NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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000
FXUS66 KSTO 131644
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
945 AM PDT Fri Jul 13 2018

.SYNOPSIS...
Hot temperatures this weekend and into early next week. Monsoonal
moisture will occasionally bring a chance for showers and
thunderstorms to the higher elevations into next week.

&&

.DISCUSSION...
Update: Short wave oriented W-E over the central Sac Vly currently
lifting Nwd at about 15 kts and should be basically N of our CWA by
around 00z. Most of the C-G strikes associated with the vort max
just off the coast where this feature is expected to remain for the
rest of the day. Lack of dynamic forcing this afternoon (and lack of
solar heating due to thick monsoon moisture with bases 15-20 kft)
expected to limit, if not eliminate, thunder threat in our CWA. And,
the cloud cover should limit max temps a few degrees this afternoon
as well. GFS, NAM suggest a weak wave will develop in the SW flow
over Norcal after midnite and the elevated instability progs show
some TTs in our NErn zones later tonite which could suggest some
nocturnal showers or storms in the NE foothill and mtn zones. Will
look at those details in the afternoon package.

Most of the monsoon moisture should be pushing NEwd out of our CWA
on Sat and it will warm/heat-up a few degrees. However, this
morning`s models have not come in quite as hot as previous models,
especially in the N Vly for this weekend. This is due to a weak trof
moving moving across Norcal and the Pac NW suppressing 5H heights
over our CWA. In the wake of this trof, 5H heights rebuild over
Norcal extending the heat through the middle of next week. Another
monsoon push may occur later next week as the high repositions
itself over the climatologically favored Four Corners area this time
of year and the mid level flow turns SEly.   JHM

.Previous Discussion...
Upper ridge of high pressure over the southwest U.S and weak low
over the Pacific producing light southeast flow over most of
California. This southeast flow has brought Monsoon moisture over
the region and this has translated into some mid and high cloudiness
over the north state. So far no precipitation has been reported over
the CWA but a few echos are showing up on Radar just south of the
forecast area and off the Bay Area coast and lightning detection is
indication very isolated thunderstorms with this offshore activity.
Models all showing a weak disturbance pivoting up the north coast
this afternoon so a slight thunderstorm threat over the coast range
seems reasonable.
Stability progs showing another area of instability over the
northern Sierra so keeping afternoon thunderstorm threat for there
today as well. Overall airmass does not change much today but
cloud cover should bring a drop in daytime temperatures by a
degree or two. Upper ridge pushes back to the northwest on
Saturday bringing a bit of warming most areas. Much of the central
valley will continue to top 100 degrees with the northern
Sacramento valley pushing 108. The exception will be the delta
influenced areas where the highs will remain in the 90s thanks to
a moderate delta breeze. Another shortwave disturbance may bring
isolated thunderstorms to the northern mountains while monsoon
moisture continues to bring a threat of thunderstorms to the
northern Sierra.

Offshore upper low pushes into the Pacific Northwest on Sunday.
Model consistency on details have varied over the last couple of
runs so will need to monitor future runs to analyze for possible
northern mountain shower threat. Southwest flow aloft on Sunday
should push Sierra thunderstorm threat southward a bit but could
still see isolated Sierra storms south of Tahoe. Have warmed
temperatures up a bit on Sunday but model variance has made this
less certain. Warming temperatures a better bet on Monday as high
pressure amplifies over the west coast. High temperatures are
forecast to hit 110 in Redding Monday. Have therefore issued a
heat advisory for the northern Sacramento valley and surrounding
foothills for Sunday, leading in to the warmest day, and Monday
when temperatures are expected to be the hottest of the week. The
ridge should also bring enough stability for a temporary end in
the Sierra thunderstorm threat.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Strong high pressure will maintain hot weather across the region
next week. The Sierra Nevada south of Lake Tahoe will see a
slight chance for late-day showers and thunderstorms. Highs
across warmest portions of the forecast area will be around 5-10
degrees above average.
&&

.AVIATION...

VFR conditions the next 24 hours with SCT-BKN150. Isolated
thunderstorms over higher terrain, mainly 21Z-03Z. Local southwest
wind 15-25 kts in the Delta.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Sunday to 8 PM PDT Monday for Central
Sacramento Valley-Clear Lake/Southern Lake County-Motherlode-
Mountains Southwestern Shasta County to Northern Lake County-
Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-
Shasta Lake Area / Northern Shasta County-Southern Sacramento
Valley.

&&

$$
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