Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 181000

Area Forecast Discussion
National Weather Service Sacramento CA
300 AM PDT Fri Aug 18 2017

Temperatures near to above normal through the forecast period
with a threat of afternoon/evening mountain thunderstorms.


.DISCUSSION (Today through Sunday)...
Strong high pressure from the EPAC extends inland over Interior
NorCal and will result in highs today near or a few degrees
warmer. High temperature of 109 in Redding yesterday set a new
record. Record high for today at KRDD is 110 and although 109 is
forecast, this record could be tied or broken. Most all other
areas will be well below record values today, but upwards of 5 to
10 degrees above normal. Flow through the Delta has been strong
overnight, but will trend down during the morning hours. Marine
layer is about 500 feet shallower than 24 hours ago due to
increased subsidence. As a result, max temperatures around Delta
influenced areas will likely be similar or a few degrees warmer
today. Elevated instability progs showing increased 700-500 MB MU
CAPE and TT values over the higher terrain of the Sierra Nevada
and Coastal range this afternoon to support isolated thunderstorm

Heights/thicknesses trend down over Interior NorCal through the
weekend as upper troughing deepens over the area. As a result,
onshore flow increases along with depth of marine layer. High
temperatures cool to near normal by Sunday into Monday. Afternoon
thunderstorms will continue to be possible over the higher
terrain of the Sierra Nevada Saturday and Sunday, expanding to
include the northern and coastal mountains Monday.



An upper level low set up over SoCal will help to push moisture
north into NorCal for the start of the extended period. This will
bring the chance for Mountain thunderstorms on Monday and Tuesday
during the afternoon and evening hours. There will be plenty of
moisture in the region to bring scatted clouds to the Valley both
Monday and Tuesday also. The upper level low will still be hanging
around on Wednesday but sounding profiles don`t look quite as
favorable for convection and that should limit t-storm activity.
The upper level low will be working east on Thursday as a trough
drops south into the PacNW. The latest Euro run has lined up
nicely with the GFS keeping the main energy well to our north over
Canada. This will bring dry conditions to round out the extended
period. Not expecting anything crazy with temperature throughout
the forecast as they will be plus or minus a few degrees from



VFR conds ovr Intr NorCal nxt 24 hrs exc lcl MVFR/IFR poss in ST
vcnty of Delta til arnd 17z. Isold aftn tstm poss ovr hyr trrn of
Siernev and Cstl mtns btwn 21z-01z. SWly sfc wnd gsts to 25 kts
poss thru Delta til 16z and agn aft 00z.



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