Special Weather Statement, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
1221 PM PDT Sun Aug 6 2017

.SYNOPSIS...

Low pressure stalled over northern California will produce
thunderstorms with heavy rainfall possible through midweek. A few
storms could become severe and produce flash flooding this
afternoon and evening. Drier weather returns late in the week.
Temperatures will remain slightly below average through Wednesday,
followed by some warming.

&&

.SHORT TERM...

Upper area of low pressure remains nearly stationary over northern
California, keeping a steady stream of moisture into the Sierra and
northwest Nevada. With clear skies to start the morning, outside of
central NV eastward, it helped to destabilize the atmosphere
further. The 12z and 18z KRNO soundings showed a cap around 500 mb,
which may hold off initial convection until early afternoon, but
will also allow storms to get going faster once it breaks. The HRRR
agrees with this idea with rapid storm development after about 20z,
or 1 pm local time.

When modifying the KRNO sounding, was able to get 500-1000 J/kg of
CAPE and -4 LI, which lines up with forecast model soundings as
well. Forecast soundings are also indicating increasing PWATs
through the day, pushing toward nearly 1" by late afternoon. This
value, climatologically, is indicative of increased flash flood
risk, especially given the fact that storm motions overall will be
less than 10-15 kts. A Flash Flood Watch remains in effect through
this evening for much of northeast California and northwest Nevada,
with a heightened risk for recent burn scars and steep terrain. The
Tahoe Basin and eastern Sierra was kept out of the watch due to the
westerly zephyr afternoon winds helping to push any storms that do
develop eastward. The greatest storm risk today will be locally
heavy rainfall. Gusty outflow winds in excess of 50 mph, small
hail, and frequent lightning area all risks as well. Today may
bring a mix of severe storms and flash flooding based on the
current forecast parameters. Showers and isolated thunderstorms
are likely to continue into the overnight hours as well.

PWATs remain high, just over 1" according to KRNO forecast
soundings, through midweek with the upper low remaining over north
central California. The big question at this time is the amount of
lingering cloud cover. Frequently, we can become clouded over once
the atmosphere becomes that moist, which then ends up limiting
thunderstorm coverage; this was what happened Saturday. Forecast
models and sounding are indicating increasing amounts of CAPE
through Wednesday, however extensive cloud cover could keep this
from being fully realized. Will maintain scattered thunderstorm
coverage in the forecast Monday-Wednesday at this time with
locally heavy rainfall likely to be the greatest threat. -Dawn

.LONG TERM...

Upper low begins to shift eastward by the end of the week with some
increase in southwest flow. This will finally start to bring a
drying trend to the region, however there will be enough lingering
moisture and instability for a few storms to form Thursday and Friday
afternoons, especially near favorable convergence zones. A warming
trend is also on tap for the end of the week going into the weekend,
with high temperatures about 5 degrees above normal.

An upper low moves into the Pacific Northwest coast for the start of
next week which is likely to increase southwest to west winds across
the eastern Sierra and northwest Nevada. The current forecast
position of the low should keep a dry and stable airmass over the
region and thunderstorms are not anticipated. -Dawn

&&

.AVIATION...

Fairly widespread showers and thunderstorms are expected this
afternoon and evening bringing locally heavy rainfall, gusty and
erratic outflow winds of 40 kts or greater, small hail, and frequent
lightning. Storms are expected to form between 19-21z and continue
through approximately 04-06z this evening. A few showers with
isolated thunderstorms may continue through the night. Storms may
obscure terrain and bring localized MVFR-IFR conditions.

Chances for a thunderstorm to pass over a terminal and best timing
for each location today (Sunday) are:

KRNO and KCXP: 60% 20z-01z

KTVL and KTRK: 40% 20z-23z

KMMH: 50% 19z-00z

KLOL and KNFL: 60% 21z-04z

Ongoing wildfires continue to bring hazy conditions to the region,
but the overall flow and recent precipitation has helped to
improve visibility today compared to Saturday. -Dawn

&&

.REV Watches/Warnings/Advisories...
NV...Flash Flood Watch until 10 PM PDT this evening NVZ001-003>005.

CA...Flash Flood Watch until 10 PM PDT this evening CAZ070-071.

&&

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

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Special Weather Statement
National Weather Service Reno NV
1237 PM PDT SUN AUG 6 2017

NVZ001-062000-
Mineral and Southern Lyon Counties NV-
1237 PM PDT SUN AUG 6 2017

...Strong thunderstorm near Sweetwater Summit...

At 1235 PM PDT, Doppler radar was tracking a strong thunderstorm 12
miles east of Walker, or 14 miles east of Coleville, moving north at
10 mph.

Small hail, heavy rain, and winds in excess of 40 mph will be
possible with this storm.

Locations impacted include...
Sweetwater Summit, Junction Nv 338 And Nv 829 (wellington Cutoff),
Pine Grove and Smith Valley.

LAT...LON 3844 11918 3854 11932 3875 11933 3873 11904
      3851 11909
TIME...MOT...LOC 1935Z 181DEG 11KT 3853 11925

MB