Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 262203
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
303 PM PDT Mon Jul 26 2021

.SYNOPSIS...

Monsoon moisture will overspread the region leading to an increase
in thunderstorm chances each afternoon much of this coming week.
Tuesday will be noticeably cooler before temperatures start warming
back up again late week. Smoke and haze will persist across eastern
Sierra and western Nevada while area fires continue into the week.

&&

.SHORT TERM

* A Flash Flood Watch has been issued until 9PM for possible brief
  heavy downpours at most recent and past burn scares over parts of
  the eastern Sierra.

A weak upper wave moving north-northwest through the region will
increase the forcing component for thunderstorm development during
the late evening and early morning hours over far western NV and the
eastern Sierra.  Smoke from our resident wildfires will play heavily
upon visibility and air quality considerations through much of this
forecast period.

* Smoke: There remains a mixed confidence on improving conditions
  through the the overnight hours based on T-storm outflows and
  limited  rainfall across the region.  With a change to a more
  predominate south- southeast upper flow the thunderstorm coverage
  will increase over the next few days.  Regional smoke patterns
  will likely change as well as increased outflows could disperse
  denser pockets of smoke in the area.

* Thunderstorms: Respectable monsoon moisture push into the region
  this week with a large high centered over the Four Corners and
  Rockies. Thunderstorm probabilities will remain elevated with
  precipitable water values rising to near 1" tomorrow afternoon in
  most ECMWF EPS members. Model solutions were mixed on the coverage
  of convection going into the evening but scattered coverage for
  the eastern Sierra into Mineral County remain a possibility as the
  shortwave approaches closer. A late arrival would mean that the
  earlier development of weaker cells and more clouds could limit
  coverage/intensity going into the evening. A wave lifting north
  out of SoCal could could keep faster moving t-storms going into
  the pre-dawn hours tomorrow morning. It is still expected that a
  combination of subsidence behind the outgoing wave and abundant
  PWATs could still limit storm coverage. By Wednesday, model
  guidance indications a piece of the offshore trough will lift over
  the region and combine with those more favorable elements of less
  cloud cover/decreased PWATs to bring on more robust thunderstorm
  development across the Sierra and western NV.

* We`ll really need to be on our toes with flash flood and debris
  flow risks on the newer burn scars such as Beckwourth, and even
  the ongoing Tamarack Fire especially on steeper slopes just west
  of Hwy 395 and steep terrain of Alpine County. It only takes 5-10
  minutes of heavy rain to cause major flooding on recent high
  intensity burns. Will continue to monitor on a daily basis with
  regard to whether a flash flood watch is needed, as flood flood
  environments have limited predictability in our region more than
  12-18 hours out. Hohmann/Amanda

.LONG TERM...Thursday onward...

Thunderstorm chances continue Thursday, but lesser coverage is
anticipated compared to Wednesday due to lack of large scale
forcing. Storms are likely to be of the more pulse variety with
localized heavy rainfall, gusty outflow winds (which could kick up
areas of dust), and the potential for small hail. The ongoing
lightning risk could still cause new fires, but due to the overall
wetter nature of the storms, it`s much less likely for fires to make
runs.

Thunderstorm coverage looks to increase Friday and with an increased
risk on Saturday.  A weak short wave moving through the area could
increase forcing but it will be weak at best. Nonetheless,  PWATs
increasing and hovering within the 0.5-0.8" sweet spot along with
relatively slow storm motions due to weak upper divergence over the
region will increase flash flood concerns for Saturday. The recent
burn scars and ongoing wildfires will be the main focus or concern.
Showers could continue Saturday night, with low end chances for an
embedded thunderstorm or two.

The increasing dry southwest flow from the trough along the northern
CA coast will begin to push moisture more east Sunday into Monday.
This will lead to less thunderstorm coverage, with chances really
waning by Monday. We`ll also see the return of more typical westerly
afternoon breezes and decreasing humidity values around August 2-3.

Daytime highs next week will be within a few degrees of normal,
varying day to day based on thunderstorm coverage and time of storm
initiation. Nights will remain mild due to the increased moisture.
We`ll have to see how thunderstorms impact the wildfires as rain and
outflow winds will both be big contributors to smoke and air quality
impacts. -Dawn/Amanda

&&

.AVIATION

Thunderstorm chances will continue region-wide overnight with
periods of brief downpours, frequent lightning, and gusty outflow
winds.   The main focus will be directed mostly in the Sierra into
northeast California. The heaviest rainfall will likely be the areas
near KMMH north to lake Tahoe. Sufficient upper moisture will ensure
thunderstorm chances continue daily through next weekend.

Going into Tuesday smoke trajectories will chance as a south to
southeast upper flow increases across the region.  Unknowns such as
rainfall and erratic outflow winds with play heavily as to any
possible VSBY outcomes across the region  Therefore any smoke
forecast brings much lower than usual confidence through the
forecast period. VSBY forecasts will weigh heavily towards higher
resolution smoke models. Periods of MVFR conditions should influence
VSBY forecasts for KMEV-KCXP-KRNO through tomorrow morning.  This is
due mostly to the close downwind proximity of the Tamarack and
especially Dixie wildfires which at this time continues to produce
heavier smoke plumes. As the prevailing upper flow increases from
the south  later this evening into the early morning hours all other
terminal should see any restrictions from VSBY/CIG gradually
improving to mostly VFR.  KMMH will continue to be spared from the
ongoing concerns centering around the smoke and haze issue. -Amanda

&&

FIRE WEATHER...

Areas of showers and thunderstorms will continue this evening mainly
south of Hwy 50 through Mono and Mineral counties as a shortwave
trough tracks across southern Nevada. Thunderstorm outflows tracking
from south to north are possible as storms develop across Mono-
Mineral with outflows up to 45 mph reaching as far north as I-80 by
9-10pm this evening.

Thunderstorm potential should wane this evening after about 2200
local with a transition mainly to bands of showers with a few
isolated lightning strikes not out of the question as bands track
across the Tahoe Basin into Lassen County. While RH recoveries will
generally reach 45-50% overnight across Sierra mid-slope locations,
recoveries could be boosted defendant on this evening precipitation.

Monsoon moisture will maintain shower and thunderstorm chances
through the week with the best potential Tuesday mainly confined to
southern Mono and Mineral counties. Coverage looks to become more
widespread on Wednesday as less cloud coverage may lead to be better
surface heating and instability which combined with a shortwave
trough may lead to better organized and potentially stronger
thunderstorms. These storms will be a little faster moving but with
ample moisture storms will be efficient rain producers and capable
of flash flooding and debris flows on area burn scars, especially
where storm cells train. Gusty outflow winds with sudden wind
shifts, hail, and cloud to ground lightning will be possible with
these storms. Fuentes

&&

.REV Watches/Warnings/Advisories...
NV...Flash Flood Watch until 9 PM PDT this evening Nvz001-003.

CA...Flash Flood Watch until 9 PM PDT this evening Caz071-073.

&&

$$

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


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