Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 261014
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
314 AM PDT Wed Jul 26 2017

.SYNOPSIS...
Near normal temperatures today, then hot weather returns Thursday
into early next week. A slight chance of afternoon mountain
thunderstorms today, and then again over the weekend.

&&

.DISCUSSION...
Very slow moving closed upper level low has now pushed inland...
hovering over Mendocino County early this morning. Most of the
nocturnal activity has remained in Oregon, while mostly clear
skies prevail across much of northern California. A healthy marine
layer and moderate onshore breeze are helping to cool the usual
locations near the Delta.

The upper low will slowly drift northeast today, gradually
weakening as it does. The best chance of convection today will be
near Lassen Park and areas north and east of the park. Otherwise,
dry weather will continue across the region. Very warm
temperatures are expected this afternoon, with highs reaching the
mid 90s to around 102 degrees across the Valley, and 70s to 90s
over the mountains.

High pressure over the Desert Southwest will expand toward NorCal
Thursday and into the weekend, bringing mainly dry weather and a
return to hot temperatures. Triple digit heat is likely across the
Valley during this timeframe. Another surge of monsoonal moisture
and associated thunderstorms will be possible over the mountains,
especially toward the weekend.

Dang

&&
.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)

Light upper flow over the region Sunday under large high pressure
system over the western U.S. Forecast daytime highs are expected
to come in several degrees above normal. With very light upper
flow it is difficult to gage amount of monsoon moisture that will
make it into the area. GFS paints afternoon convective precip
over the northern Sierra while ECMWF remains mainly dry. Have
slipped in a slight chance of afternoon thunderstorms to cover
uncertainty. Very little change expected on Monday so kept
temperatures and thunderstorm chance area nearly unchanged. Model
confidence fades towards the middle of next week as models differ
on handling of upper low pushing in off the Pacific. For now, have
kept temperatures and Sierra thunderstorm threat similar to
Monday until models come into better alignment.

&&

.AVIATION...


VFR conditions the next 24 hours across interior NorCal. Isolated
afternoon thunderstorms over northern mountains. Winds generally
below 10 knots except up to 25 knots through the delta.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$


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