Flash Flood Warning 17, NWS Reno, NV

952 
WGUS75 KREV 190225
FFSREV

Flash Flood Statement
National Weather Service Reno NV
725 PM PDT Fri Aug 18 2023

CAC003-051-NVC005-190235-
/O.EXP.KREV.FF.W.0017.000000T0000Z-230819T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Alpine CA-Mono CA-Douglas NV-
725 PM PDT Fri Aug 18 2023

...FLASH FLOOD WARNING FOR THE TAMARACK BURN SCAR WILL EXPIRE AT 730 
PM PDT THIS EVENING FOR ALPINE, NORTHERN MONO AND DOUGLAS COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat.

LAT...LON 3876 11965 3880 11964 3877 11956 3870 11951
      3862 11957 3866 11963

$$

HR

Area Forecast Discussion
National Weather Service Reno NV
217 PM PDT Fri Aug 18 2023

.SYNOPSIS...

Afternoon showers and thunderstorms prevail today and Saturday,
posing a threat of localized flash flooding. Attention turns
widespread, significant rainfall and potential flooding concerns
early next week as abundant moisture from Hurricane Hilary arrives
to the region.

&&

.SHORT TERM...

Latest radar observations reveals a few thunderstorms have developed
in the last couple hours with maturing cumulus along the higher
terrain. PWAT values are generally lower than they were this time
yesterday per 20Z mesoanalysis, which coupled with modest steering
flow, should reduce the overall flash flood potential today.
Additional shower and thunderstorm development will occur in the
next 4-6 hours before convective activity tapers off post-sunset.

Minimal change in the overall synoptic pattern will promote another
afternoon of showers and thunderstorms for Saturday, featuring a
likely uptick in coverage as rich moisture begins to trickle into
the region. As has been the case, wet thunderstorms will pose a risk
of localized flash flooding (especially in steep terrain and/or
where storm training occurs), cloud-to-ground lightning, and gusty
outflow winds. Blowing dust from gusty outflows may reduce
visibility in the Basin & Range. Be sure to have multiple ways of
receiving alerts if planning outdoor recreation this weekend!

CAMs have hinted at an initial wave of precipitation moving through
the region Saturday night into early Sunday morning before clearing
out after sunrise. A few rumbles of thunder cannot be ruled out,
though this is expected to be a prelude to things to come later in
the day on Sunday.

-Salas

.LONG TERM...

The long term forecast is still a rather challenging and exceedingly
rare one as the exact trajectory of now major Hurricane Hilary
remains variable. Latest guidance favors a slight eastward shift in
the trajectory, which would also displace the attendant moisture
plume further east as well.

With that being said, there is high confidence that anomalous
tropical moisture will travel northward in the coming days before
overspreading much of the Sierra and western Nevada in a south-to-
north fashion as soon as Sunday morning. As a result, significant
rainfall is forecast for a vast majority of the region during the
Sunday through Tuesday timeframe, with the greatest rainfall
accumulation favoring Mono and Mineral counties. Blended guidance
is certainly converging on a wetter solution with areas generally
south of the I-80 corridor now having a 20-40% chance of exceeding
1" of rainfall between Sunday and early Wednesday morning,
including the Greater Reno-Carson-Minden area and Tahoe Basin.
Areas north of the I-80 delineation generally have a 10-20% chance
of reaching an inch, though accumulations will likely remain in
the 0.5-1 inch range. The exception to this, of course, is Mono,
southern Lyon, and Mineral county where chances of surpassing an
inch of rainfall varies from 30-60% with a 10-30% chance of 2" of
rainfall accumulation. In the most extreme scenario, the southern
counties (Mono, Lyon, Mineral) have 5-15% odds of exceeding 3" of
rain. Locally greater totals will be likely for the higher terrain
due to upslope enhancement.

The fly in the ointment regarding rainfall totals will be heavier
rainfall rates from any thunderstorms. The current thinking is that
abundant cloud cover will dampen strong convection and limit the
thunderstorm potential. Probabilistic guidance suggests a 25-35%
chance of storms each day south of I-80, spatially coincident with
the area of greatest moisture availability. As such, locally greater
rainfall totals will be possible each afternoon Sunday through
Tuesday should thunderstorms develop.

Finally, a couple other noteworthy regional impacts from Hilary will
be: below average temperatures and gusty winds in the Basin & Range.
A potent cloud deck will yield high temperatures 10-15 degrees below
normal early next week. The other impact will be some gusty winds
Monday for extreme eastern Pershing, Churchill, and Mineral
counties. A bulk majority of the strongest gusts will remain east
of the region, although some gusts up to 40-50 mph will be
possible for these areas (10-20% odds per NBM).

