000
FXUS65 KREV 092141
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
241 PM PDT Sun Aug 9 2020

.SYNOPSIS...

Isolated thunderstorms are expected through early evening near the
Sierra. Storms spread more into western Nevada and northeast
California Monday and Tuesday, with increasing breezes bringing fire
concerns Tuesday and Wednesday. Daytime temperatures will be near to
just above normal this week, with a period of cooler morning lows
mid to late week as drier air moves in.

&&

.DISCUSSION...

* Changes: Added low-end potential for a few storms each day
  Friday-Sunday over the mountains.

* After today`s isolated storms over the Sierra, things continue
  to look busier t-storm wise for Monday and Tuesday as moisture
  levels rise into a sweet spot of 0.6 to 0.8" precipitable water.
  Calibrated guidance from HREF and NBM show this trend nicely.
  Large area of 50%+ t-storm chances in HREF for Monday afternoon.
  Monday the main threat is heavy rainfall - storm motions look
  quite minimal. Will definitely need to watch recent burn scars
  for enhanced flash flood potential. For Tuesday storm motions
  and shear increase as a trough digs into the Pac NW. This leads
  to greater risk for a couple stronger storms with hail and big
  outflows, but also new fire starts as storms won`t linger over
  the same areas too long.

* Drier air works in Wednesday with t-storms focused in typical
  convergence zones such as Mono-Mineral. With trough passing by,
  the gradient picks up just enough for enhanced zephyr winds
  especially I-80 and northward. This may result in areas of
  critical fire weather. Read more in the fire weather discussion if
  you so desire. No appreciable travel or recreation impacts from
  the wind however. Drier air will allow night temps to drop more
  Wednesday-Friday with some refreshingly cool lows to counter warm
  daytime temps.

* Dry air doesn`t last too long, as latest ensemble guidance is
  now starting to show moisture from E Pac tropical cyclone(s)
  working northward into CA/NV Friday-Sunday. Roughly 70% of the
  ECMWF EPS members bring up PW values sufficient for storms. As a
  result, we`ll probably see at least isolated t-storms return to
  the mountains and maybe valleys during that period, but
  coverage and intensity is TBD. Of course impacts range from new
  fire starts to flash flooding.

-Chris

&&

.AVIATION...

Mainly VFR conditions for the remainder of the day at all area
terminals with a west-northwest breeze through this evening.
Daytime temperatures will be at their warmest today which could
lead to some thermal bumps and density altitude concerns,
especially for KLOL, NFL, KRNO, KCXP, and KMEV. Isolated
thunderstorms are likely to form along the Sierra Crest this
afternoon with a 10-15% chance for one to impact KTVL and KTRK.
Erratic outflow winds, lightning, small hail, brief downpours, and
mountain obscuration could accompany any storms that do form.

Have added patchy fog for KTRK overnight lasting to around 14Z on
Monday all depending on if this site does receive any additional
precipitation from this afternoon`s thunderstorm activity.

Thunderstorm coverage increases for Monday and Tuesday
afternoon`s bringing scattered chances the Sierra and far western
Nevada sites on Monday and to all area terminals on Tuesday as
coverage shifts more eastward. The common thunderstorm impacts to
aviation are likely during this time, including strong outflow
gusts and possible blowing dust for KLOL, NFL, and KHTH.
-LaGuardia

&&

.FIRE WEATHER...

No changes were made to the fire weather forecast this afternoon
with previous thinking on track. Have left the Fire Weather
Watches in place for northeast California, the Sierra Front,
northern Washoe County, and Pershing County for Tuesday afternoon
through Wednesday thanks to the dry lightning potential and gusty
winds.

Isolated thunderstorms are possible once again this afternoon mainly
along the Sierra Crest from northern Mono County to just north of
the Tahoe Basin. Coverage increases Monday and Tuesday as
precipitable water values reach into the 0.6-0.8 inch range. There
is a lesser threat for new fire starts on Monday as convective
models show slower storm motions leading to an increase in wetting
rains. Confidence has grown in Tuesday afternoon featuring faster
storm motions and a higher threat for dry lightning and gusty
outflow winds possibly contributing to new fire starts with best
chances for areas mentioned previously. Some ensemble models are
starting to show an increase in gradient winds on Tuesday as well,
mainly for locations north of I-80, as drier air begins to move
through from the west. This would ultimately increase already
heightened fire concerns in the region.

Much drier air pushes its way into the Sierra and western Nevada
region on Wednesday accompanied by an enhanced zephyr wind. This
combination (plus possible lightning holdovers from Tuesday) is
forecast to generate critical fire weather conditions from the
Sierra Front northward into northeast California and northwest
Nevada. As of now, confidence is highest for locations north of I-80
from Susanville-Gerlach-Lovelock-Winnemucca to see these critical
conditions on Wednesday. -LaGuardia

&&

.REV Watches/Warnings/Advisories...
NV...Fire Weather Watch from Tuesday afternoon through Wednesday
     evening NVZ420-423-458.

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

&&

$$

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