Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 212137

Area Forecast Discussion
National Weather Service Sacramento CA
237 PM PDT Fri Jul 21 2017


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



Water vapor imagery continues to indicate a steady stream of dry
air across northern California under southwest winds aloft.
Visible satellite imagery shows some smoke activity around the
Detwiler fire, but areal expansion northward along the Sierra
foothills and mountains seems to be lesser as compared to previous
days. Temperatures this afternoon are running a few degrees warmer
than the early afternoon yesterday.

High pressure will continue to build and allow warming
temperatures for the valley and surrounding foothills heading into
this weekend. With little overnight relief due to warm low
temperatures, a heat advisory has been issued for the northern
Sacramento valley and surrounding foothills.

A weak subtle trough will develop off the coast Saturday into
Sunday with some height falls aloft. This may bring some Sierra
crest thunderstorms south of Highway 50 Sunday afternoon and
Monday afternoon. Currently the GFS is the most aggressive model
as far as convective development, however other forecast models
seem to be keeping the main threat of thunderstorms to the east of
the Sierra crest. Confidence is low as to thunderstorm development
and timing, but the next few model runs should be able to capture
the situation better as models resolve the building high pressure
and the developing shortwave trough in the eastern Pacific.



Offshore upper low progged to move inland Tuesday although models
differ with progression rate. Progs however showing better
potential for showers/thunderstorms over the mountains Tuesday and
thus have bumped up POPs for those areas. Cooler temperatures
continue Tuesday. Weak baggy upper troughing aloft continues
through the remainder of the week resulting in drier weather with
a slight upward trend in temperatures.



SWly flow alf with VFR conds ovr Intr NorCal nxt 24 hrs exc isold MVFR
conds poss in smk vcnty of Detwiler Fire in Mariposa Cnty. Lcl SW
sfc wnd gsts to 25 kts poss ovr hyr mtn trrn aftn/eve and thru
Delta ovngt.



Heat Advisory from noon Saturday 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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