Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 231031

Area Forecast Discussion
National Weather Service Sacramento CA
331 AM PDT Tue May 23 2017

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


Clear skies across interior NorCal early this morning. Current
temperatures are pretty similar to readings from 24 hours ago and
generally range from the 40s to around 50 in the mountain valleys
to the 60s and 70s elsewhere. The marine layer continues to vary
in depth from around 1-1.5K feet helping to sustain the Delta
Breeze where the reading at Travis AFB is in the upper 50s.

Little change in temperatures compared to Monday are expected
across the region today as the upper ridge moves overhead.
However, a stronger Delta Breeze is expected to bring slight
cooling to the Carquinez Strait and Fairfield areas and faster
cooling to the Sacramento region this evening. Isolated
thunderstorm activity will be possible late today in the Sierra
to the south and east of the forecast area.

Marine layer deepens tonight as upper low approaches and onshore
flow increases. Models showing strong flow through the Delta
developing overnight into Wednesday with cooler overnight minimums
extending further inland with the Delta Breeze.

Cold front progged to drop from the PacNW into far northern
California Wednesday before stalling out. The developing upper
trough and stalled front may provide the focus for a few late day
thunderstorms across the northern mountains.

The bigger impact for the area will be the significant cooling
trend that commences Wednesday and continues through Friday. Many
areas are expected to be 15-20 degrees cooler Thursday and Friday
compared to today! Additionally, breezy southerly winds will
affect much of the region.


Ridging builds back in for the holiday weekend with warming
temperatures. Warmest temperatures expected across northern Sac
Valley where highs will approach the upper 90s by Sunday and
Memorial Day. Those with outdoor plans should keep an eye on the
forecast as activities may be impacted by the heat. Onshore flow
will keep decent delta breeze going, so expect much cooler
conditions in that region and possibly into the Sacramento area.
Weak moisture return and instability under dirty ridge may allow
for a few showers and thunderstorms to develop across the Sierra
Saturday and Sunday afternoons, but low confidence in just how
widespread the activity will be. For now, have introduced slight
chance pops, mainly south of Tahoe. Short wave approaching the
coast will shift ridge off to the east for Monday and Tuesday,
bringing additional chances for convection across the Sierra.
Again, low confidence in this but something to watch going
forward. CEO


VFR conditions the next 24 hours at valley TAF sites. Winds
generally 10 kts or less.




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