Area Forecast Discussion
Issued by NWS Reno, NV

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451
FXUS65 KREV 170614
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
1014 PM PST Thu Nov 16 2017

.UPDATE...

We have updated to expire the Flood Watch. The Winter Storm
Warnings remain in effect for the Tahoe area above 7000 feet and
Mono County above 8000 feet. Although precipitation intensity has
decreased...the actual cold front and a secondary wave aloft will
drop south overnight. This should provide for a burst of snow
across northeast CA and northwest NV into the early overnight
hours before moving south through the rest of CWA by shortly after
daybreak Friday. It is not out of the question for some areas
north of Susanville and Gerlach to receive up to 4 inches of snow
late tonight. This should not be wide spread...so we will not plan
on any advisories at this time. Also...gusty winds will continue
on Lake Tahoe overnight. Conditions will be borderline for a Lake
Wind Advisory...but the strongest winds should end shortly after
daybreak Friday.

&&

.PREVIOUS DISCUSSION... /Issued 823 PM PST Thu Nov 16 2017/

UPDATE...

Precipitation in the northern Sierra and far western NV continues
to decrease as the primary moisture tap drops south through
central CA this evening. Forcing is decreasing as this feature
slides south as well. That should lead to a slight decrease in
precipitation overnight in the southern/central Sierra...but still
impressive totals along the crest in Mono County. With the upper
level jet starting to slide east...spill over precipitation
should be far less in southern Lyon and Mineral counties late
tonight as opposed to that which fell in far western NV earlier
today.

A second push of precipitation associated with the main cold front
will drop south through the night and impact areas of northwest
NV and northeast CA first before sliding south of I-80 by
daybreak. This will bring another burst of precipitation along
with falling snow levels...so even though many areas north of I-80
have seen little in the way of precipitation the last few
hours...it is not over yet.

We have adjusted pops to reflect this burst along the front later
tonight and early Friday...and lowered snow levels just a little
by daybreak.

The lower elevation rain earlier today has resulted in rises on
many streams and the upper portions of mainstem rivers. So far the
only flooding report we have is due to ponding in a low lying area
on Centerville Lane in Douglas County. We will let the Flood Watch
continue until 10 pm this evening then drop it as much of the
primary precipitation will end by that time. The precipitation
later tonight may cause brief spikes in flow before the snow
levels fall.

Reservoir managers will increase flows on the Truckee overnight
and into Friday to lower water levels in flood control space and
to make room for anticipated additional rainfall next week.

PREVIOUS DISCUSSION... /Issued 203 PM PST Thu Nov 16 2017/

SYNOPSIS...

An atmospheric river continues to bring rain and high elevation
snow to the region with the main moisture band slowly moving
south tonight. A cold front will move through the region tonight
lowering snow levels and bringing light showers. Periods of gusty
winds will continue into Friday morning. Drier weather returns for
the weekend followed by additional chances for wet weather next
week.

SHORT TERM...

Significant rain has already fallen with rivers, creeks, and streams
around the region responding. While rapid rises took place, it
appears the risk of flooding is low. However, smaller creeks and
streams coming out of the eastern Sierra could still come close.
Other areas that remain a concern include locations with poor
drainage and recent burn scars. We received a report of minor rock
slides in the Walker River Canyon near the Chris Fire, however
Highway 395 was not impacted with the debris only on the shoulder
of the road.

Winds remain tricky as strong winds remain at ridge level, but are
only surfacing in a few valley locations. It`s likely that the heavy
precipitation is dampening out the wind speeds, but as rainfall
weakens in intensity, it is possible that gusty winds will once
again surface.

The main moisture plume associated with the ongoing atmospheric
river event is slowly sliding south, with the heaviest precipitation
anticipated in Alpine and Mono counties this evening. The main upper
level low and associated cold front will also finally slide south
tonight. The bulk of the precipitation will have already fallen by
the time snow levels begin to fall, however, travel impacts will
most certainly be possible across mountain passes. The other concern
tonight is the potential for freezing temperatures to turn any
liquid on area roadways to ice by Friday morning. Tonight`s lows
will largely depend on wind and cloud cover and it is possible that
some locations will remain mild due to these factors. If it were
me...allow extra time for your commute Friday morning in the event
roads are slick.

Frontogenesis and lift are decent along the front, but instability
is fairly shallow and deeper moisture is waning. It`s likely the
front will bring light snow showers mainly northward of a Plumas
State Park to Lovelock line. Up to a couple of inches of snow
looks possible for these areas tonight into Friday morning with
lingering showers possible in the eastern Sierra as well. The
storm finally exits the region Friday night with clearing skies
leading to a cold start Saturday morning. -Dawn

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

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

For next week, the large scale pattern will remain active, but the
storm track is shifted slightly north into the Pacific Northwest,
for now. High pressure across the southwest will deflect the storms
to the north of the Sierra and western Nevada, but any changes in
position or magnitude of the ridge will allow the storms to be
directed south into the Reno-Tahoe area. ECMWF and GFS both show a
large trough setting up off the coast of British Columbia, which
will allow several waves to impact the Pacific Northwest coast and
possibly as far south as the Interstate 80 corridor. Those same
operational simulations show a decent moisture tap extending across
the eastern Pacific with this trough. which would increase potential
for warmer and wetter storms.

Takeaways:
* This weekend: Clear drains and gutters, and prepare for
  potentially more rain next week.
* Those with hydrologic interests should pay particular attention to
  any storm potential for next week, especially after the current
  storm.
* Have Thanksgiving travel plans? No guarantees the weather will be
  quiet. Plan on rain if you will be venturing north into the
  Pacific Northwest. Always carry chains, extra water, and food when
  traveling through the mountains.

-Edan

AVIATION...

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.

Winds remain fairly strong at ridge level with sustained winds in
the 40-65 kts range, however, winds are only surfacing at a few
valley locations. Wind speeds may pick up this afternoon as
precipitation begins to wane, but stronger winds will be spotty.

Precipitation should remain mostly as rain for the Reno-Tahoe area
terminals, though KTRK and KTVL may turn to a rain/snow mix
tonight. At that point, the deeper moisture will have exited the
region, so any accumulation would be minimal.

At KMMH the most impactful rain will continue into Friday morning
with a rain/snow mix possible later tonight.

Something to watch out for is any standing water on runways freezing
overnight behind the cold front. Freezes are likely for all Sierra
terminals, with KRNO/KCXP more uncertain due to winds and cloud
cover overnight. -Dawn

&&

.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning until 4 AM PST Friday above 7000 feet in
     NVZ002.

CA...Winter Storm Warning until 4 AM PST Friday above 8000 feet in
     CAZ073.

     Winter Storm Warning until 4 AM PST Friday above 7000 feet in
     CAZ072.

&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno



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