Area Forecast Discussion
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FXUS66 KSTO 210554 CCA

Area Forecast Discussion
National Weather Service Sacramento CA
1030 PM PDT Sun May 20 2018

Afternoon and evening thunderstorms possible over higher terrain
much of this week. Seasonal temperatures continue across the


Update: Upper level cyclonic circulation along the NWrn CA coast
dropping Swd along the coast with closed upper level low forming
over the Srn half of CA by midday Mon. Cyclonic flow around the low
will continue an unstable air mass over the mountains, with the
activity moving Wwd and perhaps into the Sierra Foothills Mon
afternoon or evening. Over the Nrn SJV, thickening mid clouds Mon
afternoon/evening may lead to some sprinkles/light showers. NAM
BUFKIT forecast soundings show mid cloud deck thickening from 10-35
kft Mon evening and would not be surprised to find some showers

Not as strong of an onshore flow or Delta Breeze as yesterday so
stratus not expected to intrude into the Vly as yesterday.  JHM

.Previous Discussion...
A low pressure area will move southward overnight through the
central part of California. This may trigger some showers over the
western slopes later at night as it moves towards Southern
California. Unstable air is still forecast for the region with most
of the activity continuing to remain over the mountains and
foothills. Cyclonic flow around the low may bring a few showers or
isolated thunderstorms into the valley in the evening hours on
Monday and mainly over the eastern end of the valley from around
Chico southward.

On Tuesday the low will move northeast into the Great Basin with
easterly flow continuing to bring moisture westward back over
Northern California. Continued showers and thunderstorms for the
mountains and foothills is expected. This might also be the best
chance for activity to move over the valley...mainly north of

The low over the Great Basin begins to lift northeast on
Wednesday and winds aloft will shift southerly over the region.
Less activity is expected compared to the prior two days. Most of
the activity should stay over the mountains but the north end of
the valley may continue to be under the threat of thunderstorms.

Decent flow will continue through the Delta the next few days and
temperatures for most locations with remain near seasonal normals
with the exception of the north end of the valley which will warm
to around 90 degrees the next couple of days.



Closed upper low off the California coast Thu into Fri, tracks NE
through Interior NorCal Sat. This will continue a threat of
showers and afternoon/evening thunderstorms over the foothills and
mountains, and possibly in the Northern Sacramento Valley. By
Sunday, low is progged into Oregon with a decreased threat of deep
moist convection over the CWA. High temperatures forecast to be
near to slightly above normal through the extended period with 80s
in the Central Valley, and mostly 60s to 70s for the mountains
and foothills.



Upr trof ovhd dvlps into upr low ovr Cntrl CA tngt into Mon. VFR
conds ovr Intr NorCal nxt 24 hrs exc wdly sct MVFR/IFR conds poss
in shwrs and aftn tstms omtns. Lcl MVFR/IFR conds poss in ST vcnty
Delta into Srn Sac Vly btwn 10z-18z Mon. Lcl SW-W sfc wnd gsts up
to 25 kts in Delta til arnd 08z tngt, and to 20 kts in Srn
Sac/Nrn San Joaquin vlys til abt 04z.


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