Area Forecast Discussion
Issued by NWS Reno, NV

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205
FXUS65 KREV 222239 AAA
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
310 PM PDT Thu Jun 22 2017

UPDATED TO ADD HYDROLOGY SECTION

.SYNOPSIS...

High pressure will bring much above average temperatures through the
weekend, with between 5 and 10 degrees of cooling possible next week.
Isolated thunderstorms are possible through Saturday near the Sierra,
spreading into parts of western Nevada Sunday. Dry and breezy
conditions are expected early next week. Flooding will continue for
the creeks in Mono County and for portions of the Walker River.

&&

.SHORT TERM...

The main forecast changes were on Sunday, with an increase in the
chance for thunderstorms north of Susanville and Gerlach, as well
as increased winds for much of western NV and the Mono County Sierra
Front.

As expected so far this afternoon, cumulus development has been limited
to Mono County over the higher terrain. The cumulus are deepest well
west of the crest where the best low level convergence exists (likely
due to the thermal gradient near the snow line), with only shallow
convective development in Mono County. Going into this evening, there
is a good chance that any/all deep convection (thunderstorms) will
remain on the west side of the crest near the snow line. However,
there is a low probability that a very isolated cell could develop
on the eastern flanks of the Sierra before dark so a slight chance
was left in the forecast.

For Friday and Saturday, a ridge axis settles over the Sierra and
western Nevada with temperatures in the lower valley rising to around
the century mark once again by Saturday. Mid-level temperatures do
not change much through Saturday so a few afternoon and evening
storms cannot be ruled out in the Sierra south of Highway 50.

Sunday is expected to bring the hottest day for most areas, as
well as an increase in thunderstorm coverage as a modest upper
disturbance moves over northern California and western Nevada. The
disturbance will enhance the chance for afternoon and evening
thunderstorms as temperatures aloft cool (instability) slightly
and a zephyr (focus) develops as cooler air invading the Central
Valley enhances thermal gradients across the region. One caveat
for storm coverage will be the timing of the wave. Current NAM,
GFS, and EC simulations push the wave forcing through the Reno-
Tahoe area by late morning. If this occurs, coverage could be more
isolated south of I-80 with the best focus over northeast CA and
far northwest NV (north of Susanville and Gerlach) ahead of the
wave. With some uncertainty, POP could not be changed too much
although a slight bump was given to northern areas with better
disturbance timing per recent simulations. -Snyder

&&

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

Next week brings the promise of dry, breezy conditions and a
gradual cool down early to mid-week as an upper disturbance moves
into the Northwest CONUS. This will become a fire weather issue,
especially if fires start from Sunday`s thunderstorm activity. See
the fire discussion for more details. For the mid to latter
portion of next week, model discrepancies develop as the EC
builds a ridge back overhead Wednesday and Thursday while the GFS
keeps flat or northwest flow aloft with stronger energy over the
Northwest CONUS. -Snyder

&&

.AVIATION...

A very isolated thunderstorm is possible this evening south of
Mono Lake...a 5-10% chance. We have left it out of the KMMH TAF,
but any trans-Sierra flights should be aware of potential late
day thunderstorms over the Sierra south of Alpine County today
and Friday.

Otherwise, VFR conditions expected through the Friday with light
northeast to east flow. Thunderstorm chances return for the
weekend as temperatures increase to well above normal. Snyder/Hoon

&&

.FIRE WEATHER...

Well above average temperatures and afternoon thunderstorms will
continue through the weekend. Critical fire weather conditions are
probable next Monday and/or Tuesday as a low pressure system
approaches the west coast causing an increase in winds.

Thunderstorms will mostly be confined to the high terrain of the
eastern Sierra today and tomorrow and potentially spread into the
Tahoe Basin on Saturday. Sunday will be the day to watch for
thunderstorms as chances increase throughout the region. High storm
bases and storm motions around 20kts will increase the chances of
lightning strikes outside of rain cores. Very dry low levels will
could also create the potential for erratic winds gusts in excess of
50 mph.

A trough approaching the west coast will drawn in very dry air along
with an increase in winds starting Monday. Critical fire weather
conditions will be possible Monday and Tuesday, potentially
lasting into midweek. -Zach

&&

.HYDROLOGY...

Rapid snowmelt from the remaining deep high elevation snowpackwill
bedrivenbyhot days and warm nights.Expect continuedvery high
flows at least throughSundaynight on creeks and streams draining
high elevation terrain near the Sierra Crest as well as creeks
draining the eastern and northeastern flanks of Mt. Rose. This
includes the forks of the Walker River, other creeks and streams in
Mono County, Galena Creek, and neighboring creeks in the Mt. Rose
area.

Peak nighttime flows throughSundaynight are likely to be similar
to observed peaks over the last three nights. A combination of
slightly cooling temperatures and depleting snow covered
contributing area should lead to gradually decreasing flows starting
early next week.

Preliminary measurements of snowmelt flows on the West Walker above
and below Topaz reservoir have exceeded the previous snowmelt peak
flow of 1995 and that water is slowly moving into and through the
Mason Valley. Fortunately this year at this time, the East Walker
is contributing significantly less water than it was during the peak
of 1995. The combination should lead to flows and impacts in the
Mason Valley and downstream similar to or slightly less than from
the peak flows of mid-July 1995.

&&

.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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