Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 161100

Area Forecast Discussion
National Weather Service Reno NV
400 AM PDT Wed Aug 16 2017


Weak trough across the west will allow for light winds as well as
temperatures near to slightly above average through the week.
Thunderstorms will be possible from Mono County to the Tahoe
Basin today and in Mono County Thursday as instability will be
best there. Thunderstorm chances and coverage will expand across
the rest of the Sierra and Western Nevada for the weekend.



Changes made to the previous forecast were modest and primarily
concerned spreading isolated afternoon thunderstorms into the
Tahoe Basin and along the Pine Nut range. Instability resulting
from afternoon heat, lack of a mid-level cap, and a weak trough
aloft will aid in increasing the extent of thunderstorm coverage
over what was previously forecast.

Otherwise, the forecast remains on track. A few lingering showers
are occurring mainly in the Basin and Range on the heels of a weak
trough that will be slow to exit the region today. General
troughing will remain over Nevada and northeast California through
the short term forecast. However, a weak extension of the ridge
will likely limit convective development south of Alpine County
along the higher Sierra for Thursday.

West coast troughing is projected to deepen Friday resulting in a
larger areal extent of isolated thunderstorms. Chances will extend
north of Interstate 80, but will likely remain south of
Susanville as troughing develops into an upper low circulation
over California. Coverage of isolated thunderstorms will extend
along and east of the Sierra Front including Pyramid Lake and
portions of Mineral County.

The flow pattern over the next few days will generally be
northerly and relatively light, but late afternoon winds increase
and shift westerly as weak zephyr winds form. This should allow
for improving air quality for Mono County, but smoke/haze remains
largely dependent on fire activity and may seep through valleys
overnight. Temperatures will range around seasonal averages to
slightly above average into the weekend. Boyd

.LONG TERM...Saturday through Tuesday...

A few minor changes were made to the extended forecast. These
changes mainly involved increasing coverage of showers and
thunderstorms a bit more for Saturday through Monday.

The medium range model guidance is still trending toward a wetter
period for the weekend and early next week. An upper low develops
along the coast...but the GFS remains more aggressive with its
evolution than the ECMWF. The GFS even cuts the low off by Sunday
and slides it farther down the coast. Meanwhile...the ECMWF holds
more of an open wave/broad trough over the region. By late Tuesday
the GFS lifts the low northeast across southern California.

The presence of this low to the west should allow for an increase in
return flow from the south that would pull more moisture north into
the region. This increase in moisture combined with heating and
instability aloft should result in showers and thunderstorms each
day. The best coverage now looks to be Sunday...but confidence in
coverage on any day is only low to moderate. increasingly wet pattern is likely this weekend and
early next week. Storm motions should be fairly slow allowing for
wetting rains to develop in the stronger storms.



VFR conditions will prevail for all TAF locations. MMH and TVL
could see isolated thunderstorms today, but lower confidence will
keep them out of the TAF. Elsewhere, cumulus will develop,
potentially to moderate extent. Coverage of thunderstorms will
lessen Thursday as weak ridging extends over the northern Sierra;
KMMH may see a few isolated cells. Coverage then expands Friday
including all terminals in the Sierra and along the Sierra Front
south of Susanville. More thunderstorms with overall wetter
conditions are anticipated for the weekend.

Haze and smoke at MMH will continue to degrade slant-wise
visibility slightly today, but a thunderstorm or two could clear
the air somewhat. Further develop of smoke and haze will be
largely dependent on fire activity, but flow patterns Thursday
and Friday suggest that smoke/haze will be kept along and west of
the Sierra crest. Boyd


.REV Watches/Warnings/Advisories...


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