Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service San Francisco Bay area
1049 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 08:34 am PDT Tuesday...morning temperatures
mostly in the upper 40s to middle 50s with extensive stratus well
into the valleys. Marine layer running around 1500 feet with
strong onshore flow. Pressure gradient sfo to SAC nearly 2 mb
this morning and winds at suu gusting over 20 miles per hour.

Weak cold front approaching north coast should dissipate as it
moves onshore late tonight and early Wednesday. Stratus will
persist this morning then clearing back to the coast this
afternoon. Marine stratus should push inland quickly
tonight...but dissipate faster Wednesday as flow begins to
parallel the coast and GOES offshore by Wednesday night.

Still on track for about a 10 degree jump in temperatures
Thursday as winds are mostly offshore...particularly during the
morning hours. 850 mb temperatures warm to about 18c and offshore winds
only light to moderate...so not expecting record warmth...but
above normal readings nonetheless.

Biggest concern from an impacts standpoint is the expected
increase in north winds over interior North Bay mountains late
Wednesday night and Thursday morning. This will bring drier
conditions and increased fire weather concerns...though rains
from late last week should help mitigate impact somewhat.

Current forecast look to be on track with no changes planned this
morning.

&&

Previous discussion...as of 3:00 am PDT Tuesday...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 10:45 am PDT Tuesday...low level clouds continue
to impact coastal locations and areas around the bays...yet have
seen clearing over the inland valley locations. Should continue to
see improvement in the next few hours region wide...while areas
around the Monterey Bay may only see brief clearing this
afternoon. Onshore flow will increase today as the surface
pressure gradient tightens with gusts at or above 20 knots possible.
Winds diminish slightly late tonight with low level clouds likely
to return late this evening and persist into Wednesday morning.

Vicinity of ksfo...IFR ceilings through about 19z. Lingering few/scattered
low clouds through the afternoon with an increase in onshore
winds. Gusts above 20 knots likely this afternoon/evening. Early
return of low level clouds possible tonight...moderate confidence.

Sfo bridge approach...clearing has already taken place this
morning...otherwise similar to ksfo.

Monterey Bay area terminals...LIFR/IFR ceilings through 18z-20z.Burn-
off expected inland with kmry potentially only seeing brief break
in ceilings this afternoon. Onshore flow increases this after with
breezy conditions into the evening. Early return of low level
clouds possible by late evening...moderate confidence.

&&

Marine...as of 10:45 am PDT Tuesday...moderate to strong
northwesterly winds will persist over the coastal waters through
midweek. Occasional gale force gusts will be possible beginning
this evening...especially over the northern offshore waters and
off of the Big Sur coast. Building northwest swell through
midweek. Hazardous conditions from squared seas will also be
possible in some local areas on Wednesday.

&&

Mtr watches/warnings/advisories...
... 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: kbb
aviation/marine: rgass

Visit US at weather.Gov/sanfrancisco

Follow US on facebook, twitter, and youtube at:
www.Facebook.Com/nwsbayarea
www.Twitter.Com/nwsbayarea
www.Youtube.Com/nwsbayarea

National Weather Service Glossary of Abbreviations