Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 150327 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
827 PM PDT Fri Jul 14 2017

.UPDATE...
Thunderstorms have ended with satellite imagery showing clouds
decreasing as well. So the threat of convection is over the the
night. Storms stayed east of the Sierra foothills as the afternoon
zephyr was a bit stronger and able to shunt outflow from storms
that developed along the Pine Nuts and Virginia Range. Winds are
expected to gradually decrease this evening with light winds
overnight into early much of Saturday. Therefore areas that are
currently seeing smoky air will likely remain smoky overnight into
Saturday morning as the atmosphere decouples. Updates out soon.
Hohmann


&&

.SYNOPSIS...

Isolated showers and thunderstorms will be limited to areas south
of Highway 50 this weekend. Thunderstorm chances are slim next
week as drier air arrives. Gusty winds are expected Monday and
Tuesday.


&&

.PREVIOUS DISCUSSION... /Issued 139 PM PDT Fri Jul 14 2017/

SYNOPSIS...

Isolated showers and thunderstorms are possible through this
evening mainly from I-80 southward, then become limited to areas
south of Highway 50 this weekend. Thunderstorm chances are slim
next week as drier air arrives. Gusty winds are expected Monday
and possibly Tuesday, with more typical breezes expected later
next week.

SHORT TERM...

With weak flow aloft and a modest zephyr later today, thunderstorms
are expected to develop near the Sierra and into western NV later
this afternoon through this evening. We also expanded isolated
thunder a bit farther north into southeast Lassen County
(including the Long Valley fire area) as this area tends to be
favorable for a few cells in this pattern, even with just a weak
signature of instability and low level convergence on model
guidance. There is little forcing outside of afternoon heating,
and instability is not particularly strong, which should limit the
intensity and duration of these storms. Slow cell movement could
lead to moderate to heavy rainfall and small hail in a few
locations, along with lightning strikes outside of the
precipitation cores and outflow winds of 40-50 mph.

For this weekend, the overall trend continues to reduce
thunderstorm potential and coverage, with isolated thunder limited
to areas south of US-50 and east of the Reno-Carson Tahoe regions,
as air mass becomes more stable to the north. Cells are again
likely to be mainly pulse type with similar threats/impacts as
today`s activity. The only other notable feature is a band of mid
level moisture spreading north across the Sierra and western NV
Saturday night and early Sunday from a remnant tropical system,
with model guidance generating light precip especially near and
east of US-95, but also as far west as the Reno-Tahoe regions. We
continued to mention possible light rain showers in these areas,
but instability still looks too weak for a meaningful threat of
thunder. The cloud cover will hold temperatures up with some
valleys not dropping below 70 degrees early Sunday.

Outside of thunderstorms, winds will be generally light through
Saturday with afternoon gusts topping out around 20 mph, then
gusts trend upward a bit to near 25 mph by Sunday. Temperatures
will remain above average, with upper 90s to near 100 degrees for
the lower valleys. MJD

LONG TERM...Monday onward...

Dry and stable air mass now looks to prevail through next week
with thunderstorms unlikely, although some afternoon cumulus is
probable especially south of US-50 later next week. Temperatures
will ease downward a bit on Monday, then remain in the 90s for
lower elevations and lower-mid 80s near the Sierra through Friday.

Next week will begin with gusty winds as a shortwave trough moves
across the Pacific Northwest coast while combined with a jet
segment moving through northern CA/NV. This combines with a drier
air mass will lead to increased fire danger on Monday. Please see
the fire weather section below for additional details. The winds
will also create choppy conditions on area lakes Monday afternoon
and evening.

For Tuesday, moderate southwest flow aloft and a weaker secondary
shortwave moving across far northwest CA could bring another
breezy afternoon and evening with continued dry conditions,
although speeds should drop off a little from Monday. From
Wednesday-Friday, lighter southwest flow aloft will lead to more
typical late day zephyr-type breezes.

By the weekend of July 22-23, there are indications that the
ridge over the Desert Southwest could expand across the Great
Basin, sending valley temps up toward the triple digits again.
There is more uncertainty for thunderstorm potential as some
guidance scenarios keep the ridge axis south of western NV (dry
with capped cumulus) while other scenarios expand the axis
northward across the Great Basin (isolated thunder threat). MJD

AVIATION...

Isolated showers and thunderstorms could develop as far north as
eastern Lassen County-Pyramid Lake-Lovelock this afternoon and
evening. Chances are low (only about 10%) that a storm will pass
directly over any of the main Sierra or western NV terminals so we
did not include a mention of thunder. Outflow wind gusts up to 40
kts and lightning are a possibility with any storm that does
form. Cloud bases are likely to be fairly high, leading to a low
risk of terrain obscuration or conditions dropping below VFR.
Chances for showers and thunderstorms continue each afternoon and
early evening through the weekend, but should mainly be limited to
areas south of US-50 and east of Tahoe (for the main terminals,
this would only include KMMH).

Modest west winds of 10-15 kts gusting to 20 kts can be expected
each afternoon and early evening today and Saturday, with slightly
stronger winds for Sunday. Winds are expected to increase further
on Monday, leading to areas of moderate turbulence east of the
Sierra. MJD

FIRE WEATHER...

After some isolated convection today through the weekend and the
potential for some new fire starts, increasing winds combined
with a significant dry slot are likely to produce critical fire
weather conditions on Monday. Winds could gust to 30-40 mph along
with single digit minimum humidity values for portions of
northeast California and northwest/west central Nevada, where
Fire Weather Watches have been issued. Of greatest concern is the
fact these winds will be following a few days of thunderstorm
activity over the weekend and any new starts will have the
potential to rapidly grow. These breezy and dry conditions will
likely repeat Tuesday, but winds may be more on the marginal side.

Thunderstorm coverage does not look as widespread for the weekend as
previously forecast, but storms are likely to be a hybrid of wet and
dry as moderate storm motions will limit precipitation totals
outside of the main rain core. Dry lightning strikes could
potentially ignite new fires across the region ahead of Monday`s
critical conditions. The best chances for thunderstorms the next
few days will mainly be south of Highway 50. -Dawn/Boyd

&&

.REV Watches/Warnings/Advisories...
NV...Fire Weather Watch from Monday afternoon through Monday evening
     NVZ450-453-458.

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

&&

$$

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



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