Flood and Hail in California, June 11, 2017

Area Forecast Discussion
National Weather Service San Francisco Bay Area
149 PM PDT Sun Jun 11 2017

.SYNOPSIS...An unseasonably cool trough will bring showers and
thunderstorms to portions of Northern California today. As the
system exits to our east on Monday, a warming and drying trend is
forecast through the remainder of the workweek. Near normal
temperatures return Wednesday. Above average temperatures arrive
Thursday through next weekend.

&&

.DISCUSSION...as of 01:45 PM PDT Sunday... We are continuing to
monitor the southward progression of an unseasonably cool/deep
upper low. Remote sensing data shows the center of the upper low
over the Northern Sacramento Valley early this afternoon, with
scattered to widespread convective rain showers rotating around
the center of this circulation. Satellite imagery shows deeper
convective development occuring on the eastern and western flanks
of the upper low (over the coastal range and Northern Sierra
Nevada), with lightning strikes now detected over these areas, the
closest being just to the northeast over Lake county.

Forecast models project that the core of the upper low will dig
further southward today, advecting colder air into our region from
the north which will further destabilize the atmosphere aloft.
This will cause the deeper convection to shift over the North Bay
and portions of the East Bay through the remainder of the
afternoon and evening. Precipitation will be confined to areas
that see the deeper convection this afternoon and limited to a few
to several hundredths. In addition, isolated embedded
thunderstorms could bring locally heavier rainfall, small hail,
lightning, and gusty winds. A few weaker showers may drift
southward into the South Bay/Monterey Bay region this evening or
overnight. Breezy to gusty onshore winds will persist through the
remainder of today and tomorrow, especially along the immediate
coast, near coastal gaps such as near KSFO, and over the higher
terrain surround our valley communities.

The aforementioned upper low will exit the region tomorrow and be
replaced by high pressure from the eastern Pacific. This high
pressure system will promote a gradual warming and drying trend,
with near normal temperatures by mid week, and above normal
temperatures for Thursday through next weekend. Between today and
Friday, temperatures increase 4-8 degrees along the immediate
coast, 10-20 degrees for inland locations, and up to 30 degrees
for the further inland valley location. The warmest inland valley
locations could hit triple digits temperatures Friday through
Sunday.

&&

.AVIATION...As of 10:30 AM PDT Sunday...An approaching upper level
low will bring increased instability and clouds to the area this
afternoon and overnight. The best chance for showers remains
across the north and eastern terminals. Have removed some of the
thunderstorms from SFO south. Not enough moisture. Biggest issue
today will be winds. Strong Northwest winds are expected through
the evening, tapering off only somewhat overnight.

Vicinity of KSFO...VFR/MVFR. Gusty westerly winds today and
probably most of tonight. Thermal trough reaches the SF Peninsula
later this morning into the afternoon with vicinity showers.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Gusty westerly winds likely developing
by later this morning. Tempo MVFR cigs in a few showers later this
afternoon and overnight. MVFR cigs expected this evening and
overnight with a few lingering showers possible.

&&

.MARINE...as of 08:30 AM PDT Sunday...A cold upper level low will
track into northern California today bringing increasing
northwest winds and a slight chance of showers and thunderstorms
to the coastal waters, mainly north. High pressure and dry weather
then return early to mid next week with northwest winds remaining
moderate to strong.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Mry Bay
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...SF Bay

&&

PUBLIC FORECAST: DRP
AVIATION: Sims
MARINE: Sims

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