Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
419 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 4:15 am PDT Wednesday...another tough forecast
and low conf. Despite a rather north-S gradient skies are clear over
the coastal waters...but low ceilings have developed inland. Patchy
MVFR ceilings can be expected through much of the early morning with
middle-late morning burn off. The exception would be mry Bay where
ceilings will last the longest. Gusty onshore winds expected again
today. Overall conf is medium to low.
Vicinity of ksfo...ksfo had MVFR ceilings the past few hours...but
have now scattered. Will have prevailing VFR...but tempo MVFR as ceilings
may drift in again from the west. Nearby ceilings should clear out 17-18z.
Gusty onshore winds again this afternoon. Gusts up to 30 knots poss.
Sfo bridge approach...patchy ceilings remain over the approach but do
show some signs of scattered like ksfo.
Monterey Bay area terminals...MVFR ceilings through 19-20z. Gusty sea
breeze push again this afternoon.
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
Visit US at weather.Gov/sanfrancisco
Follow US on facebook, twitter, and youtube at: