Tuesday...similar to yesterday, a
combination of a moderate marine layer (now around 2000 feet)
combined with continued onshore flow at the surface (over 3 mb)
from sfo to sac) is leading to clouds for many locations.
However, interesting to note that parts of the North Bay are
actually staying cloud-free. Latest ob from Santa Rosa indicates
clear skies. Clouds are forecast to clear toward the coast late
this morning or early in the afternoon. Highs will be in the 50s
and 60s near the water with 70s to lower 80s inland. Breezy
westerly winds can also be expected.
Synoptically a trough will advance to the West Coast later today
with the axis forecast to swing through our County Warning Area late tonight.
Moisture associated with this feature along with more
instability/positive vorticity advection will likely trigger a few showers across our
region. Models have trended a bit wetter compared to 24 hours ago,
so pops were increased. Focus still remains on eastern and
southern sections especially around San Benito County. If that
verifies it would be opposite of how precipitation is typically
distributed. Rainfall amounts should be light -- less than a
tenth, and many urban spots will likely see little to no rainfall.
The axis will move to the east while 500 mb heights begin to
slowly rebuild going into the end of the week. This will lead to a
return of dry weather along with warmer temperatures. The ridge
is expected to further strengthen through next week with
afternoon highs likely going to above normal levels. Also Worth
noting enough mixing should occur that the marine layer has a
better chance of scattering out. Coastal spots might actually have
a shot of a few days of sunny weather.
Aviation...10:49 PM PDT Monday for 06z tafs...low clouds are
slowly filling in across the region under a 2000 foot marine
layer. MVFR to IFR cigs anticipated overnight. A repeat of today
conditions/cigs are expected Tuesday with some locations only
seeing partial clearing, if any. Moderate to locally strong and
gusty winds will ease a bit overnight.
Vicinity of ksfo...IFR cigs will prevail through tonight. Cigs
are anticipated to lift to MVFR after 19z Tuesday however only
partial or temporary clearing is expected if any. Moderate to
locally strong and gusty westerly winds will persist through late
tonight then diminish slightly overnight to around 10 to 15 kt
Sfo bridge approach...low clouds will fill in across the Bay
overnight. Clouds over the approach are anticipated to scatter out
around 21z Tuesday afternoon.
Monterey Bay terminals...IFR cigs expected through tonight. Cigs
may lower to LIFR around 400 ft overnight. Cigs over kmry are
anticipated to lift to MVFR after 18z Tuesday however only partial
or temporary clearing is expected if any. Cigs over ksns will
scatter out around 19z. Moderate westerly winds will persist
through this evening then gradually diminish overnight.
Marine...as of 03:20 am PDT Tuesday...high pressure off the West
Coast and low pressure inland will maintain gusty northerly winds
through at least Tuesday night. The gusty winds will generate
steep wind waves and fresh swell...making for adverse and
hazardous seas. Winds are forecast to decrease Wednesday as a weak
front moves through the area and the surface pressure gradient
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...mry Bay
Small Craft Advisory...sf Bay from 12 PM
Public forecast: Bell
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