Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1038 am PDT Thursday Jul 31 2014
Synopsis...the typical Summer weather pattern has returned to the
central coast with night/morning coastal low clouds and fog
stretching into the valleys with clearing skies in the afternoon
hours. Near normal temperatures and dry weather expected through
the forecast period.
Discussion...as of 9:15 am PDT Thursday...the current visible
satellite image is showing stratus along the coast and well into
the inland valleys this morning. When I left the house this
morning there was plenty of drizzle on my car and driveway...the
typical Summer weather pattern has returned. Also evident on the
visible satellite image are some high clouds moving in from the
west. These clouds are associated with a 50 knots jet maximum which will
pass over the forecast area today. The jet maximum and clouds are not
significant but will make our skies a little more interesting to
look at once the low clouds burn off.
The 0000z European model (ecmwf) and 1200z gfs40 have initialized well with the
current synoptic pattern and remain in good agreement through the
forecast period. Both models maintain a ridge of high pressure
over the western Continental U.S. Through the weekend with a weak upper level trough
developing along the coast by the beginning of next week. At the
surface a thermal through positioned along the coast will promote
warm seasonal temperatures inland and cool temperatures along the
Previous discussion...as of 3:03 am PDT Thursday...high clouds from
the former tropical system Hernan have exited the area and are now
over Nevada. Now satellite shows coastal stratus has spread into
inland areas. The marine layer depth is roughly the same as 24
hours ago...just over 1000 feet deep and the onshore surface
pressure gradient has increased with 3.0 mb between sfo and SAC.
Current temperatures and dew points are mostly similar to those
from yesterday at this time...although some stations are reporting
readings that are a few degrees cooler.
A broad upper level trough over the eastern Pacific will provide a
dry southwest flow aloft across the district through the remainder
of the week and into the weekend. Onshore flow is expected to
increase by late in the weekend which will allow for cooler air to
filter farther inland with near normal temperatures expected.
There could be a slight warm-up once again late next week as high
pressure aloft builds westward into California from the Desert
Aviation...as of 10:30 am PDT Thursday...marine layer has
deepened slightly to around 1500 feet this morning with stratus
extending well inland. Clearing is taking place quickly at this
hour. Ceilings are expected to return to mry Bay however models are
mixed on marine layer this evening around sf Bay.
Vicinity of ksfo...VFR today. West winds to near 20 knots this
afternoon. Ceilings late if at all.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...ceilings clearing within the next hour
or so. Ceilings return tonight.
Marine...as of 04:24 am PDT Thursday...northerly flow will
increase over the coastal waters today as high pressure builds off
the West Coast. Winds will be strongest north of Point Reyes.
Gusty winds will also be possible in the San Francisco Bay this
afternoon and evening. The increased winds will produce steeper
wind waves and locally hazardous conditions. Northwest swell will
increase Friday and over the weekend.
... Arena to pt Reyes 0-10 nm from 3 PM
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm from 3 PM
Small Craft Advisory...sf Bay north of the Bay Bridge from 1 PM
Public forecast: Larry
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