Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 161039

Area Forecast Discussion
National Weather Service Reno NV
239 AM PST Thu Nov 16 2017

A moderate to strong atmospheric river will impact the Sierra and
western Nevada through today with significant rain and higher
elevation snowfall, as well as periods of gusty winds. A cold
front will move through the region tonight and Friday morning,
bringing lower snow levels and a chance for a light snowfall in
some lower valleys. Drier weather returns for the weekend.



One more wave of moderate to heavy precipitation is hitting the
northern Sierra this morning as a moderate to strong atmospheric
river (AR) remains pointed at that area. Rainfall rates are also
moderate to heavy into a few areas in the immediate lee of the
Carson Range as well with good moisture transport in the AR.
Overall in the past 24 hours, between one and 2.5 inches (up to 3
to 3.5 inches near crest) of precipitation has fallen in the
northern Sierra. Out into western Nevada away from the immediate
east side of the Carson Range (including Washoe Valley and far
West Reno/Verdi), general rainfall amounts have been between
0.25" and 0.50". Heavier precipitation rates should sag south
into Alpine and Mono Counties by later this morning and into the
afternoon as the AR is pushed south as an upper low approaches the
Pacific Northwest coast.

Regarding snow levels, they remain near or slightly above 7000
feet this morning in the northern Sierra per observations. Earlier
snowfall on Donner Summit has cleared to just wet roads with
temperatures in the low to mid 30s. However, snow levels are a bit
variable with a few locations holding onto slushy roads below 7000
feet in the Tahoe Basin per CALTRANS cams. Farther south into Mono
County, snow level remain around 8500-9000 feet as precipitation
has been much lighter there outside of the AR. The struggle
between weak advection of warm air in the AR and lift and heavier
precipitation causing cooling will continue until precipitation
lightens up later this morning; thereafter, snow levels could
creep up a bit in the Tahoe area.

BOTTOM LINE FOR SNOWFALL/WINDS: Snow level variations could
result in higher totals in Lassen/Plumas counties down to 5500
feet and the Tahoe basin down to around 6500 feet by the time the
snow ends Friday morning. Periodic increases in winds east of the
Sierra during periods of lighter precipitation support maintaining
advisories today; however, with more than isolated high winds no
longer anticipated today high wind warnings have been downgraded.

Tonight and Friday morning, a cold front pushes through most of
the region as the upper low off the Pacific Northwest coast moves
inland. Good frontogenesis/lift is indicated in GFS/NAM simulations
along the front; however, instability is shown to be rather shallow
south of a Susanville to Lovelock line with the core of the upper
low tracking near the California/Oregon/ Nevada border. Therefore,
any showers should remain light for most of the region. -Snyder

.LONG TERM...Saturday through Thanksgiving weekend...

Saturday and Sunday continue to look dry and warm with light winds
and minimal cloud cover.

For Monday-Tuesday, atmospheric river forecasts from the ensembles
are learning toward a coastal decaying system with some inland
propagation for the northern Sierra and northwest NV. GEFS/NAEFS has
really trended away from a impactful system by building a ridge over
CA/NV and deflecting most of the moisture into the Pacific
Northwest. ECMWF has maintained a quick moving system through the
Sierra and western NV but recent runs suggest a weak to run of the
mill Sierra storm.

The big Wednesday travel day looks fine for those driving over the
Sierra, south through the eastern Sierra to Vegas/SoCal and east
along I-80. Flights in and out of the region may be impacted by some
mountain wave activity, but nothing unusual at this time. Those
traveling north into Oregon, and the NW California coast are looking
at some light to moderate rainfall.

Thanksgiving Day is where the biggest model differences arise. AR
tools keep the impactful weather off to the north and GEFS/NAEFS
maintain the ridge over CA/NV. ECMWF does bring a potent storm into
the region late on Thanksgiving day, which if it occurs, would lead
to rain/snow travel impacts for the Sierra passes and US-395 in
Lassen, western NV and Mono county. Brong



Atmospheric River system will continue to impact the region today
with mountain waves, low level wind shear and periods of heavy rain.
Impacts for Reno-Tahoe terminals should start to wane by tonight,
with impacts to KMMH persisting into Friday morning.

At this time, winds have diminished quite a bit, through wind should
restrengthen later today. Peak surface gusts should stay below 45
kts, through a few locations may briefly exceed 45 kts. Ridge top
winds are down into the 25-50 kt range, but should climb back up to
to 40-65kts this afternoon.

Precipitation should remain mostly as rain for the Reno-Tahoe area
terminals, through KTRK and KTVL may turn to a rain/snow mix or
briefly all snow early this morning.

At KMMH the most impactful rain should begin after 18z today with
snow possible later tonight. LLWS will continue to be a problem
today. Brong


.REV Watches/Warnings/Advisories...
NV...Flood Watch through this evening NVZ002-003.

     Wind Advisory until 4 PM PST this afternoon NVZ003-005.

     Winter Storm Warning until 4 AM PST Friday above 7000 feet in

     Wind Advisory until 4 PM PST this afternoon NVZ001-004.

CA...Flood Watch through this evening CAZ071>073.

     Winter Storm Warning until 4 AM PST Friday above 6000 feet in

     Wind Advisory until 4 PM PST this afternoon CAZ070.

     Winter Storm Warning until 4 AM PST Friday above 8000 feet in

     Winter Storm Warning until 4 AM PST Friday above 7000 feet in



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