Wildfire in California, September 4 to 25, 2019

Area Forecast Discussion
National Weather Service Reno NV
351 AM PDT Wed Sep 4 2019

.SYNOPSIS...

Increasing moisture will bring more widespread coverage of
showers and thunderstorms today through Thursday. Stronger storms
could produce strong outflow winds, frequent lightning, and
localized flash flooding. Dry conditions move in Friday, with
breezy conditions Saturday and a notable cooling trend for Sunday.

&&

.SHORT TERM...

Currently, light showers are moving northward across the west
central NV Basin and Range (producing trace rainfall over parts of
Fallon), and are likely to continue through this morning with
isolated lightning strikes possible after daybreak.

For the rest of today, widespread moisture and increasing
instability will lead to development of scattered showers and
thunderstorms this afternoon. There will be an opportunity for
some thunderstorms to initially become strong and produce small
hail and locally heavy rainfall. While cell motion is likely to be
faster than yesterday's storms, there could be some cells
training over the same locations, especially over Mono-Alpine
counties and from southern Douglas to southern Mineral counties.
The storm activity is projected to progress northward across
western NV for the late afternoon-evening, with additional
isolated showers and storms forming in northeast CA-northwest NV.
Abundant cloud cover may transition the thunderstorms to areas of
rain showers with only isolated lightning as we get into the late
afternoon-early evening hours.

For tonight, an upper level disturbance moving across northern CA
is likely to keep scattered showers and isolated thunderstorms
going into early Thursday morning. Much of the guidance is in
agreement with the most favored areas including northeast CA
between Truckee and Susanville, and also parts of northwest and
far western NV generally from Reno northward.

Flow increases Thursday as the main trough begins to move inland
along the northern CA/OR coast, with storms rapidly tracking to
the northeast by the afternoon. Shear is fairly unidirectional,
which means a better chance for storms to train over the same
location. The increased deformation due to the trough, along with
the shear and likely outflow interactions means that Thursday has
a greater potential for strong/severe storms, especially across
much of western NV north of I-80. If you have outdoor plans, be
sure to have a way to get weather alerts and keep a close eye on
the sky.

After these storms exit the region Thursday evening, drier and
more stable conditions return for Friday with typical afternoon
breezes. There isn't much cooling behind this initial trough
passage though, with highs expected to remain above average
(around 90 degrees for lower elevations, and around 80 near the
Sierra). MJD

.LONG TERM...Saturday through next week...

A deeper, sharper trough will move into California and Nevada by
this weekend with the main impact of bringing widespread gusty
winds on Saturday. These winds will likely impact lake recreation
and aviation, as well as potential for elevated fire weather
concerns. When the cold front moves through late Saturday
afternoon into Sunday morning, we could see some showers and even
a slight chance of thunder with the dynamic forcing.

The good news--this cold front will bring the first cool down of
September. This will bring temperatures down to "early fall", which
will be a nice reprieve of the consistent heat we've been seeing.
Temperatures will drop below normal on Sunday with highs in the
70s across western Nevada and 60s in the Sierra.

These cooler temperatures rebound modestly into next week, but
expect to see a gorgeous week with mostly sunny skies and highs in
the lower 80s for western Nevada and 70s in the Sierra and
northeast California. Crisp early morning temperatures may even
drop below freezing for some colder valleys in the Sierra, so you
may want to keep an eye on the forecast lows for your gardens
Monday morning. -Alex

&&

.AVIATION...

Forecast concerns continue to focus on thunderstorm chances today
through Thursday. Storms may bring brief heavy rainfall, small hail,
and strong erratic outflow winds.

Today remains the greatest wild card, due to atmospheric moisture
values around 200% of normal for this time of the year. Sometimes
this leads to extensive cloud cover with less storm potential,
but if we remain clear, storms with heavier rain become more
likely bringing low ceilings and visibility, obscuring terrain.
The potential for these stronger storms is favored in areas south
of Minden-Hawthorne, including the eastern Sierra and the KMMH
terminal.

Storms Thursday could be stronger as a trough moves into the
region, but will also quickly move off to the northeast in the
afternoon, due to increased flow as a trough moves inland. Areas
of western NV north of I-80 currently have the highest storm
potential, with a secondary band possibly impacting eastern parts
of Mono-Mineral counties. MJD

Chances for storms to impact terminal sites today/Thurs:

KRNO/KCXP: 25/40%
KMEV/KTRK/KTVL: 20/30%
KMMH: 60/40%

&&

.FIRE WEATHER...

Thunderstorm activity increases this afternoon with faster cell
motions compared to Tuesday, although moisture will also be
abundant. So while lightning ignitions outside the rain cores are
possible, the coverage of them should be limited.

For tonight, additional lightning strikes are possible across
northeast CA-far northwest NV in association with a weak upper
level disturbance. This setup would be more of a concern if the
lower atmosphere was dry and forcing was greater, due to
relatively fast cell motion and shorter duration of rain. However,
forcing and elevated instability are limited so the potential for
significant lightning activity is low.

For Thursday, thunderstorms could become more intense, with a few
severe, long-lived storms possible as upper forcing arrives for
northeast California and northwestern/western Nevada. The stronger
storms could bring copious lightning, especially north of
Interstate 80, but they will also contain heavy to possibly
torrential rains given the deep moisture. As far as winds Thursday
afternoon and evening, they don't look to be very strong (except
near thunderstorms) and humidity values should be well above 20
percent even behind the thunderstorm activity.

Drier conditions return Friday, but afternoon breezes look to be
of the typical gusts of 20-25 mph. For Saturday, winds increase
ahead of a stronger trough passage. Isolated spots with brief
near critical or critical conditions are possible. MJD

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

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