Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
851 PM PDT Monday Aug 31 2015
Synopsis...aside from the possibility of coastal drizzle the
next few mornings...dry weather conditions will persist through
the workweek. Temperatures will cool slightly for the the latter
half of the week as an upper level trough drops southward into the
Discussion...as of 8:50 PM PDT Monday...a thermal trough and
mainly clear skies across the region today resulted in warmer
temperatures over most locations with exception of the coast where
slightly cooler temperatures were felt as a result of the typical
Latest satellite imagery reveals patchy low clouds beginning to
form along the coast at this hour. Models show increasing
boundary layer moisture however a robust 4.7 mb gradient from
acv-sfo will likely keep any stratus that forms patchy in nature.
Drizzle may accompany patchy stratus along the coast by morning as
a trough off the coast deepens and shift slightly toward the
coast in turn deepening the marine layer.
Sunny skies and slightly above normal temperatures are expected
once again Tuesday as very little change is anticipated in the
overall weather pattern. Patchy coastal stratus will clear to the
coast by noon.
From previous discussion...by Tuesday night into Wednesday
morning...another weak middle/upper level short-wave disturbance is
forecast to approach the region from our southwest and enhance the
possibility of coastal drizzle. Meanwhile...a stronger upper level
low is forecast to drop southward into the Pacific
northwest...cooling 850 mb temperatures over our region. This will
result in a cooling trend over the San Francisco/Monterey Bay
region for Wednesday into Thursday. The cooler and drier air mass
advecting southward over the region late week should cause the
marine layer to mix out...limiting coastal clouds and ending the
possibility of coastal drizzle.
Dry conditions will persist into the upcoming weekend as the
upper level trough axis remains stretched across northern
California northward into the Pacific northwest. Temperatures will
also continue on the cool side of normal through at least Saturday
afternoon. The trough will then lift to the northeast late in the
weekend into early next week...allowing temperature to rebound
back to near seasonal averages.
Aviation...as of 5:24 PM PDT Monday...the northerly gradient is
again a little under-forecast by the mesoscale model today.
There's a bit more surface ridging than the models are picking up
on from Humboldt County to Mendocino County which is steepening
the acv-sfo gradient to 4.6 mb. The uki-sts gradient is near flat.
The Bodega Bay profiler shows no marine layer due to a combination
of subsidence over the area and mostly light north-northwest wind.
Most of the Bay area is clear. High confidence VFR will hold over
the Bay area through much of the evening as an area of subsidence
lingers into the evening. Coastal stratus and fog with some inland
intrusion becomes more likely late tonight.
Vicinity of ksfo...VFR. Westerly winds 19-25 knots until 03z. Tempo
MVFR ceiling 10z-14z Tuesday morning. San Carlos sodar shows marine layer
inversion based near 1700 feet. Moderate to high confidence.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...visible imagery shows a small area
of stratus over the peninsula. Fort Ord profiler shows the marine
layer inversion based near 1600 feet. Forecast is VFR followed by
ceiling redevelopment between 03z-07z this evening. IFR ceilings tonight.
Moderate to high confidence.
Marine...as of 2:40 PM PDT Monday...a significant surface
pressure gradient will maintain moderate northwesterly winds
across the coastal waters through a majority of the work
week...the strongest of which are expected to occur over the
northern outer waters. These gusty winds will promote
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm until 11 PM
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Public forecast: CW
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