Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 210557
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1057 PM PDT FRI MAY 20 2016



.SYNOPSIS...
Cool through the weekend with scattered showers, possible
thunderstorms, and mountain snow. Below average temperatures with
a threat of mountain showers through the middle of next week.

&&

.DISCUSSION... An active afternoon and evening over Norcal with
plenty of showers...thunderstorms over the valley and heavy
mountain snow. Snow amounts above 5500 feet appear to have been
over a foot in many locations with a measured 13 inch amount at
Kingvale. Thunderstorms produced up to dime size hail in a few
spots along with brief heavy rain...isolated valley rainfall
amounts up to 0.50 inches. Mountain rainfall was generally
0.50-1.50 inches. Activity is diminishing late this evening. The
exception is shower cluster over eastern Shasta county. Will
expire winter wx adv at 11 pm not expecting much more over the
Sierra. Although Lassen could pick up a few more inches overnight.

.PREVIOUS DISCUSSION...
Scattered shower activity continues across NorCal, mainly over
the mountains and north of Interstate 80 in the valley. Radar has
shown some heavier showers this afternoon mainly between Yuba City
and Chico which impacted Hwy 99 earlier. There have been reports
of lightning with those heavier showers, but it has been cloud to
cloud lightning...no cloud to ground strikes, yet. Snow showers
over the Sierra are impacting mountain travel with travel delays
and chain controls on Interstate 80. Current snow levels are
around 5000 to 5500 ft with snow falling at Blue Canyon. Check
CalTrans road conditions before you head over the Sierra this
evening and into the weekend.

The center of the low bringing this weather is over NorCal this
afternoon and will linger over us through Saturday before
weakening and moving northeastward on Sunday. Thus, the cooler
temperatures (around 10-20 degrees below normal) will persist
along with the chance of showers and thunderstorms through
Saturday. On Saturday, snow levels will still be around 5000-5500
ft with an additional 1-3 inches of snow expected.

By Sunday, lingering showers still possible, but should remain
near or north of Interstate 80 along with a slight warming of
temperatures by about 5 degrees.

On Monday, another trough swings into NorCal bringing a second
dose of showers and thunderstorms to much of our CWA. Daytime
highs will still be about 8-15 degrees below normal, but snow
levels will rise a bit becoming 6000-7000 ft. Not as much moisture
expected with this trough so snow/rain accumulations will be
light except for areas where strong showers/thunderstorms develop.
&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Forecast confidence decreases through the extended forecast
period as models show increasingly divergent solutions. GFS/GEM
maintain long wave troughing next week with varying strength of
short waves moving through. ECMWF starts to shift long wave east
Wednesday with increasing heights over NorCal into Friday. With
little confidence in any solution, we made minimal changes to the
forecast.

Dang

&&

.AVIATION...

Upper level system will remain over Northern California through
Saturday. Mainly VFR conditions expected for the TAF sites,
except local MVFR conditions in scattered showers or
thunderstorms. MVFR to locally IFR conditions across higher
elevations. South to west winds 5 to 15 kts with local gusts up
to 25 kt this afternoon.


&&

.STO Watches/Warnings/Advisories...
none.

&&

$$



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