Scientific Forecaster Discussion
fxus66 kmtr 291605
Area forecast discussion
National Weather Service San Francisco Bay area
905 am PDT Mon may 29 2017
Synopsis...turning mostly sunny inland this afternoon with clouds
persisting along the coast. Temperatures to remain near or
slightly below normal through Wednesday then nudging slightly
warmer by Thursday and Friday with continued dry conditions.
Discussion...as of 9:05 am PDT Monday...no forecast updates
planned for this morning. Its a cloudy start for most of the
valleys with the marine layer around 2000 feet deep. The sfo to
SAC gradient is already 3 mb so breezy west winds will continue to
increase this afternoon keeping any warmth around the Bay in
check. The flow aloft remains cyclonic with moderate surface
pressure gradients and a marine layer in place through at least
midweek. This all points to continued near or slightly below
normal temps for the last few days of may. Some morning drizzle is
possible again Tuesday morning near the coast and coastal hills
with persistent onshore flow and some weak synoptic lift.
Mid and long range ECMWF solution keeps the district dry with what
looks to be a pretty seasonable weather pattern. No Big Warm-ups
noted with strong pressure gradients off Cape Mendocino keeping
persistent NW flow in place over the coastal waters and along the
Previous discussion...as of 3:00 PM PDT Monday...widespread clouds
overnight for many spots with the marine layer still at 1500 feet
plus a moderate onshore flow. Similar to yesterday, most spots are
in the 50s and should see lows mostly in the upper 40s to the mid
50s by day break.
Today will be a near repeat of yesterday with clouds forecast to
slowly burn-off toward the coast by late in the morning. Yesterday
turned out to be a bit of a surprise in the East Bay with a very
late transition to sunny skies. Models hint at the possibility
again today which could keep temps running a bit lower than
forecast. Outside of that, no issues anticipated with highs
expected to range from the 60s at the coast up to the 70s and
lower 80s inland. A few locations well inland could get into the
mid to upper 80s. Tonight will feature another round of patchy fog
and drizzle mainly near the coast.
Synoptically an upper level low will works it's way to the British Columbia
coastline while an associated trough advances to the West Coast.
Ahead of the main trough, a weak shortwave will move through on
Tuesday which will start to deepen the marine layer and provide a
degree or two of cooling. More substantial cooling (especially
inland) can be expected on Wednesday as the main trough moves
onshore. At the same time enough instability and associated
moisture could lead to a few showers late Tuesday into Wednesday,
although latest guidance has backed off a bit. Winds will also
pick up on Wednesday as the onshore flow increases. Westerly winds
of 10 to 20 mph with local gusts to 30 mph can be expected.
A weak ridge of high pressure will start to rebuild into our
region going to the end of the week. Highs will return back to
near normal levels.
Aviation...04:25 am PDT Monday for 12z tafs...widespread clouds
with solid marine layer and mainly IFR conditions. Clouds will be
slow to clear today and the immediate coast may not clear at all.
Gusty onshore flow later today. Cigs return tonight.
Vicinity of ksfo...IFR cigs through 19z with VFR there after.
Guidance still shows strong west winds this afternoon with gusts
up to 25 or 30 kt. Cigs return early tonight.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...IFR cigs through this morning. Cigs will
gradually lift, but conf is low that any clearing will occur at
kmry more likely at ksns. Winds will increase Monday afternoon
out of the west at 10 to 20 kt. Cigs return early tonight.
Marine...as of 08:55 am PDT Monday...gusty northerly winds will
continue over the coastal waters and eventually over the bays
today as the surface pressure gradient tightens. Steep winds waves
and fresh swell will cause rough and hazardous seas. Winds will
decrease mid week as a weak frontal system moves through the
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt 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...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...mry Bay from 12 PM
Small Craft Advisory...sf Bay from 12 PM
Public forecast: rww
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