Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 231044 CCA

Area Forecast Discussion
National Weather Service Reno NV
337 AM PDT Tue May 23 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 minor flood stage Wednesday then cresting just below
moderate flood on Friday. Some minor flooding is also likely for
the upper portions of the Carson and Truckee River systems. Gusty
winds can be expected Wednesday into Thursday with cooler
conditions for the end of the week.



Significant changes were made yesterday to the flood outlook for
the Walker River; overall less flooding is expected. Please, read
the Hydrology section below for details.

Winds were generally increased for Wednesday and Thursday as a
cold front dips into the region. Expect breezy to gusty winds
along the Sierra Front into the Basin and Range. Gusts will be in
the 30 to 40 mph range while wind prone locations could see gusts
as high as 50 mph. Boating activities will become hazardous for
area lakes beginning Wednesday afternoon; plan accordingly.

With a cold front moving into the region by mid week, today will
be the warmest day with western Nevada temperatures around 90
degrees and Sierra valleys in the mid/upper 70s. Expect
temperatures to drop to around 80 degrees by Thursday in western
Nevada and into the upper 60s for Sierra Valleys. Some Sierra
valleys will dip into the low 30s over Thursday night.

Thunderstorms are still forecast today along the Sierra crest in
Mono County as surface instability and convergence drive forcing
for ascent. These will be garden variety and very isolated. More
dynamic forcing will be present Wednesday as a trough moves
towards the region. Expect isolated thunderstorms for Mono/Mineral
Counties, along the Lassen convergence zone, and areas north of
Gerlach. Boyd

.LONG TERM...Friday through Monday...

No significant changes were made as large scale pattern features a
trough on Friday followed by a ridge for the weekend into Monday.
Moisture and instability with the trough will be north and east of
the region so it will likely stay dry. Temperatures will be closer
to normal Friday after a cold start with some colder Sierra valleys
dropping to freezing. Saturday morning will once again start cold
for valley locations as upper slopes and ridges begin to warm under
building ridge. Temperatures will then stay well above normal from
Saturday afternoon through Monday with highs well into the 70s
Sierra valleys and mid 80s to around 90 lower valleys. This will
once again accelerate flows on creeks and streams flowing out of the
Sierra after a slight lull Friday-Saturday.

There are indications that instability will gradually build along
the Sierra as light southeast to south flow develops between ridge
and east Pacific trough for the middle of next week. Thunderstorm
potential may go up Tuesday and Wednesday although there are still
some drier scenarios. Hohmann



VFR conditions with light winds today. A slight increase in
instability today will allow for cumulus development and possibly
one or two thunderstorms right along the Sierra crest of Mono
County. As a trough drops down on Wednesday, there is a slightly
better chance across Mono-Mineral Counties although coverage will
remain isolated. There may also be a shower or thunderstorm along
front north of I-80. West flow will pick up Wednesday ahead of front
with ridge wind gusts increasing to 50 kts and surface gusts
generally 30-35 kts. Some turbulence is possible along the lee of
the Sierra. Hohmann



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 minor/moderate 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.


* Walker River forecast has been lowered to minor/moderate
  flooding. Major flooding is no longer expected. Current
  projections have a peak flow just below moderate levels, near
  10.8 feet or near 2500 CFS. Minor flood stage will be reached
  Wednesday morning and flow will peak out late Friday.

* There are several reasons for the updated forecast: less
  response form the snowmelt over the last couple days, new
  emergency gages that have been installed near Topaz allowing for
  more precise management and forecasting of the West Walker
  River, change in anticipated releases from Bridgeport Reservoir,
  and slightly cooler temperatures expected for the weekend.

* Minor flooding is possible on the East and West forks of the
  Walker River. Minor flooding is already occurring on the West
  Walker River just downstream of Wilson Canyon. Areas potentially
  affected include Antelope and Smith valleys. Higher flows are
  also eventually 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

* 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 and roads leading into the high country.


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

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



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