Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 201014

Area Forecast Discussion
National Weather Service Reno NV
314 AM PDT Sun Aug 20 2017


Showers and thunderstorms will be possible mainly across the Sierra
through Monday with increasing coverage expected for Tuesdays.
Isolated flash flooding and gusty outflow winds are expected through
Monday, but an enhanced potential for flash flooding is expected by
Tuesday afternoon. Temperatures will remain a bit above season
averages through the week with light afternoon breezes each



A slow moving cut-off low off of the southern California coast will
provide a persistent pattern of afternoon Sierra showers and
thunderstorms through Monday with increased potential and coverage
expected on Tuesday. Storm formation will be favored along the
Sierra, particularly across northern Mono county through the southern
Tahoe Basin. Easterly steering flow should keep cells confined to
the Sierra and west slopes particularly on Monday when the flow
increases to 20-25 knots roughly south of Hwy 50.

These storms will be capable of producing localized heavy rainfall
with a potential for localized flash flooding in favored areas such
as steep terrain and recent wildfire burn areas. Thunderstorms will
also be capable of producing small pea size hail and frequent cloud
to ground lightning. The inverted-V soundings and dry boundary layer
will have potential for strong gusty outflow winds up to 50 mph.

Tuesday looks to be the most favorable day for storms due to flow
becoming lighter and shifting southerly. This will help transport
deep layer moisture through the area and also position divergent
flow aloft across northern Nevada. This deeper moisture, slower
storm motions, and forcing could help develop lines of training
storms which will provide an elevated risk for flash flooding across
the region. Those with outdoor plans should closely monitor the
forecast and consider alternate plans.

Also, closely watching the potential for smoke, haze, and clouds for
the eclipse viewing on Monday morning. Most of the smoke and haze is
originating from fires through California and Oregon, so the good
news here is that as the low nears the coast, we expect easterly
flow to strengthen through Monday which would aid in keeping the
smoke away from our region. Cloud cover on the other hand may be a
bit more problematic, particularly for areas such as southern Mono
and Mineral counties. Moisture will begin to surge northward on
Monday, but the bulk of the mid and high level clouds is looking to
remain roughly south of Highway 50 through the morning and then
increase northward through the afternoon. Overall partly cloudy
conditions will remain in the forecast, with better chances for less
clouds north of Highway 50 through to the Oregon border where
wildfire smoke may be more of the issue there. Fuentes

.LONG TERM...Wednesday and beyond...

The low off the southern California coast begins to weaken and shift
inland on Wednesday in response to a stronger area of low pressure
moving through the Pacific Northwest. This will provide steepening
upper level lapse rates, with a secondary vort max rotating through
the flow aiding in thunderstorm development on Wednesday. Deep
moisture remains across the region on Wednesday with PWATs in the
0.8-1.0" range. Steering flow is light, but will strengthen slightly
going into the evening hours, turning from the southeast to south
southwest. Despite the increase, flow is light enough to keep the
concern for flash flooding especially over steep terrain or recent
burn scars. Soundings would also suggest the potential for strong
and gusty outflow winds. The one caveat is that if we end up with
extensive cloud cover Wednesday morning from the convective debris
Tuesday and Tuesday night, which is possible given the situation, we
may not realize the full instability potential.

Behind the low, drier westerly flow returns to the region with
increased afternoon breezes. There may be enough lingering moisture
and instability across north central Nevada eastward for a stray
thunderstorms to form Thursday. By Friday and into the weekend,
storm chances look minimal if not non-existent as most ensemble
members are indicating a large ridge building across the west. This
is likely to bring high temperatures 5-8 degrees above normal by the
weekend. -Dawn



Scattered showers and thunderstorms are most likely over the Sierra
after 21z with isolated storms across western Nevada, mainly near
and south of I-80 after 22z. The easterly flow will help storms that
do develop slowly drift westward, however outflow boundaries can
cause storms to deviate from the overall flow. Storms will dissipate
between 03-05z.

Brief periods of heavy rain, gusty and erratic outflow winds can be
expected with lesser chances for a hail threat. Localized terrain
obscuration is a concern along with short periods of MVFR-IFR
conditions under the rain core of the storms.

Chances and most likely timing for a thunderstorm to impact or be in
the vicinity of a terminal site:

KRNO and KCXP: 15 percent, 22z-04z
KTRK and KTVL: 25 percent, 21z-04z
KMMH and KBAN: 35 percent, 21z-04z
KNFL and KLOL: 15 percent, 23z-04z

Thunderstorm chances and coverage will increase the first half of
the week.

Otherwise, expect VFR conditions with afternoon westerly breezes of
8-12 kts. Early morning patchy fog remains possible around KTRK if
the airfield receives rainfall. Fog started to form early this
morning at KTRK, but increasing clouds helped to limit development.


.REV Watches/Warnings/Advisories...


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