Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 252136

Area Forecast Discussion
National Weather Service Sacramento CA
236 PM PDT Thu May 25 2017

Cooling continues into Friday with near to below normal
temperatures. Slow warming trend this weekend into early next
week. Isolated afternoon showers or thunderstorms possible over
the northern Sierra through the weekend.


.Discussion (Today through Sunday)...

Model analysis with water vapor imagery showed a broad trough area over
the west with the latest trough base moving through northern
California. Satellite imagery showed cloud cover from the delta
diminishing with other cloud cover remaining off the coast. Radar
returns across the area were clear. Latest surface pressure
gradient trends continue to weak and surface breeze has lessened,
but continues through delta influence areas.

Model forecasts are in good agreement with a shortwave positively
tilted trough moving across the Great Basin to the east, and the
trough will continue to exit the area by Friday. Southwest
oriented winds will continue to bring chances for marine layer
clouds into the delta and surrounding valley locations, but model
surface pressure gradients do not appear as strong as the past 24
hour period. Therefore, not expecting as strong of a breeze
overnight, but the delta will still see winds up to 20 mph.
Temperatures across the area will range between 5 and 10 degrees
below normal through Friday. In the vicinity of the passing
trough, mountain showers and thunderstorms are possible with some
mid level instability, although confidence at this point into
exact timing and formation is low.

Building ridge of high pressure from the eastern Pacific will
bring a return of near normal to slightly above normal
temperatures for Memorial Day weekend. Afternoon instability over
the mountains could lead to the development of an isolated
thunderstorm or two that could produce small hail and brief heavy
rain downpours.



A strong ridge will be in place to start the extended period and
that will bring hot temperatures. We will see highs near 100 in
the north Valley on Monday and Tuesday with 90`s elsewhere in the
Valley and 60-70`s in the mountains. Some instability in the
Sierra will lead to isolated thunderstorms during the afternoon
and evening but with little to no forcing chances are very low.
The ridge will be tracking east on Wednesday and we will start to
see some upper level energy spin off of an upper level low over
the Gulf of Alaska. Not expecting anything major with this system
but it could bring a few light showers or isolated t-storms to the
mountains. Wednesday would be the best chances but they still
look minimal at this time. This trough will also bring some
cooler temperatures as highs will be in the upper 80`s to mid 90`s
for the valley and 50-60`s in the mountains. A delta breeze will
keep the Delta areas a few degrees cooler.




VFR conditions expected this afternoon into the overnight. Gusts
to 25 knots will be possible in the Delta with 10-15 knot winds
expected elsewhere. Winds diminish to under 10 knots for the
overnight. Some low clouds around 3000 feet possible in the
Sacramento and Stockton areas between 12-18z Friday, local areas
of MVFR.





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