Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 221615

Area Forecast Discussion
National Weather Service Sacramento CA
915 AM PDT Mon May 22 2017

NorCal`s first triple digit heat of the season will continue for
portions of the Central Valley today and Tuesday. Cooling
trend begins Wednesday with near to slightly below normal temperatures
by Friday. Isolated late day showers or thunderstorms possible
over portions of the mountains Tuesday and Wednesday.


.Discussion (Today through Thursday)
High amplitude upper ridge over the EPAC extends inland resulting
in well above normal temperatures over Interior NorCal. Triple
digit heat expected in portions of the Central Valley today with
hottest readings forecast in the Northern Sacramento Valley.
Marine layer is around 1300 ft deep and flow through the Delta is
only around 15 kts so cooling influence into the Valley will be
nill today. Models showing some afternoon instability over the
Sierra Nevada but available moisture looks too limited for deep
moist convection.

Upper ridging gets suppressed slightly over NorCal Tuesday as
northern portions of it progress into the Great Basin, ahead of
short wave system tracking towards the PacNW. Little change
expected in max temps Tuesday with possible exception of slightly
more Delta breeze influence into the Southern Sacramento Valley.
High temperatures Tuesday continue above the century mark in the
Northern and Central Sacramento Valley. Mid to upper 90s expected
for the Southern Sac/Northern San Joaquin portions of the Central
Valley. Slight increase in available moisture and instability
Tuesday over the Sierra Nevada, south of US-50, may result in
isolated afternoon showers or thunderstorms.

Marine layer deepens Tuesday night as upper low approaches and
onshore flow increases. Models showing strong flow through the
Delta developing overnight Tuesday into Wednesday. Weak cold
front progged to drop from the PacNW across northern portions of
CA on Wednesday as short wave system digs into the Great Basin and
expands westward. This will begin a cooling trend Wednesday that
continues through the remainder of the week. Slight chance of
showers or thunderstorms possible over the Shasta and Coastal
mountains Wednesday afternoon into evening.

Cooling continues Thursday with more stable AMS. 80s expected
throughout the Central Valley with 70s in the Delta and
foothills, and mainly 50s to 60s in the mountains.



Troughing over the area on Friday will lead to cooler
temperatures, especially near the Delta with onshore flow. Ridging
builds back in for Memorial Day weekend with warming
temperatures. Continued onshore flow will keep Delta and southern
Sac Valley noticeably cooler than the northern Sac Valley where
afternoon highs will top out in the mid to upper 90s. Enough
instability around with weak disturbances in the flow to warrant
the chance for showers and thunderstorms across the mountains, but
valley should remain dry.



VFR conditions the next 24 hours. Variable winds less than 10 kts
at valley TAF sites.




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