Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 192047
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
147 PM PDT Fri May 19 2017

.SYNOPSIS...

Very warm temperatures will increase the rate of snow melt this
weekend and early next week leading to flooding near creeks and
streams flowing out of the Sierra. The Walker River through the
Mason Valley and Yerington is expected to reach major flood stage
early next week with record levels possible. Some flooding is
also likely for the upper portions of the Carson and Truckee
River systems. Visit http://weather.gov/reno to see the latest
hydrologic warnings and advisories.

&&

.SHORT TERM...

Temperatures will heat up this weekend as high pressure builds
across the West Coast. These above average temperatures will
lead to accelerated snow melt and flooding concerns along creeks
and streams out of the Sierra as well as main stem rivers
extending into western Nevada. See the hydrology section below
for details on flooding potential particularly for the high
likelihood of major to near record flooding for the Walker River
through Mason Valley early next week.

Otherwise, benign weather is expected through the weekend with
high temperatures warming to the lower to mid 80s across western
Nevada with mid 70s for Sierra valleys. A weak shortwave trough
will drop south across the region Sunday afternoon. This may
develop some cumulus across the Tahoe Basin but the best potential
for showers and isolated thunderstorms will exists mainly across
the Sierra in Alpine and Mono counties on Sunday and Monday
afternoons. Fuentes


.LONG TERM...Tuesday through Friday...

Above average temperatures and snow melt flooding will continue
next week. Creek and small stream flooding is also expected for
some areas. For details, see the hydrologic section below.

Recent computer model simulations show a signal for thunderstorms
over the Sierra Tuesday afternoon as the offshore low-pressure
circulation draws increasing moisture northward. Weak southeasterly
steering flow could anchor some storms over the Sierra so they could
be slow movers. Confidence remains low because computer models often
struggle with the track and timing of these weak offshore lows. This
is not a classic moisture surge, but even moderate rain rates could
locally enhance flooding if they happen to occur upstream or over
areas of snow melt flooding. This could develop Tuesday
afternoon/evening and again Wednesday afternoon/evening.

There are some indications that a low pressure system will approach
the Pacific Northwest Thursday which would begin to increase the
southwest flow across the region for the end of the week.
Thunderstorms could have a better push east off the Sierra into
western NV Thursday. JCM

&&

.Aviation...

VFR conditions through Saturday. Expect afternoon cumulus buildups
and a slight chance for thunderstorms over the Sierra Sunday and
Monday. On Tuesday there is a chance for thunderstorms to start over
the Sierra in the afternoon and then spread east into the Sierra
front range in the evening. Away from any thunderstorms, VFR
conditions will prevail with light winds and mostly clear skies. JCM

&&


.HYDROLOGY...

Warming temperatures this weekend through the Memorial Day weekend
will accelerate snowmelt across the Sierra. Overnight low
temperatures in the higher elevations are likely to remain above
freezing as well...and this will enhance snowmelt.

This increased snowmelt will cause significant rises in many area
small streams and rivers from southern Mono County through the
eastern Sierra and into Sierra and Plumas counties. These higher
flows are likely to produce overbank flows in the smaller streams.
Farther downstream...flooding possibilities will increase for some
of the major basins.

Minor flooding is possible by early next week for the Carson Valley
area while major to near record flooding is likely for the Walker
River through Mason Valley. On the East and West Walker rivers minor
to moderate flooding is likely for areas including the Antelope and
Smith valleys. Higher flows are also likely below Weber
Reservoir...but the expected extent is unknown at this time.

Some minor overbank flow is possible along the Truckee River with
bank erosion possible from Truckee downstream to Reno. The extent of
any flooding is far less certain on the Truckee. Reservoirs on the
Truckee can be managed to limit the extent of any minor flooding.

Make sure to check the most recent forecasts and observations if you
live near a stream or river...or plan to hike or camp near any
streams or rivers. Remember that snowmelt flows can be highest in
the evening and overnight in the smaller streams.

&&

.REV Watches/Warnings/Advisories...
NV...Flood Watch from Sunday morning through Tuesday evening
     NVZ002-003.

CA...Flood Watch from Sunday morning through Tuesday evening
     CAZ071>073.

&&

$$

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



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