Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 200434 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
934 PM PDT Sat Aug 19 2017

.UPDATE...
Another active evening is winding down with the loss of daytime
heating. Cloud tops were warming and radar signatures continuing
to decrease with only a low risk of additional lightning strikes
this evening north of Pyramid Lake. Cells today were once again
slow moving and outflow dominated with renewed initiation along
these rather deep outflow boundaries which helped keep the storms
going well into the evening. Locally heavy rain and wind gusts to
50 mph were observed with very little hail. Isolated storms are
again expected Sunday although coverage may be a bit less and more
focused along and west of the Sierra Crest. Storms will remain
slow moving so locally heavy rain will still be possible with any
storms that do develop. Hohmann

&&

.SYNOPSIS...

Thunderstorms remain possible each day through the middle of next
week. Storms Sunday will again develop over the Sierra, but we
will see increasing coverage across the Pine Nut and Virginia
ranges in western Nevada. Flash flooding will become more of a
threat into early next week. Temperatures through the weekend will
remain above average with weak afternoon breezes each afternoon.

&&

.PREVIOUS DISCUSSION... /Issued 1250 PM PDT Sat Aug 19 2017/

SYNOPSIS...

Thunderstorms remain possible each day through the middle of next
week. Storms this evening and Sunday will again develop over the
Sierra, but we will see increasing coverage across the Pine Nut
and Virginia ranges in western Nevada. Flash flooding will become
more of a threat into early next week. Temperatures through the
weekend will remain above average with weak afternoon breezes each
afternoon.

SHORT TERM...

Low pressure remains off the Southern/Central CA Coast through the
weekend, keeping moisture and instability over the Sierra and
western Nevada. Isolated to scattered showers and thunderstorms
are already developing over the Eastern Sierra and Tahoe Basin
this afternoon. Storm coverage will continue to increase through
this evening, with zephyr west winds kicking in and increasing
low- level convergence over the western Nevada Sierra Front after
5pm.

Storms today and Sunday will be very slow moving, as there is very
weak steering flow in the mid-levels. These storms will be
capable of producing localized heavy rainfall with potential for
flash flooding in favored areas such as steep terrain and recent
wildfire burn areas. Yesterday evening we had a storm that
developed right over the Farad Fire burn scar and produced debris
flow over I-80 that closed the interstate for a time. An
additional heavy rainfall on the burned area could produce more of
the same over the next few days.

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 as well. These converging
outflows will also help to trigger additional thunderstorm
developing east of Highway 395 this evening. Anyone with outdoor
plans this weekend should prepare for the potential for afternoon
and evening thunderstorms and have a plan "B" in case a
thunderstorm develops over your area.

An uptick in easterly flow is expected on Sunday. This will
likely keep thunderstorm development mainly over the High
Sierra/Tahoe Basin and pushing west of the crest, so the feeling
is that today will be the best chance of thunderstorms over
western Nevada with better convergence and a weak zephyr late this
afternoon.

Smoke and haze will continue to affect the region over the next
few days as wildfires continue to burn in CA/OR/ID/MT. This smoke
and haze that we are seeing today is not from one fire in
particular, but just a glob of smoke that is hanging over the
Western States from the combined active wildfires across the
region. See our earlier post from this morning on social media
with the visible satellite image from GOES-16.

On Eclipse Monday, we may have a few clouds hanging around in the
morning, especially from Sunday night thunderstorms over Southern
Nevada potentially bringing up mid and high clouds for Monday
morning. We will continue with a partly cloudy forecast for Monday
morning, with potential for some smokey haze from ongoing western
wildfires. Thunderstorm activity is expected once again on Monday
afternoon. A vortmax coming around the low will move through
Central Nevada Monday, helping to get some thunderstorm activity
going for areas east of Fallon/Hawthorne. Hopefully the clouds
will hold off until after the eclipse, but overall the forecast
confidence is still low regarding the details when it comes to
these cut-off lows. Hoon

LONG TERM...Tuesday through Saturday...

No significant changes to the long term forecast. Pesky upper low
near the southern California coast will finally shear out or weaken
to near non-existence by Wednesday night and Thursday as a trough
moves into the Pacific Northwest. This is expected to lead to drier
and more stable flow late next week with diminishing chances for
thunderstorms.

Tuesday and Wednesday, isolated to scattered mainly afternoon and
evening thunderstorms are expected. Tuesday currently looks to offer
the better upper forcing with the more intact upper low bringing
upper divergence to the region. Moisture will be elevated with PWATs
between 0.75" and 1" and storm motions modest (especially Wednesday);
therefore, localized heavy rain is likely with locations susceptible
to flash flooding (burn scars/terrain stripped of vegetation, steep
terrain) seeing an increased risk for impacts.

Thursday, afternoon winds could increase some as drier southwest
flow pushes into the region. Friday and Saturday, an upper ridge is
simulated by the GFS/EC to build back overhead for warming
temperatures and minimal chance for thunderstorms. -Snyder

AVIATION...

Greatest threat for aviators will be scattered showers and
thunderstorms this evening, mainly along the Sierra and western
Nevada Sierra front. Storms are likely to form after 21z today,
dissipating 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: 20 percent, 21z-03z
KTRK and KTVL: 25 percent, 21z-01z
KMMH: 30 percent, 21z-03z
KLOL and KNFL: 20 percent, 00z-05z

Thunderstorm chances continue through the weekend and then
increase as we go into the first half of next week.

Otherwise, expect VFR conditions over the weekend with afternoon
westerly breezes of 8-12 kts. If it rains at KTRK, the airfield is
likely to see fog develop overnight into the early morning hours.
-Dawn/Hoon

&&

.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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