Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 222034
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
134 PM PDT Sat Jul 22 2017

.SYNOPSIS...

Areas of haze from the Detwiler Fire could return this weekend,
mainly in the Sierra mountains and along the Sierra front range.
Thunderstorms are expected to develop each afternoon Sunday
through Tuesday or Wednesday. Some of the thunderstorms on Sunday
will be on the drier side, before more moisture arrives Monday
and Tuesday with wetting rains and localized flash flooding
possible.

&&

.SHORT TERM...

The short term forecast remains on track with chances for high-
based thunderstorms tomorrow afternoon as a Pacific low pressure
approaches the CA coast. This approaching low will lead to
increasingly moist southerly flow along with steep upper-level
lapse rates around 8.0 C/km tomorrow afternoon/evening.
Thunderstorm motions 10-20 mph, high cloud bases, and smallish
rain cores are expected with most storms. Thus, lightning strikes
outside of rain cores are likely to start new fires and
thunderstorm outflows could produce gusts in the 45-60 mph range.
A Red Flag Warning for the east Sierra and western NV is in effect
for Sunday afternoon/evening. See the Fire Discussion below for
additional details.

The Detwiler fire west of Yosemite Park is not burning as actively
today and downwind air quality has improved. Smoke trajectory
models indicate some light haze could move back into the Sierra
this evening, possibly settling into Sierra front range valleys
tonight, but this haze should be much less thick than earlier in
the week.

For Monday, moisture continues to increase over the Sierra and
western NV, although drier storms could still be possible north
of Susanville. Storm-depth shear and upper forcing will also
increase as impulses move from south to north while the upper low
moves inland over northern CA. These conditions are likely to
create stronger, wetter storms Monday compared to Sunday. Flash
flooding is a possibility, especially on recently burned areas
including along I-80 between Sparks and Fernley (the Earthstone
burn scar).

High resolution models suggest Lassen Peak convergence may be an
active zone of thunderstorm initiation across Lassen county Monday
afternoon.

Low pressure remains centered along the Northern CA coast on
Tuesday, bringing another series of upper level impulses through
northern CA/NV Tuesday afternoon. This will expand thunderstorm
coverage and even bring some organization to the thunderstorms as
a diffluent zone moves overhead. Thunderstorms on Tuesday could
include threats of flash flooding, small hail, damaging winds, and
localized heavy rainfall. With precipitable water values expected
around 1 inch, much of the thunderstorm development could depend
on breaks in the clouds. If skies become overcast too early in the
day, thunderstorms won`t be as strong and coverage could be less.
JCM

.LONG TERM...Wednesday through Sunday...

Low pressure lifts out of the area on Wednesday, with drier
southwest flow returning to the region. However, there could be
enough lingering moisture for isolated, weaker showers or
thunderstorms. Typical breezy afternoon winds will return with
temperatures cooling off a bit to near average mid week.
Temperatures will start to increase again by the end of the week
as the ridge strengthens. A weak moisture surge could begin
Saturday, with showers and thunderstorms possibly returning on
Sunday. JCM

&&

.AVIATION...

VFR conditions today with areas of haze possibly returning from
fires in California. Typical breezy west winds expected this
evening with gusts up to 20kts.

Thunderstorm potential increases Sunday through Tuesday with
scattered showers and storms possible each afternoon and evening.
The usual threats of gusty outflow winds, small hail and locally
heavy rains will apply. JCM

&&

.FIRE WEATHER...

Hot and dry conditions today will give way to increasing moisture
through Tuesday. Mid and high level moisture will increase
tonight with lower level moisture lagging a bit. Thunderstorms are
expected to begin tomorrow and continue into Tuesday and possibly
Wednesday.

With the moisture more limited at lower levels tomorrow, the Red
Flag Warnings look good. Hot conditions with one more day of low
RH will keep fuels susceptible to new starts, especially those
outside of rain cores. The storms will start dry and begin to
transition to wetter storms by evening. Still, ignition efficiency
is likely to be high with numerous new starts likely. Outflow gusts
to 50 mph, and possibly 60 mph in the deserts will be capable of
rapidly spreading new starts.

Monday will see a transition to wetter storms for most of the area
with localized flash flooding becoming possible, especially over
recent burn scars. The question is up north where the models are now
slower to increase the moisture. In fact, they show drying Monday
over Sunday. This looks unreasonable as moisture typically pools
south of the deformation zone. All areas will be south of the area
of deformation so expect moisture to increase all areas. Tuesday
will see moisture increase even further with very wet storms as PWAT
nears 1 inch. Wallmann

&&

.REV Watches/Warnings/Advisories...
NV...Red Flag Warning from 3 PM Sunday to midnight PDT Sunday night
     NVZ450-453-458.

     Red Flag Warning from 1 PM to 9 PM PDT Sunday NVZ459.

CA...Red Flag Warning from 3 PM Sunday to midnight PDT Sunday night
     CAZ270>272-278.

     Red Flag Warning from 1 PM to 9 PM PDT Sunday CAZ273.

&&

$$

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



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