Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 190949

Area Forecast Discussion
National Weather Service Reno NV
249 AM PDT Fri May 19 2017


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. Significant flooding is
possible along the Walker River in Mason Valley. Some flooding is
also likely for the upper portions of the Carson and Truckee
River systems.



Temperatures trend much warmer over the next few days as the east
Pacific ridge shifts into the Western United States. Expect the
rate of snow melt to increase as a result leading to flood issues
along creeks and streams out of the Sierra as well as main stem
rivers in western Nevada. Locations along the Walker River will be
the most susceptible to flooding especially along the Mason
Valley near Yerington. Effects are expected to be most similar to
the flooding that occurred in the Spring of 2011; moderate
flooding of lowlands, pasture, and farmland adjacent to the river
throughout Mason Valley with some rural and secondary roads also
becoming flooded. Expect basements of the lowest elevation homes
in Mason Valley to begin to flood. These impacts are expected to
begin Sunday and are likely to extend into June. Now is the time
to prepare by moving property to higher ground. For the Truckee
and Carson River systems, expect flows to increase markedly. Some
minor flooding right along the rivers is possible, but there are
more water management controls for these rivers.

Otherwise, forecast parameters are relatively benign. There is the
chance for isolated thunderstorms beginning Sunday afternoon
mainly from Alpine County southward in the Sierra. The chances of
thunderstorms for Lassen/Plumas Counties were removed based on
expected trough position and unfavorable northeasterly wind flow.
There could still be a few build-ups, but only amount to about a
10% chance of rain showers north of the Tahoe Basin. Also,
thunderstorm chances were pinned to the Sierra crest west of
Highway 89 in the Tahoe Basin. Boyd

.LONG TERM...Monday through Thursday...

Above average temperatures and mountain snowpack melting will
continue next week and flooding is forecast for some areas along
mainstem rivers. Creek and small stream flooding is also expected
for some areas. For further discussion of these dangerous hazards
and their impacts, see the hydrologic warning and advisories at

The flow will be relatively light as high pressure dominates over
the intermountain west with weak low pressure off the California
coast. This will result in very warm temperatures and based on
latest guidance, temperatures will easily push into the mid-upper
80s across western NV as early as Monday with some lower 90s
Tuesday through Thursday. Based on forecast 700 MB temperatures
near 10C and a well mixed boundary layer, high temperatures at
Reno will be very close to 90 degrees. We raised temperatures
based on this pattern and the fact we are getting into late May.

Another impact from this pattern will be a gradual increase in
instability with some moisture transport between upper high and
low along the eastern Sierra. Isolated thunderstorms will be
possible mainly south of Lake Tahoe for Monday before spreading
northward along the crest into western Lassen County Tue-Wed as
southeast flow becomes more pronounced. 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 would have a
better push east off the Sierra into western NV Thursday with
drier conditions and less storm potential Friday into the weekend.
Confidence in the details is low however. Hohmann



VFR conditions through the rest of the week, with light winds and
mostly clear skies. Expect afternoon cumulus buildups and a chance
for thunderstorms over the Sierra starting Sunday. JCM


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

CA...Flood Watch from Sunday morning through Tuesday evening



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