Scientific Forecaster Discussion
fxus66 kmtr 240547
Area forecast discussion
National Weather Service San Francisco Bay area
1045 PM PDT Tue may 23 2017
Synopsis...an inland cooling trend will continue through late week
as high pressure weakens and the marine influence increases. Minor
warming is then expected during the upcoming weekend as high
pressure returns to the West Coast.
Discussion...as of 08:20 PM PDT Tuesday...only minor adjustments
made to sky cover based on current trends. As of 7:50 PM PDT,
visible satellite showed an extensive area of low clouds off the
coast and impacting parts of the Bay area with the clouds
intruding through the Golden Gate east to Berkeley. Fort Ord
profiler shows the marine layer around 1,500 ft this evening.
Tuesday was another warm day for inland locations with highs ranging
from the 80s to low 90s. Don't expect to see any 90s tomorrow as
the ridge responsible for bringing the well above normal
temperatures continues to push east into the continent. Most
inland locations can expect to see temperatures about 5 to 10
degrees cooler on Wednesday. Additional cooling will occur from
Wednesday to Thursday as an upper level low centered over
southwestern Canada allows for 500 mb heights to continue to fall
over the region. High temperatures by Thursday will fall to the
upper 60s to mid 70s across the East Bay and South Bay, as well as
the Salinas valley. Coastal locations can expect widespread
middle 50s to middle 60s with marine stratus.
Models suggest another ridge to build over the West Coast in time
for the Holiday weekend, though at this point it doesn't look that
it'll be as warm as it was over the past few days. Temperatures
should be at or within several degrees of climatological normals
for the end of may.
Previous discussion...as of 01:32 PM PDT Tuesday...low clouds continue to
hug the coast this afternoon with mostly sunny skies inland. With
this, the warmest temperatures persist over inland areas while
cooler temperatures (generally in the upper 50s to lower 60s) are
common at the coast. This trend will likely persist into tomorrow,
with low clouds spreading inland this evening and into the
overnight hours with a marine layer of around 1500 feet in place.
However, as the ridge aloft weakens and onshore flow increases,
inland locations will see the gradual cooling trend continue into
Wednesday. With the deepening marine layer, cannot rule out patchy
coastal drizzle/mist during the late night and early morning.
However, measurable precipitation is highly unlikely.
Further cooling is expected late in the week as the ridge flattens
and an upper level low drops down into the northern rockies. With
this and an increase marine influence, looks for temperatures to
fall below seasonal averages for just about all inland locations.
More widespread 60s and 70s will be likely during the afternoon hours
beginning on Thursday and continuing through Saturday.
By late in the weekend and into early next week, a ridge of high
pressure is currently forecast to rebuild over the West Coast. This
would likely result in a slight warming trend with afternoon
temperatures back to near seasonal averages. In addition, look for
mostly sunny afternoon conditions inland while coastal clouds will
Aviation...as of 10:44 PM PDT Tuesday...a deepening marine layer
will usher in increasing marine based stratus and fog this evening
into Wednesday morning. IFR cigs will likely transition to MVFR
cigs very late tonight into Wednesday morning, timing this is
challenging. Higher surface pressures over the central coast and
lower pressures over far northern California through Wednesday
will add a southerly component to the wind probably influencing
the marine layer cloud cover. Additionally, a lower level cyclonic
circulation over the offshore waters approaches the coastal waters
just west of the Bay area Wednesday.
Vicinity of ksfo...VFR, so far so good, is holding this evening.
Held onto 10z IFR cig forecast for 06z taf issuance. IFR prob
transitioning to MVFR cig early Wednesday morning, confidence is
low. MVFR cig may hold on through the morning as there is plenty of
stratus over the coastal waters combining with solid westerly flow
which may become gusty Wednesday afternoon and evening.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...IFR cigs tonight possibly trending over to
an MVFR early Wednesday morning, confidence in timing is low.
Plenty of stratus over the coastal waters combined with onshore
winds may keep MVFR cigs going through all of Wednesday morning.
Low confidence VFR returns Wednesday afternoon. Stratus is likely
to redevelop by early Wednesday evening.
Marine...as of 10:22 PM PDT Tuesday...surface high pressure will
be located over the central coast tonight through Wednesday resulting
in mainly light west to southwesterly winds over much of the coastal
waters with exception of the far northwestern coastal waters where
winds will still be northerly. Winds are forecast to weaken late
... Arena to Pigeon pt 10-60 nm
Public forecast: Rowe/rgass
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