Area Forecast Discussion
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FXUS66 KSTO 200947

Area Forecast Discussion
National Weather Service Sacramento CA
247 AM PDT Sun May 20 2018

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

A shortwave trough has been passing through northern California
yesterday evening and this morning. After diurnally-driven
convective activity had tapered off, isolated thunderstorms
developed late yesterday evening in the vicinity of Redding /
Shasta Lake. This nocturnal activity has since pushed
northeastward. Elsewhere, a moderate to strong onshore gradient
along with elevated marine layer has resulted in a healthy stratus
push inland. Expect a bit of stratus to push into the southern
Sacramento and northern San Joaquin Valley toward sunrise.

The upper trough will continue to deepen today, forming a closed
low over central / southern California by Monday and shifting
eastward into the Great Basin on Tuesday. While we do expect some
convective development again this afternoon, it will likely favor
the Shasta / Trinity / Mendocino ranges, along with southern
Cascades. Showers and thunderstorms then become more widespread
along the Sierra again Monday through Wednesday.

Temperatures will fluctuate over the next several days but will
generally be within a few degrees of normal. Locally warmer
weather is projected along the northern Valley Monday and Tuesday,
as north winds develop and bring adiabatic compressional heating
to those locations.




GFS/ECMWF in better agreement lifting upper low over the eastern
Pacific toward the region late in the week. This will keep a
daily threat of showers and afternoon thunderstorms over the
foothills and mountains. EC tracks low inland across NorCal late
in the weekend while GFS now lifts the wave across the PacNW.
This leads to uncertainty as to how much precip is possible over
the weekend. For now forecast keeps precip chances confined to the
foothills and mountains. Temperatures expected to remain close to


Upr trof ovr NorCal with Wly flow alf. Mnly VFR conds nxt 24 hrs
exc wdly sct MVFR/IFR conds poss omtns in shwrs/tstms and lcl
MVFR/IFR cigs in ST poss vcnty of Delta into Srn Sac Vly thru 18Z.
Lcl SWly sfc wnd gsts to 30 kts cont thru Delta til with lcl gusts
15-20 kts srn Sac Vly and nrn SJ Vly 20Z-04Z Mon.


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