Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
300 am PDT Wednesday may 6 2015
Synopsis...quiet weather conditions are expected today with
temperatures running a few degrees below seasonal averages. There
is a slight chance of showers and thunderstorms Thursday and Friday
..mainly over the mountains as an upper level system moves in
from the north. Dry weather conditions and slightly warmer
temperatures return for the weekend as the system shifts inland.
Discussion...as of 3:00 am PDT Wednesday...satellite imagery
shows that low clouds have formed along the San Francisco
peninsula coast...around portions of the San Francisco Bay...and
around the Monterey Bay. The northerly surface pressure gradient
has increased and is currently just over 5 mb between acv and sfo.
This gradient is forecast to increase further today. The tight
northerly gradient should prevent extensive inland stratus
penetration this morning...thus...mostly sunny skies with highs
ranging from the lower 60s at the coast to the 70s inland.
Meanwhile...and upper level low is working its way south from British
Columbia and is prognosticated to be over northern California by Thursday
morning. This upper low is expected to generate shower chances
across the eastern portions of California and the Great Basin...however
as this low moves south and west...there is an increased chance
for showers across mainly the southern and eastern portions of the
district on Thursday and Friday. Given the proximity to the upper
low center...thunderstorms are also a possibility for these areas.
The upper low is forecast to begin moving to the east on Friday
and reaching southern Nevada and northern Arizona by Saturday.
Weak high pressure will briefly build over the West Coast by
Sunday for warmer temperatures. Another trough is then prognosticated to move
across the West Coast by early next week bringing cooler weather to
Aviation...as of 10:40 PM PDT Tuesday...the northerly gradient
remains strong at over 6 mb from acv-sfo. This will keep Bay area
terminals free of stratus through tonight. Patchy low clouds
are expected to return overnight to Monterey Bay area terminals
but elsewhere should remain mostly clear. Light southwesterly
winds anticipated through the overnight hours with moderate and
gusty onshore flow returning Wednesday afternoon.
Vicinity of ksfo...VFR conditions expected through the forecast
period. Moderate onshore flow will continue through tonight.
Strong and gusty onshore flow expected to pick up Wednesday
afternoon with sustained wind speeds of 15 to 20 knots and gust
to near 30 knots possible.
Sfo bridge approach...similar to ksfo.
Monterey Bay area terminals...MVFR ceilings expected through tonight
with clearing anticipated around 18z-19z Wednesday. Light to
moderate winds expected through the night with moderate and
locally gusty winds anticipated Wednesday afternoon with
sustained winds around 15 knots with gust over 20 knots possible.
Marine...as of 2:21 am PDT Wednesday...gusty northerly flow will
continue over the coastal waters high pressure builds over the
Pacific northwest. Gale force winds will persist over the outer
waters north of Pigeon Point. The strong winds will produce
hazardous conditions with steep wind waves and fresh swell. Wind
and waves will gradually decrease over the weekend.
... Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
glw...pt Arena to pt Reyes 0-10 nm
glw...pt Arena to pt Reyes 10-60 nm
glw...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...sf Bay south of the Bay Bridge from 1 PM
Small Craft Advisory...Monterey Bay from 1 PM
Public forecast: Sims
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