Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 011014
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
314 AM PDT SAT OCT 1 2016

.SYNOPSIS...
A weather system will bring unseasonably cool temperatures, Valley
rain, mountain snow, and possible thunderstorms Sunday into early
Tuesday. Drier weather expected by the middle of next week.

&&

.DISCUSSION...
Clear skies prevail across interior Northern California, behind a
dry upper level front that passed through yesterday. Looking
upstream, an unseasonably deep upper low is centered off the
Vancouver Island coast and rapidly dropping southward. We`ve
already seen a fair bit of synoptic cooling associated with this
system, and temperatures across the region are running up to 10
degrees cooler than yesterday.

Dry weather will continue today, with high temperatures reaching
the 70s across the Valley, and 50s and 60s over the mountains.
These forecast highs are 5 to 10 degrees cooler than normal.

The aforementioned upper low will quickly move toward the region,
moving inland near the CA/OR border Sunday. This isn`t the most
favorable track for a widespread rain for NorCal. But this system
brings quite the cool airmass and instability, and should be
efficient in wringing out precipitation. Isolated
thunderstorms are possible Sunday afternoon and evening. Snow
levels are expected to rapidly drop to around or below 6000 ft by
Sunday afternoon, with a few inches of snow possible at pass
level. Given the long stretch of dry weather we`ve experienced,
and traditionally heavy weekend traffic over the mountains, major
travel headaches will be possible with even minor snow
accumulations.

Computer models have been trending wetter with a northwesterly
wave moving through NorCal Monday afternoon and night. Confidence
isn`t strong with this secondary system, but we did bump up our
precipitation forecast rather substantially to match model trends.

Dang

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

Middle portion of the week looks dry under relatively flat upper
level high pressure ridge. Daytime temperatures warm each day but
still remain a few degrees below normal. GFS shows a moderate northerly
surface gradient from MFR to SAC of about 9mb so expect breezy
north winds on Wednesday although upper level support is not
ideal. Surface gradient weakens on Thursday as the upper ridge
axis shifts eastward into the Great Basin. A weak upper trough
moves through the Pacific Northwest on Friday bringing a threat of
showers to the northern most state. Most areas should see a slight
cooling. Temperatures warm again slightly on Saturday under weak
high pressure.
&&

.AVIATION...

VFR conditions expected all TAF sites next 24 hours. Increasing clouds
Sunday with precipitation chances after noon. Winds generally
below 15 knots except 15-20 knots through the delta.

&&

.STO Watches/Warnings/Advisories...
Winter Weather Advisory from 11 AM Sunday to 5 AM PDT Monday for
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

&&

$$



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