Area Forecast Discussion
Issued by The National Weather Service
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FXUS66 KSTO 252206

Area Forecast Discussion
National Weather Service Sacramento CA
306 PM PDT Fri May 25 2018

Scattered showers and isolated thunderstorms this evening across
the area. Afternoon and evening thunderstorms possible mainly over
higher terrain into next week. Cooler than normal temperatures
continue across most of the region through Saturday, warming to
well above normal for early next week.


A robust closed upper low is currently centered just off the San
Francisco Bay Area, slowly making its way toward the coast. Strong
diffluence out ahead of the low led to widespread showers across
the region today. A few tenths of an inch of rain has been
reported across the CWA, locally up to an inch along the Sierra
and northern Sac Valley. The band of heaviest rainfall and
thunderstorms has shifted north to the far northern portions of CA
and NV. Substantial cloud cover and low level moisture have kept
temperatures unseasonably cool this afternoon. As of this writing,
temperatures across the Valley are only in the mid 50s to mid 60s
across the Valley, and 30s to 40s over the mountains. These highs
are roughly 15 to 20 degrees cooler than normal.

The aforementioned rain activity will begin to shift southward
again this evening into Saturday as the upper low moves inland.
These showers will gradually dissipate as this occurs, though
afternoon showers and thunderstorms will still be possible over
the mountains Saturday. Given recent model trends, we canceled the
Winter Weather Advisory for snow over the high Sierra. That being
said, a quick inch or two of snow accumulation will still be
possible over those locations.

An upper level ridge will build into California Sunday into
Monday, bringing a rather dramatic warming trend. By Memorial Day,
high temperatures will be in the mid to upper 90s across the
Valley. This could bring a moderate heat risk, mainly to sensitive
groups like infants and the elderly.




The ridge that will bring warmer weather to the end of the
holiday weekend will be pushing east to start the extended period.
Warm temperatures are expected to continue on Tuesday though. A
trough will then drop south into the region for the middle and end
of the week and that will bring cooler weather dropping highs to
near or just below normal. There will also be chances for t-storms
in the higher elevations during the afternoon and evenings. It
does look to remain isolated due to low CAPE values and not very
favorable soundings.



MVFR/IFR will continue for the northern terminals with generally
VFR for the southern terminals. OVC 2000 to 3500 feet in the north
with OVC 3500 to 5000 feet for the south. Rain showers move in
during the evening mainly for the northern terminals and diminish
as it pushes southward. Conditions improve during the morning
Saturday. Winds are expected to remain 10 knots or below.



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