Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 212151

Area Forecast Discussion
National Weather Service Reno NV
251 PM PDT Sun May 21 2017


Warm temperatures will increase snow melt this week, leading to
flooding near some 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. Some
minor flooding is also likely for the upper portions of the
Carson and Truckee River systems.


.Short Term...

Spring warm up is in full effect this week. Temperatures in the
higher elevations, Slide Mountain at 9650` for example, only
dropped to 41 degrees this morning. Above freezing overnight low
temperatures combined with daytime high temperatures running 7,
to as much as 15 degrees above average, will significantly
increase snowmelt runoff and bring renewed flooding this week.
Small creeks and streams will be running cold and high the next
few days along with varying degrees of flooding along the main
stem rivers in the region. The area of greatest concern continues
to be the main stem of the Walker River through the Mason Valley
near Yerington. For more information about the flood outlook see
the Hydrology section below.

There will be a few thunderstorms in the region the next few days,
but coverage and intensity are expected to be limited. A passing
short-wave will create a slight chance for thunderstorms today in
the eastern Sierra and White Mountains in Mono County. Slight
warming aloft Monday is expected to keep development limited to a
few towering cumulus clouds, with no thunderstorms expected.

By Tuesday chances again increase with afternoon thunderstorms
possible along the Sierra crest from around Lake Tahoe south into
Mono County. Weak afternoon zephyr wind on Tuesday could push the
storms into west central Nevada, most likely staying south of
Reno/Carson metro areas. On Wednesday stronger afternoon winds
and a little more thunderstorm coverage is possible in western
Nevada as a low pressure along the California coast begins to move
inland increasing instability and adding some forcing to the
equation. -Zach

.LONG TERM...Thursday through Sunday...

A broad upper-level trough will remain across the region mid-week
and will provide a little cooler and near average temperatures by
the weekend. The trough will allow our surface pressure gradient and
winds aloft to increase midweek with breezy to windy conditions
continuing into Thursday afternoon. Hazardous boating conditions and
travel restrictions for high profile vehicles from crosswinds are
possible. Have continued to reduce precipitation chances as the
westerly flow appears to be rather dry with only a few isolated
shower possible near the southern Oregon border on Friday. As the
trough departs, high temperatures could rebound a few degrees by the
end of the weekend and into the following week as a shortwave ridge
builds across the region. Fuentes



Light north winds and VFR conditions for most areas the next few
days. Slight chance of thunderstorms today in Mono County.
Increasing stability tomorrow should limit convection to towering
cumulus clouds with chances for afternoon thunderstorms
increasing again on Tuesday, mainly along the Sierra crest and far
western Nevada south of US50. -Zach



Warm temperatures through the middle of the week will accelerate
snowmelt in the Sierra. The increased snowmelt will produce varying
levels of impacts next week. Anything from minor and nuisance
flooding of small creeks and streams to major flooding for the
mainstem Walker River through the Mason Valley.

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.


* Major flooding is likely for the mainstem Walker River through
  Mason Valley. Current projections show similarities to the
  flooding that occurred in 1983 and 1986. The Walker River could
  begin reaching into minor flood stage as early as Tuesday with an
  estimated short range crest Fri-Sat with continued flows in excess
  of Major Flood stage.

* Impacts to Mason and Yerington are largely dependent upon
  unpredictable channel breaches along the river. If a breach does
  AND YERINGTON. In any event, now is the time to act; it may be too
  late once the waters rise above moderate flood stage.

* Minor/Moderate flooding is possible on the East and West forks of
  the Walker River. This includes Antelope and Smith valleys. Higher
  flows are also likely below Weber Reservoir but the expected
  extent is unknown at this time.


* Minor flooding impacts possible from Lake Tahoe to Truckee. Most
  of the minor flooding impacts will be confined to areas right
  along the river which may impact some riverfront yards, basements,
  campgrounds, and bike paths.

* The flows along the remainder of the Truckee River will remain
  high, swift, and cold! These conditions can always be dangerous
  and it is recommend to keep a safe distance from the river.


* Broad minor flooding in the the southwestern Carson Valley between
  Centerville and Genoa.

* Minor Flood stage as early as Tuesday night with daily peaks
  occurring each night through the week. Flows will remain cold and
  swift on all portions of the river.


* Best estimates for flows this week coming out of unregulated
  eastern Sierra creeks and streams are likely to be 2-2.5 times
  current flows with smaller creeks likely to see 3 times current
  flows. Peak flows from this heat episode likely Wednesday or
  Thursday night.

* Creeks and streams will run fast and very cold, bringing the
  risk of hypothermia for those without protective gear. Flood
  water will likely inundate pasture land, some campgrounds, cover
  hiking and biking trails, as well as roads leading into the
  high country.


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

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



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