Scientific Forecaster Discussion
fxus66 kmtr 261741
Area forecast discussion
National Weather Service San Francisco Bay area
1041 am PDT Wed Jul 26 2017
Synopsis...a gradual warming trend will get underway today and
continue through Friday. By Thursday and into the weekend,
afternoon temperatures will warm to above seasonal averages for
inland areas while coastal locations remain cool. Above average
temperatures are then likely to persist into early next week.
Discussion...as of 08:14 am PDT Wednesday...visible satellite
imagery shows a widespread stratus intrusion this morning
associated with 2,000 ft marine layer. The stratus has managed to
push well into the Salinas valley, Sonoma Valley, and across much
of the San Francisco Bay area. With stratus impacting similar
areas as yesterday, temperatures across the region are running
within a few degrees from what they were 24 hours ago. Expect
clearing to occur for many by late morning, though some coastal
locations may see overcast skies into the afternoon. An upper-
level low currently sits just off the northern California coast
and we'll see continued onshore flow across the area this
afternoon. Most inland locations can expect a few degrees of
warming today, with additional warming heading toward the weekend
as high pressure begins to build over the region. No major
changes made to the forecast this morning. For additional details
please refer to the previous discussion sections.
Previous discussion...as of 3:47 am PDT Wednesday...satellite imagery
shows coastal stratus and fog has locally filled into inland
valleys. The Fort Ord profiler indicates a marine layer depth is
persisting around 2000 feet. A weakening upper level trough over
northern California will maintain onshore flow today with high
temperatures expected to be similar to or slightly warmer than
those from Tuesday, with 60s to lower 70s at the coast, and 80s
and 90s inland.
High pressure aloft will then build into California from the
Desert Southwest bringing warmer temperatures to the area,
especially inland. The marine layer will compress keeping stratus
near the coast. High temperatures in the warmest inland areas are
forecast to warm well into the 90s, with some of the warmest
areas exceeding the century mark by Thursday and Friday. Another
trough approaching from the west will lower heights somewhat over
the weekend, thus bringing slight cooling to the area.
Medium range models keep a strong ridge over the Rocky Mountain
states early next week. Little change in temperature trends is
expected going into next week with warmest inland locations seeing
highs in the 90s to near 100. Near-coastal areas will stay in the
60s. The European model (ecmwf) and GFS have differing solutions regarding where
moisture from hurricanes Irwin and Hilary end up. The GFS brings
moisture from Hilary up to the Southern California coast by next
Wednesday while the European model (ecmwf) takes both systems to the west.
Aviation...as of 10:40 am PDT Wednesday...for 18z tafs. Stratus
is beginning to retreat to the coast. Still seeing MVFR cigs at
ksfo and koak. Expecting VFR conditions to develop in about an
hour. VFR this afternoon with return of cigs expected tonight. Low
confidence on coverage of stratus based on compression of the
marine layer due to building high pressure. Gusty west to northwest winds
Vicinity of ksfo...currently MVFR cigs as stratus continues to
dissipate. VFR conditions probable around 1830z. VFR conditions
this afternoon with gusty west to northwest winds. Possible return of low
cigs tonight, but low confidence.
Sfo bridge approach...similar to ksfo. Approach may clear sooner
than ksfo this morning.
Monterey Bay terminals...MVFR cigs at kmry as stratus retreats out
to the Bay. Expecting VFR conditions within the hour. VFR to
prevail this afternoon before return of low cigs tonight.
Marine...as of 8:31 am PDT Wednesday...winds will gradually
increase and transition to west and northwesterly across the
waters today. Most significant increases in wind speed will be
north of Point Reyes. Tropical disturbances in the Pacific will
generate a long period southerly swell that will reach the coastal
waters by Friday.
... Bay from 1 PM
Public forecast: Rowe/Sims
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