Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 282120
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
220 PM PDT THU JUL 28 2016

.SYNOPSIS...

Hot and dry conditions will prevail this week with a few record
highs possible. A slow increase in moisture will lead to a few
afternoon and evening thunderstorms, especially Friday. High
temperatures will ease downward early next week as a trough moves
through the Pacific Northwest.

&&

.SHORT TERM...

Temperatures continue to climb toward record levels this afternoon
with most stations up a couple of degrees in the past 24 hours as
of early this afternoon. Latest model data shows little change
for Friday as 700MB temps push 18-19C and only a gradual "cooling"
will occur this weekend as a trough passes through the Pacific
Northwest and helps to nudge/weaken upper ridge. The heat advisory
will remain in place through Friday with conditions getting near
advisory levels along the Sierra Front. Make sure to take
precautions during this hot weather to reduce the risk of heat
stroke or heat exhaustion. Never leave children or pets in your
vehicle, even for a few minutes!

On the flip side, we do have a risk of thunderstorms through the
weekend as moisture continues to seep into the eastern Sierra
underneath upper ridge. The 12Z sounding at KREV showed PWAT
values close to 0.75" and given the intense heat, any convergence
off local terrain will be capable of producing updrafts strong
enough to result in buildups and thunderstorms. Storms this
evening will be confined mainly from Alpine County/Pine Nuts
southward, then spread north to the Oregon border Friday with a
bit more coverage from the Virginia Range and Pine Nuts southward
as the leeside zephyr becomes a bit better developed.

There is very little steering flow today and instability is a bit
marginal, so storms will be slow moving and not well organized
(pulse storms). A slight increase in storm flow should help storms
move off the Sierra and into western NV on Friday with movements
slightly faster and storms a little more organized/stronger.
Storms may still anchor in favored locations along the terrain
and be capable of locally heavy rain. However, the primary threat
continues to be strong outflow winds due to the very hot and dry
sublayer. Gusts over 50 mph are likely with 60+ mph possible with
any storms that drift out over the hotter valleys. These outflows
will be capable of traveling well away from storm cores and may
pick up dust in the Hwy 95 corridor. Thunderstorm coverage will be
more isolated over the weekend and mainly south of Hwy 50 as drier
air works into northern areas on increasing west flow. Hohmann

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

Next week looks to be a relatively quiet weather pattern as
shortwave energy moving across the Pacific Northwest early next week
displaces the ridge axis back to the southwest and south central
states. This will keep the extreme heat out of our region, but
daytime highs will remain a few degrees above average, mainly in the
mid 90s to near 100 degrees for lower elevations and 80s near the
Sierra.

For Monday-Tuesday, the shortwave passages are likely to kick up the
winds each afternoon, with potential for gusts near 35 mph. This
could lead to fire weather concerns, especially if any new fires
from this week`s thunderstorm activity are actively burning. Lighter
breezes are then expected for Wednesday-Thursday.

As for thunderstorm chances, this looks slim as dry and more stable
pattern prevails next week. The only possible exception may be in
far southern Mono-Mineral Counties on Monday, where lingering
moisture and weak convergent flow could kick off a few cells late in
the day. MJD

&&

.FIRE WEATHER...

Isolated thunderstorms are expected late this afternoon and evening
in Mono and Western Mineral Counties with a storm or two possible in
the Pine Nuts and just north of Truckee as well. Moisture has
increased, but instability still isn`t great. That said, more
cumulus have already formed with a few buildups already noted
south of Markleeville and onto the Mono County crest. These will
be slow moving with some rain, but cores will be small so a few
dry strikes are likely.

Tomorrow still looks good for at least isolated convection along the
395 corridor. More of a zephyr is expected Friday which will
enhance convergence. In addition, moisture will increase a little
more and combine with the convergence for more storms. This is not
a classic dry thunderstorm pattern, but with fuels very dry and
coverage 15-30% there could be issues as ignition efficiency may
be high. Also, the storms will have a little more motion to them
so rainfall from the storms will be light to moderate at best.

Upgraded the Sierra Front south to a warning where coverage will be
greatest, but further north is a bit more of a question. I am not
sure we will get the coverage there to warrant a warning, but there
will be a couple storms at least. So far, while there are a few
clouds over Plumas/Sierra Counties, they remain flat. If they look
better or do develop a storm, confidence will grow about the north
for Friday.

Saturday, southwest winds increase with thunderstorms mainly
confined to Mono/Mineral Counties. This trend to continue into
Sunday with locally breezy zephyr winds to the north.

&&

.AVIATION...

Isolated afternoon thunderstorms (mainly before 04Z) and hot
temperatures will be the main weather impacts for aviation through
Saturday. Today, the threat of thunder will primarily extend from
Mono County northward to the Pine Nut mtns in eastern Douglas
County (including KMMH). By Friday, the chance for thunder spreads
northward across KMEV-KCXP-KRNO-KSVE. By Saturday the best chance
for thunder shifts east to include KNFL-KHTH-KMMH and possibly
KLOL.

Cells will be slow moving, especially today and Friday, but high-
based such that outflow wind gusts of 40+ kt and lightning will
be the primary hazards, with brief periods of MVFR in rain
showers. Some increase in cell motion is likely Saturday, with a
greater potential for blowing dust reducing visibility in west
central NV downwind from the sinks and dry lake beds.

Other than gusty thunderstorm outflows, winds will be rather light
through Friday with only weak late day zephyr breezes producing
gusts 20 kt or less. By Saturday, stronger zephyr winds are expected
with gusts 25-30 kt.

Record heat through Friday will contribute to enhanced thermals and
turbulence into and out of area airports especially at KRNO.
Also, the heat will raise density altitude levels possibility
impacting aircraft performance during peak afternoon heating. Max
temp of 105 projected at RNO both days would yield density
altitude around 8000 feet MSL during the 22z-01z timeframe. MJD

&&

.REV Watches/Warnings/Advisories...
NV...Fire Weather Watch from Friday afternoon through Friday evening
     NVZ458.

     Red Flag Warning from 2 PM to 9 PM PDT Friday NVZ450-459.

     Heat Advisory until 11 PM PDT Friday NVZ001-004.

CA...Fire Weather Watch from Friday afternoon through Friday evening
     CAZ270-271-278.

     Red Flag Warning from 2 PM to 9 PM PDT Friday CAZ273.

&&

$$

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


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