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Area forecast discussion 
National Weather Service San Francisco Bay area
456 PM PDT Wednesday Jul 1 2015

Synopsis... monsoonal moisture and energy will result in
isolated showers and thunderstorms for the southern counties
this evening and possibly overnight. A cooling trend will
begin tomorrow and continue into the weekend as temperatures
approach normal values.

&&

Discussion...as of 3:00 PM PDT Wednesday... California is
between a 595dm dome of high pressure over the Great Basin and a
581dm low pressure system west of Baja California California in a typical
summertime monsoonal pattern. Monsoonal moisture is resulting in
impressive precipitable water values of between 125% of normal
for most of our forecast area to over 200% of normal for portions
of central and Southern California. Precipitable water values
range from around 1.1 inches over the North Bay to 1.4 in southern
Monterey County... to around 1.8 off of Los Angeles and San Diego.
The most easily identifiable feature of this abundance of middle to
upper level moisture is the increase in cloudiness across the
region. These clouds are predominately based at around 15000 feet.

Visible satellite shows a well defined mesolow moving from the
southeast towards the northwest and into the southern portion of
our County Warning Area this afternoon. This middle level feature has increased
instability around it and triggered thunderstorms on the north
and west flank over the last 24 hours. Several lightning strikes
have been reported already in southern Monterey and San Benito
County this afternoon from this feature. Kmux radar shows a light
band of returns around the center of this feature however most of
the precipitation is falling from 15000 feet or more and may only be
resulting in virga. Thus far... only a few hundredth have been
reported beneath these returns. Have updated the forecast to
include a slight chance of thunderstorms over Santa Cruz and and
Santa Clara County into the evening and possibly further northward
into tonight. Additional energy and moisture will advect into the
region overnight tonight and... due to the elevated nature of this
convection... could result in a few nocturnal flashes of
lightning. Short to medium term models are hinting at the
possibility of additional convection Thursday and even Friday
morning however uncertainty is still high over the
timing/placement.

Temperatures today are a mixed bag... with many locations running
a few to several degrees cooler than yesterday and a much smaller
portion as warm or even warmer today. The warmest area was in and
around the east and South Bay interior... where triple digit
temperatures are already being observed as of 3pm. Temperatures
are forecast to cool off several more degrees for tomorrow and
then gradually cool towards normal temperatures into the weekend.

Drp

&&

Aviation...as of 4:56 PM PDT Wednesday...for 00z tafs. Showers
and isolated T-storms are rotating offshore over Monterey County
at this time but isolated activity remains possible for areas
south of San Jose. Hard to get a gage on the marine layer but it
appears very shallow offshore at this time. Low confidence on
return but for now will show some late night stratus at Bay area
terminals with expectation that any morning ceilings will mix out
by 16-17z.

Vicinity of ksfo... VFR with high clouds this evening and a
light to moderate westerly seabreeze. Low confidence for ceilings
returning by morning.

Ksfo bridge approach...similar to ksfo.

Monterey Bay area terminals...isolated showers and T-storms this
evening then some low stratus to push back inland overnight.

&&

Climate...record highs for July 1 for selected locations.

Sf Bay area................July 1
Kentfield.................103/1996
San Rafael.................99/1991
Napa......................103/1972
San Francisco..............92/1991
sfo Airport................99/1985
Oakland downtown...........92/1984
Oakland Airport............90/1985
Richmond...................97/1985
Livermore.................110/1950
Mountain View..............97/1985
San Jose..................102/1985
Gilroy....................108/1972

Monterey Bay area............July 1
Monterey...................96/1985
Santa Cruz.................99/1970
Salinas....................85/1996
Salinas Airport............88/1991
King City.................105/1985

&&

Marine...as of 4:41 PM PDT Wednesday...high pressure across the
coastal waters will maintain light winds and seas through the
forecast period. A weak disturbance will pass by on Thursday
bringing southwesterly winds and a chance of showers and
thunderstorms to the region.

&&

Mtr watches/warnings/advisories...
... Advisory...North Bay area... East Bay area
and the Santa Clara Valley until 9 PM.
Small Craft Advisory...sf Bay until 9 PM

&&

$$

Public forecast: drp
aviation: rww
marine: CW
climate: Bell



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