Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 240536
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1036 PM PDT MON MAY 23 2016
.SYNOPSIS...A weak low pressure system will bring a slight chance
of showers and a thunderstorm or two to our region tomorrow.
Temperatures will be seasonably cool, but gradually warm later in
.DISCUSSION...AS OF 9:50 PM PDT Monday...Low clouds have filled
in very quickly over much of the area this evening. Even KCCR and
KLVK airports now reporting low cigs. An upper level low center
located over the Bay Area will move southeast away from the area
beginning Tuesday. This low produced plenty of positive vorticity
...upward vertical motion and deep atmospheric cooling around the
A high May sun angle...surface warming and steepened lapse rates
led to a few areas (well inland) of surface based instability in
the ballpark of 600-800 j/kg CAPE with near zero convective
inhibition. A lone and slow moving thunderstorm developed close
to the Santa Clara and Stanislaus county border in the mid-late
afternoon then gradually it drifted SE across western Stanislaus
A few isolated sprinkles are possible tonight. On Tuesday the low
center will once again set the stage for a few showers possibly an
isolated thunderstorm. Present forecast looks good.
.PREVIOUS DISCUSSION...as of 2:00 PM PDT Monday...A few echoes
have been indicated on the KMUX radar today especially off the
coast. Over the past hour a narrow band of rain has steadily moved
toward the Monterey coastline. Issued an update to the forecast to
boost PoPs generally from Monterey southward. Have also seen a few
returns across eastern Santa Clara County although would expect
most of that has not reached the ground.
This time of year usually features warm readings with far inland
spots in the 80s and possibly 90s. Thanks to a cool NW flow aloft
with a longwave trof stretching through our region, temps are
continuing to run below to well below normal. Within the trof, a
weak disturbance will rotate through today which may bring a few
showers and even a stray thunderstorm or two to higher elevation
spots -- especially the North and East Bay. Rainfall amounts
should be light...generally less than .05".
A second weak system will rotate through near the base of the trof
on Tuesday. This will bring another slight chance for showers and
possible thunderstorms to the region. Best chances again look like
the North and East Bay. San Benito County will likely see a few
showers as well due to their closer proximity to the low.
A ridge of high pressure will start to build off the coast for the
second half of the week which will lead to a gradual warm-up along
with dry conditions.
.AVIATION...as of 10:36 PM PDT Monday...Low clouds continue to
fill in quickly over the area this evening. Expect patchy drizzle
or sprinkles overnight into Tuesday morning. MVFR cigs with areas
IFR cigs tonight then gradual clearing Tuesday. Isolated -SHRA
possible in the area due to lingering instability Tuesday.
Vicinity of KSFO...MVFR cig tonight clearing by late Tuesday
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...IFR cigs and light westerly winds tonight.
Cigs improving to MVFR by late Tuesday morning. MVFR cigs likely
returning Tuesday evening.
.MARINE...as of 9:14 PM PDT Monday...An upper level low over the
bay area tonight will move southeast from tuesday through mid-
week. high pressure over the eastern pacific will build over
northern california mid to late week and result in increased
northwesterly winds and building seas.
PUBLIC FORECAST: Canepa/Bell
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