Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 181011
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
311 AM PDT Thu May 18 2017

.SYNOPSIS...

A warming trend will start today, with above average temperatures
by Saturday. The above average temperatures this weekend will
accelerate snowmelt in the Sierra. River and stream flows will
increase with an enhanced risk for river flooding, especially on
the Walker River, and possibly the Carson River, by next week. A
few thunderstorms may form near the Sierra starting on Sunday.

&&

.SHORT TERM...

High pressure builds over the West Coast today beginning a
significant warming trend. Light easterly flow will keep high
temperatures somewhat tamped down today, upper 60s to around 70
for western Nevada and upper 50s to around 60 for Sierra valleys,
before the pressure gradient weakens further into the weekend.
Afternoon highs increase into the low 80s for western Nevada and
low/mid 70s for Sierra valleys by Sunday.

River Rises: While weather parameters are generally benign,
snowmelt will increase resulting in additional runoff into area
rivers. The bottom line is that all rivers will be running fast
and very cold; stay away from the rivers if possible. See our
hydrology section below for more flooding details. Boyd

.LONG TERM...Sunday through Wednesday...

Ridge of high pressure continues to amplify on Sunday along the
Pacific Northwest coast, while a weak shortwave trough dropping
through the northern Rockies splits off over CA. The ridge will
keep temperatures warm, around 5-10 degrees above average. The
weak low pressure dropping over CA will bring a few degrees of
cooling aloft that will help to increase instability over the
Sierra. This will bring chances of thunderstorms for the Sierra
Sunday through Wednesday, mainly driven by afternoon heating and
terrain convergence over the High Sierra.

Temperatures will continue to rise into next week as high pressure
dominates. Highs will reach into the mid 80s by next week in
western Nevada and mid 70s in the Sierra. Snowmelt will increase
with the well above normal temperatures. Rises are expected for
creeks, streams, and mainstem rivers coming out of the Sierra
through next week. See our hydrology section below for more
details of potential snowmelt flooding. Hoon

&&

.AVIATION...

VFR conditions through the rest of the week, with light winds and
mostly clear skies. Hoon

&&

.HYDROLOGY...

Warming temperatures late this week and into the weekend will
accelerate snowmelt in the Sierra. Overnight low temperatures in
the higher elevations are likely to remain above freezing as well...
and this will enhance snowmelt further.

This increased snowmelt will cause 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 at the very least.
Farther downstream...flooding possibilities will increase for some
of the major basins. Minor flooding is possible by the middle of
next week for the Carson Valley area while moderate flooding is
highly likely for the Walker River system from Antelope Valley
downstream into the Mason Valley...with more extensive flooding
possible in Mason Valley. Higher flows are also likely below Weber
Reservoir...but the expected extent is unknown at this time.

Currently the extent of any flooding is uncertain. Some factors that
are unknown at this time include how high temperatures will reach
and for what period of time, as well as how reservoir operations
will change to mitigate flooding concerns. The Walker River is the
biggest concern at this point in time...but not the only area of
concern.

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...None.
CA...None.
&&

$$

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



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