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000 
FXUS66 KSTO 221030
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
330 AM PDT Sat Jul 22 2017


.SYNOPSIS...

Hot and dry weather today. Widespread triple heat across the
valley this weekend. A little cooler next week. Slight chance of 
Sierra thunderstorms Sunday afternoon and into early next week.

&&

.DISCUSSION...
High pressure aloft over the southwest U.S. bringing fair skies 
to the CWA this morning with temperatures running just a bit 
higher that 24 hours ago. Upper ridge is forecast to back eastward
over the state today bringing a warm up of several degrees. The
northern Sacramento valley could see daytime highs today near 110
degrees. Will leave the heat advisory up as is with heat risk 
criteria still being met. Sub tropical moisture and instability 
appear to remain south of the forecast area today so have left 
any shower or thunderstorm out of the forecast for now. Models in 
good agreement in moving a weak upper low in off the north coast 
on Sunday. More onshore flow and a slight airmass cooling will 
bring slightly cooler temperatures. Bigger impact may be push of 
sub tropical air northward up the Sierra crest. GFS shows 
instability along the crest as well so an afternoon slight 
thunderstorm chance along the Sierra crest seems a reasonable 
forecast threat. Upper low digs a bit farther southward on Monday.
Southeast flow aloft will continue to bring moisture and 
instability up the Sierra crest so thunderstorm threat continues. 
More airmass cooling should drop daytime highs most valley 
locations down to below the century mark. Upper low remains 
centered around the north coast on Tuesday bringing still more 
cooling. Daytime highs next Tuesday are forecast to drop to near 
or even a little below normal. Upper level southerly flow will 
continue to bring afternoon and evening thunderstorm threat up the
Sierra and Cascade crest. 

&&
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

Computer models have come into better agreement with the handling
of the offshore upper low, with the GFS and ECMWF now pushing the
system inland on Wednesday. As such, thunderstorm chances should
continue across NorCal mountains through midweek. Drier weather
ensues toward the end of next week with a slight warming trend and
forecast temperatures a few degrees warmer than normal.

Dang

&&

.AVIATION...

Mainly VFR conditions the next 24 hours across interior NorCal,
except reduced visibilities in smoke near the Detwiler Fire. Winds
will remain light today, except gusts to 25 kt near the Delta and
over higher terrain.

Dang

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 9 PM PDT Sunday for Central 
Sacramento Valley-Mountains Southwestern Shasta County to 
Northern Lake County-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Shasta Lake Area / Northern Shasta 

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