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fxus65 krev 200938 

Area forecast discussion
National Weather Service Reno Nevada
238 am PDT Sat Jul 20 2019

mid-Summer heat will persist across the Sierra and western Nevada
for the upcoming week, with highs reaching 100 degrees in some
valleys. Isolated thunderstorms with little or no rainfall are
possible each day through Monday, then conditions become more
favorable for thunderstorms which could produce locally heavy
rainfall for much of next week, mainly south of I-80.


Short term...

The overall forecast remains intact with high pressure ridge over
The Four Corners region expanding across much of the Great Basin
during the next couple of days. This will lead to additional
warming, especially Sunday-Monday when temperatures are likely to
reach their peak values. For these days, it's about a 50/50
chance for Reno to reach 100 degrees for the first time this year,
but almost a sure bet that most valleys in west central Nevada will
see some triple digit highs. Overnight lows will also creep
upward, with some sites remaining above 65 degrees through early
next week.

For today, weaker flow will help set up convergence along the
Sierra crest, while some mid level cooling brings some increased
instability. Some of the model/ensemble data sources continue to
indicate the potential for isolated thunderstorms for mid-late
afternoon in portions of alpine and Mono counties near the crest.

From Sunday afternoon-Monday night, there is still a potential
for isolated thunderstorms producing little to no rainfall and
strong outflow gusts. However, it's not a certainty that all of
the ingredients needed for high-based daytime thunderstorms, and
elevated convection at night will come together. Subtle features
such as the location and track of weak upper level disturbances,
areas of increased mid level moisture, and enhanced lift due to an
upper level wind maximum will determine whether (and where)
thunderstorms will develop. For more details on this thunderstorm
potential, currently favored locations, and the primary impacts,
please see the fire weather segment below. Mjd

Long term...Tuesday Onward...

No major changes to the long term part of the forecast. Large
scale pattern still has a large area of high pressure across the
southwest US, with troughs moving through the Pacific northwest
flattening the ridge somewhat for extreme northern California/Nevada the first
half of the week. This will keep temperatures near to slightly
above normal with daily chances for thunderstorms. Storm activity
is likely to be focused near and south of I-80, with areas to the
north still influenced by drier southwesterly flow due to the
trough passages.

Thunderstorms will be transitioning to wetter as the week
progresses with localized heavy rainfall becoming possible. Gusty
winds will still be a threat along with small hail. Anyone with
outdoor plans next week should pay careful attention to the
forecast and have a way to get weather alerts to avoid being
caught off guard.

Ensemble guidance is hinting at the ridge becoming better
established by the end of next week across the entire west, which
could bring temperatures back to near or above the triple digit
mark in lower valleys. This will also allow thunderstorm
development farther north, with thunderstorm chances expanded to
reflect this the end of next week. -Dawn



VFR conditions today with a 15% chance of thunderstorms along the
Sierra crest from ktvl to kmmh between 20-03z. Westerly afternoon
breezes will be lighter than usual, with peak gusts in the 12-20
kt range. Hot surface temperatures of 95-105 in western Nevada
valleys and mid to upper 80s in Sierra valleys could bring density
altitude concerns through the weekend.

As the pattern begins to shift, afternoon thunderstorms become
more likely into next week. Greatest threats this weekend will be
gusty and erratic outflow winds along with turbulence due to the
convection. By the middle into the end of next week, lowering
ceilings/visible from locally heavy rain, especially south of I-80,
becomes more likely. The other concern is the potential for mainly
dry nocturnal storms Sunday night and Monday night in northeast California
into portions of western Nevada. -Dawn


Fire weather...

Interesting week ahead with increasing thunderstorm threat and
gusty and erratic outflow winds possible.

High based thunderstorms are possible today along the Sierra crest
between Mammoth and South Lake Tahoe, expanding north and east on
Monday. There won't be much moisture to work with yet, so dry
strikes outside of small rain cores are quite possible. The high
bases along with hot afternoon temperatures brings the threat of
strong outflow winds -- likely 45+ mph. Even building and
collapsing cumulus, which do not fully develop into a
thunderstorm, could produce gusty winds.

The other concern is the possibility for nocturnal storms Sunday
and Monday nights. The region is between a trough in the Pacific
northwest and a ridge over the Desert Southwest with a jet streak
between these features in northeast California into northwest Nevada.
Latest thinking is the best chances for storms Sunday night would
be for northeast California into northern Washoe County and
possibly southeast Oregon. Then Monday night, the threat shifts
slightly eastward, with chances expanding into Pershing County as
well. Storm motions are fast (25-30 mph) and there is little
moisture to work with. This doesn't appear to be a major dry
lightning outbreak, but even a few storms can easily ignite new
fire starts.

While winds overall will be lighter than the typical 20-30 mph,
the one exception will be along the northern Sierra front into
Lassen and northern Washoe counties due to the jet overhead. Peak
gusts here could easily reach 30 mph Monday and Tuesday, which
could be a concern following the possible dry thunderstorms the
nights before.

Otherwise, the thunderstorm risk remains through the week, with
the greatest coverage likely to be south of I-80 and less than a
10% chance in northeast California/extreme northwest Nevada through
Thursday. Storms will be transitioning wetter as the week
progresses with localized heavy rainfall possible. Storms could
expand farther north by the end of the week or next weekend. -Dawn


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