Wildfire in California, July 10 to 12, 2017

Area Forecast Discussion
National Weather Service Reno NV
244 AM PDT Mon Jul 10 2017

.SYNOPSIS...

Increased winds and dry conditions prevail today which will
result in critical fire weather concerns and choppy boating
conditions across area lakes. Isolated showers and storms will be
confined to southern Mono and Mineral counties through Tuesday
with coverage spreading farther north by Wednesday. High
temperatures will drop a few degrees through Tuesday but will
heat up again by next weekend.

&&

.SHORT TERM...

A broad southwest flow aloft will usher in a very dry air mass
along with increased winds today. The combination of dry
conditions and gusty winds will result in fire weather concerns
today and Red Flag Warnings are in effect. See the Fire Weather
Discussion below for additional details. Stronger winds aloft have
arrived this morning with Slide Mountain reporting gusts of 40 to
50 mph. Winds aloft will peak this morning and will subside
through the afternoon hours. Valley locations will see gusts of
30+ mph this afternoon as mixing is enhanced. The gusty conditions
will also produce choppy conditions across areas lakes and Lake
Wind Advisories are also in place today.

An expansive dry slot can be seen on water vapor satellite imagery
across northern California and northwestern Nevada. This dry air
will confine isolated shower and storm activity to mainly south of
Mono and Walker lakes today and Tuesday. The moisture gradient
will shift farther northward into Lyon and Churchill counties by
Wednesday as upper level ridging nudges westward again.

Overall, temperatures will remain above season averages through
midweek but still down a few degrees from the triple digit heat
we experienced over the weekend. Lighter winds will also prevail
on Tuesday and Wednesday. Fuentes

.LONG TERM...Thursday through Sunday...

Subtle variations in the medium range models early in the forecast
and more significant differences between the models later in the
extended period have led to some minor tweaks to temperatures and
the introduction of thunderstorms for the weekend.

Thursday and Friday the four corners high is not building west as
fast as previous runs and the northern half of the forecast area
stays under drier southwest to west flow. This should confine any
chances for thunderstorms to south of Highway 50 and produce slightly
stronger low level winds...at least Thursday...for areas north of
Interstate 80. It could also mean highs a couple of degrees cooler
over the far northern forecast area. Thunderstorm chances creep a
bit farther north Friday and the winds are little lighter than
Thursday.

The high begins building west-northwest Saturday...but not with the
vigor shown by past model runs. Thus...temps aloft are not quite as
warm and instability may not be capped. We have added a slight
chance of thunderstorms for much of the Sierra and lowered high
temperatures a few degrees. Thunderstorm chances are mainly confined
to the western fringe of the high pressure. With a little less
thermal gradient...surface winds remain fairly light.

Sunday shows the greatest difference in the operational models. The
GFS is still building the ridge to the east with thunderstorm
chances increasing for the Sierra...far northeast California...and
western Nevada. In contrast...the ECMWF is developing more west-
southwest flow aloft and suppressing the ridge southeastward. This
would mean less chance of storms and cooler temperatures. Will lean
toward a compromise at this point and introduce slight of
thunderstorms for much of the CWA and also drop high temperatures a
few degrees.

The ultimate outcome in the far extended will be predicated on where
the ridge develops and how warm temperatures aloft become. Given the
inconsistencies seen so far...the forecast for this time frame is
likely to change...at least in minor ways...for the next few days.

&&

.AVIATION...

Areas of light to moderate mountain wave turbulence possible this
morning with wind gusts of 40-45 knots possible through about 18z
before diminishing through the afternoon. Increased winds are
expected this afternoon for valley terminals with gusts of 25-30
knots possible for KTRK/KTVL/KRNO/KCXP. South of Hwy 50 wind gusts
will be lighter and generally under 15-20kts. Lighter winds are
expected area wide on Tuesday and Wednesday.

Dry air aloft will confine shower and storm activity mainly south
of Mono Lake with about a 20-25% chance for TSRA at KMMH after
21z this afternoon. The main impact with any cells would be
strong outflow wind gusts up to 40-45 knots. Fuentes

&&

.FIRE WEATHER...

Winds and low relative humidity become the biggest concern over much
of the region today. An approaching upper level trough of low
pressure will provide just enough of an enhanced low level
pressure/thermal gradient for increased west-southwest winds...
mainly north of Highway 50 today. The strongest winds will likely
begin by late morning/early afternoon and last into the early
evening stretching from areas of northeast California east of
Susanville to the east and southeast along the Sierra Front and into
the western portions of the basin and range.

Sustained winds of 15 to 20 mph are likely this afternoon along and
east of the Highway 395 corridor from Susanville south to around
Walker with gusts approaching 35 mph. Lesser winds are likely south
and east of a line from Bridgeport to Yerington to Austin where the
gradient is not as strong.

A dry slot in the mid levels will mix to the surface in many areas
north of Highway 50 as well. The combination of gusty winds and low
humidity prompted the issuance of a Red Flag Warning for the
afternoon and evening for zones 278/458/450/453. Wind driven fires
in the heavy dry grasses could move very fast today.

To the south of Highway 50...especially south of a line from
Bridgeport to Austin...there will exist isolated thunderstorms with
the potential for gusty outflow winds and dry lightning today and
Tuesday. Thunderstorm chances may spread farther north Wednesday.

&&

.REV Watches/Warnings/Advisories...
NV...Red Flag Warning from 11 AM this morning to 11 PM PDT this
     evening NVZ450-453-458.

     Lake Wind Advisory from 11 AM this morning to 11 PM PDT this
     evening for Lake Tahoe in NVZ002.

     Lake Wind Advisory from 11 AM this morning to 11 PM PDT this
     evening for Washoe Lake in NVZ003.

     Lake Wind Advisory from 11 AM this morning to 11 PM PDT this
     evening for Pyramid Lake in NVZ004.

CA...Red Flag Warning from 11 AM this morning to 11 PM PDT this
     evening CAZ278.

     Lake Wind Advisory from 11 AM this morning to 11 PM PDT this
     evening CAZ071.

     Lake Wind Advisory from 11 AM this morning to 11 PM PDT this
     evening for Lake Tahoe in CAZ072.

&&

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