Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 172154

Area Forecast Discussion
National Weather Service Reno NV
254 PM PDT Sat Jun 17 2017

High pressure will bring much above average temperatures into
next week with records possible Monday through Wednesday. The
threat for thunderstorms will increase into Monday and Tuesday.
Isolated storms are possible in the Sierra this weekend with
storms spreading north to the Oregon Border and Western Nevada by
Monday. Snowmelt runoff will increase flows especially in the
Walker River basin and creeks in Mono County.


A few changes have been made, mainly to increase the thunderstorm
chances early in the week and slow the cooling trend at the end of
the week. The main story continues to be the heat with record
highs possible Monday through Wednesday from strong high pressure
centered over Arizona.

This afternoon, some cumulus are developing, with the thunderstorm
threat again looking to be low. Still, kept in a slight chance of
storms, but moved them off the crest closer to the US-395
corridor. Anything that develops early this evening will likely be
on the warm side of the snowpack edge. Also, tonight winds will
become a little more northeast and gusty on the ridges with gusts
up to 40 mph likely.

Sunday, temperatures remain warm and instability increases a bit
over the Eastern Sierra with storms a little more likely. However,
they are likely to remain there and not spread into Western NV
except perhaps the Sweetwaters, due to light NE flow aloft.

Things get more interesting Monday as the ridge builds stronger
into NV with near record temps. This will aid instability with
higher than normal precipitable water and dewpoints continuing.
While there is no feature in the mid to upper levels of the
atmosphere to trigger convection, subtle changes will increase
low-level forcing. The upper flow becomes more south which could
trigger a late afternoon zephyr. We have greatly expanded the
thunderstorm coverage Monday to most of NE California and Western
NV, the exception being the Humboldt and Carson Sinks.

Tuesday the flow becomes more southwest with thunderstorms slowly
decreasing, but there should still be enough moisture for isolated
storms most areas. Temperatures will remain hot with records
possible again. Note that the thunderstorms bring fire weather
concerns and these are addressed more below.

For Wednesday through Saturday, the GFS/EC diverge, but the
overall trend in the models and ensembles is warmer with a light
southwest flow. Wednesday will see near record highs again with
slightly cooler temps late in the week. The GFS shows windy
conditions Friday while the EC has the ridge rebuilding. The GFS
is quite a bit cooler with temps close to average by Saturday
while the EC keeps near record temps into next weekend. We will
continue a middle of the road approach with dry conditions and a
very slow cooldown. Wallmann


VFR conditions into Sunday with only isolated thunderstorms
possible in Mono County 00-03Z this evening and again 22-04Z
Sunday afternoon/evening. Winds will be light aside from gusty NE
ridge winds tonight with light mtn wave turbulence.

Better chances for thunderstorms which may affect terminals Monday
and to a lesser extent Tuesday. Density altitude will be quite
high for KRNO which may impact operations. Wallmann


The very warm temperatures will continue to dry out grassy and
finer brush fuels during the next several days across western NV.
By Monday, potential for thunderstorms increases near the Sierra,
and across portions of western NV mainly from the Sierra Front
southward to western Mineral County. Projected surface dew points
in the 40s with PW values at least 0.80 inch and slow movement will
favor wet thunderstorms. A few lightning-induced fire starts are
possible, but with this amount of moisture the fuels will be less
receptive to ignition, and rain associated with these storms will
have a good chance of ending any fires that might start. Therefore
we are not planning any watches or warnings, but will headline
the thunderstorm threat in the afternoon Fire Weather Forecast.



Persistent heat and mild overnight temperatures will lead to
progressively higher snowmelt rates in the remaining deep, high-
elevation snowpack. In many basins, these higher melt rates will
have limited impacts due to the relatively small remaining snow
covered area. In contrast, areas draining from high elevation
terrain near the Sierra Crest generally do have adequate remaining
deep snowpack to sustain high flows for area rivers.

The areas of highest concern are the Walker River system and
other creeks and streams draining from the Eastern Sierra into
Mono County. Flows are expected to increase daily with peak flows
occurring overnight or in the early morning hours from the middle
to the end of next week. These flows are expected to match, or
exceed, previous high flows that occurred earlier this season.
High flows are likely mid to late next week farther downstream on
the Walker River in Mason Valley and beyond, but the magnitude is
highly uncertain due to reservoir management decisions and the
timing of area reservoirs reaching their capacities. While
impactful flooding is not expected on the Tahoe Basin creeks or
the forks of the Carson River, very high flows are expected which
could cause minor issues and could be a risk to people recreating
in the mountains. Bardsley


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