Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
443 am PDT Tuesday Apr 28 2015
Synopsis...look for cooler temperatures today and tomorrow due to
a deeper marine layer plus a moderate onshore flow. Temperatures
will rebound for Thursday and Friday to well above normal.
Discussion...as of 3:00 am PDT Tuesday...looking at the satellite
loop this morning certainly gives the impression of a typical June
gloom morning with widespread clouds both at the coast and into
adjacent valleys. Did receive multiple reports of drizzle and fog
in the area so those were both added to the grids for the morning
hours. Biggest story for today will be the cooler conditions
compared to the warm readings on Monday. Surface gradients really
tell the story with sfo-SAC now onshore around 3.5 mb which is
nearly 2 mb over yesterday. Even the north-S component has changed in
favor of a westerly flow by dropping from 5.5 mb to around 2.5 mb.
Highs will range from upper 50s to upper 60s for most coastal
spots to mostly 70s for inland areas. In some places it will be a
drop of 15 to 20 degrees compared to yesterday. Similar conditions
are forecast for Wednesday.
On Thursday a dramatic increase in temperatures is forecast as the
offshore flow kicks in helping to produce warmer and drier air.
European model (ecmwf) guidance continues to be the hottest although NAM values are
trending toward similar values. Widespread 80s can be expected
inland with upper 60s to upper 70s at the coast. Northeasterly
winds of 15 to 25 miles per hour look likely for the North Bay hills which
will elevate fire weather concerns. Offshore winds will continue
into Friday although they will likely moderate a bit. Highs will
still be well above normal although coastal spots should see a sea
breeze influence by the afternoon.
Temperatures will return closer to normal over the weekend as a
weak shortwave trough moves to the coast while a moderate onshore
push continues at the surface. Highs will remain with 60s at the
coast and 70s inland.
Looking to next work week..onshore surface flow will remain in
place while the 500 mb flow becomes weak northwesterly. Dry
conditions will continue across our County Warning Area with the main storm track
focused on Alaska and British Columbia.
Aviation...as of 10:41 PM PDT Monday... low base stratus deck
intrusion this morning leading to widespread IFR to MVFR ceilings in
coastal valleys. Fort Ord profiler shows layer from 200ft through
1200ft this morning. Seems to verify with observation of ovc002-ovc003 at
various sites as of 430am. Looking like a slow burn late this
morning with lingering few/scattered low clouds through the day at most
taf sites. Onshore gradient tightens later today and lead to
breezy onshore flow. Gusts into the low 30s are possible along the
coast including at ksfo.
Vicinity of ksfo... IFR ceilings through 16z. MVFR ceilings through 17-19z.
Lingering few/scattered low clouds after 19z. Onshore winds pick up late
morning and become rather gusty by the early afternoon. Peak gusts
into the lower 30kt range possible.
Sfo bridge approach... similar to ksfo.
Monterey Bay area terminals...IFR ceilings. Expecting the stratus clouds
to mix out by late Tuesday morning but most likely poised to move back
in early Wednesday evening. Occasionally breezy onshore winds.
Marine...as of 04:33 am PDT Tuesday...moderate to strong
northwest winds will continue over the coastal waters through the
next several days. Occasional gale force gusts will be possible
beginning Tuesday evening. Building northwest swell through
midweek. Hazardous conditions from squared seas will also be
possible in some local areas on on Wednesday.
... Pt to pt pinos 0-10 nm from 11 am
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm from 2 PM
Small Craft Advisory...Monterey Bay from 2 PM
Small Craft Advisory...sf Bay north of the Bay Bridge from 2 PM
Small Craft Advisory...sf Bay south of the Bay Bridge from 2 PM
Public forecast: Bell
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