Scientific Forecaster Discussion
fxus66 kmtr 250545
Area forecast discussion
National Weather Service San Francisco Bay area
1045 PM PDT Wed may 24 2017
Synopsis...a cooling trend can be expected through Friday as
high pressure weakens and the marine influence increases. Minor
warming is then expected during the upcoming weekend into early
next week as high pressure returns to the West Coast.
Discussion...as of 08:09 PM PDT Wednesday...no big changes made
to this evening's forecast. Satellite continues to show marine
stratus along the central California coast. The Fort Ord profiler
indicates the marine layer is just above 2000 ft. Afternoon highs
were distinctly cooler across inland locations with many stations
at least 5 to 15 degrees cooler than Tuesday. Santa Rosa observed
one of the most prominent day-to-day changes: the high on Tuesday
was 84 but today it was only 64. The cooler temperatures were a
response to the departing ridge that had been parked over the West
Coast earlier this week, as well as a weak upper level low off
the California coast. The persistent onshore flow and overcast
skies helped to minimize the change in afternoon highs along the
Expect additional cooling through the end of the work week with
below normal temperatures for many locations. Coastal areas will
continue to see low clouds and experience highs ranging from the
middle 50s to 60s. Warmer weather will return for the Holiday
weekend as another ridge builds over the West Coast with 90s
returning to the southern Salinas valley as early as Sunday.
Previous discussion...as of 01:33 PM PDT Wednesday...only minor changes
to the ongoing forecast as unseasonably cool weather prevails into
the weekend with a gradual warm up next week.
Synoptically speaking an upper low remains off the coast spreading
mid and high level clouds over the region. At the surface, onshore
flow continues to keep low clouds and patchy fog along the coast.
The upper low and onshore flow led to much cooler temps around
the region today. 24 hour trend shows some impressive 24 hour
drops, 10 to 15 degrees colder in some spots. At 1 PM Santa Rosa
is 13 degrees colder today than Tuesday.
Only minor tweaks were made to previous forecast. Night and
morning clouds will continue with a marine layer 1,500 to 2,000
feet into the weekend. Patchy fog and drizzle will be possible,
especially along the immediate coastline. Milder temps will be
possible above the marine layer the next few nights, but not a
very strong thermal belt. As for daytime highs, temperatures will
continue to cool through Friday. Interior locations will drop to
very cool temps for late may with highs in the 70s to lower 80s.
Friday's forecast compare to climo is roughly 5-10 degrees below
Temperatures will begin to moderate and eventually warm over the
upcoming Holiday weekend as high pressure builds over the region.
The warmest of the three days will be Memorial Day, but mainly
over the interior. Persistent low clouds/fog will keep
coastal/Bay shoreline area cool. Highs on Monday will be 60s to
70s coast and 80s to lower 90s interior. Temperatures level off
next Tuesday and Wednesday.
Outside of some night/morning drizzle not forecasting any
noteworthy rain through the end of the month.
Aviation...as of 10:45 PM PDT Wednesday...the marine layer continues
to deepen this evening with lower level cooling eventually mixing out
the temperature inversion Thursday into Thursday night. Stratus
ceilings are forecast to be mostly MVFR category tonight and Thursday
morning. Also, spotty coastal drizzle or very light rain is possible
tonight and Thursday morning.
Vicinity of ksfo...S-SW winds 10-15 knots probably shifting to west-SW
tonight, timing is low confidence. MVFR cig developing tonight with
mixing out forecast by 17z Thursday.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...MVFR cigs tonight and Thursday morning.
Partial clearing is likely by late Thursday morning.
Marine...as of 10:31 PM PDT Wednesday...a newly developing weak
low pressure center will form just west of the Bay area Thursday
and remain nearly stationary through Friday. Southerly winds over
much of the coastal waters will persist tonight becoming locally
enhanced and gusty Thursday and perhaps again on Friday especially
along the Big Sur and Monterey Bay coastline. High pressure will
redevelop over the eastern Pacific just prior to the Memorial Day
weekend bringing a return to more typical afternoon and evening
onshore winds to the coastal waters and bays.
... Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm from 3 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm from 3 am
Public forecast: Rowe/mm
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