-Salas

&&

.AVIATION...

* Expect a 30-40% chance for showers and thunderstorms to impact
  western Nevada terminals(KRNO,KCXP,KMEV) through 03z this evening
  followed by a 15% chance for isolated light showers from 03-06z.

* These storms on Saturday will be capable of producing gusty
  outflows to 40 kts with convective LLWS and turbulence possible
  anywhere outflows exist. Mountain range obscurations will also be
  possible due to cloud decks from storms, as well as localized
  heavy rain, small hail, and frequent lightning.

* Chances for more widespread showers and thunderstorms have trended
  higher for Saturday afternoon with development expected between 18-
  20z. By Sunday and Monday, there will be an increasing threat for
  moderate to heavy rainfall across the region due to remnant
  moisture from Hurricane Hilary streaming northward into the
  region. Fuentes

&&

.REV Watches/Warnings/Advisories...
NV...Flood Watch from Sunday afternoon through late Monday night
     NVZ001-004.

CA...Flood Watch from Sunday afternoon through late Monday night
     CAZ073.

&&

Special Weather Statement
National Weather Service RENO NV
259 PM PDT Fri Aug 18 2023

CAZ070>072-NVZ002-003-005-191200-
Surprise Valley California-Lassen-Eastern Plumas-
Eastern Sierra Counties-Greater Lake Tahoe Area-Greater Reno-
Carson City-Minden Area-Northern Washoe County-
Including the cities of Cedarville, Eagleville, Fort Bidwell,
Portola, Susanville, Westwood, Sierraville, Loyalton,
South Lake Tahoe, Tahoe City, Truckee, Markleeville, Stateline,
Glenbrook, Incline Village, Sparks, Verdi, Gardnerville,
Virginia City, Empire, and Gerlach
259 PM PDT Fri Aug 18 2023

...Shower and thunderstorm chances continue...
...Heavy rain with isolated flood potential Sunday-Monday...

* Showers and thunderstorms will continue to develop and push
  northward this afternoon and evening. These storms will be
  capable of gusts in excess of 45 mph, which could kick up dust
  from desert sinks and playas, in addition to localized heavy
  rainfall and small hail. Another round of scattered to
  widespread showers and thunderstorms will occur once again
  Saturday afternoon and evening.

* Major Hurricane Hilary in the eastern Pacific is expected to
  make landfall Sunday PM or early Monday AM along northern Baja
  of California or extreme southern coastal California. While this
  system will rapidly weaken into a remnant low by the time it
  reaches Nevada, significant amounts of moisture will bring
  periods of heavy rainfall to the region Sunday afternoon through
  Monday. The greatest threat for flooding is across the Basin &
  Range and the eastern Sierra. However, isolated flooding cannot
  be ruled out elsewhere across western Nevada and northeast
  California. Have multiple ways to receive alerts in case flood
  warnings are issued, and never drive through flooded roadways.

* Abundant cloud cover and rainfall will keep afternoon high
  temperatures 10 to 20 degrees below normal Sunday through
  Tuesday, with Monday likely being the chilliest day of the week.

* Stay tuned to the National Hurricane Center by visiting
  www.hurricanes.gov for the latest on Hilary.

CAZ073-NVZ001-004-191200-
Mono County-Mineral and Southern Lyon Counties-
Western Nevada Basin and Range including Pyramid Lake-
Including the cities of Bridgeport, Coleville, Lee Vining,
Mammoth Lakes, Hawthorne, Yerington, Smith Valley, Mina, Schurz,
Fernley, Fallon, Lovelock, Silver Springs, Nixon, and Imlay
259 PM PDT Fri Aug 18 2023

...Shower and thunderstorm chances continue...
...Heavy rain and flood potential Sunday-Monday...

* Another round of scattered to widespread showers and
  thunderstorms will occur once again Saturday afternoon and
  evening.

* Major Hurricane Hilary in the eastern Pacific is expected to
  make landfall Sunday PM or early Monday AM along northern Baja
  of California or extreme southern coastal California. While this
  system will rapidly weaken into a remnant low by the time it
  reaches Nevada, significant amounts of moisture will bring
  periods of heavy rainfall to the region Sunday afternoon through
  Monday. The greatest threat for flooding is across the Basin &
  Range and the eastern Sierra. Please see the Flash Flood Watch
  for additional details. Have multiple ways to receive alerts in
  case flood warnings are issued, and never drive through flooded
  roadways.

* Abundant cloud cover and rainfall will keep afternoon high
  temperatures 10 to 20 degrees below normal Sunday through
  Tuesday, with Monday likely being the chilliest day of the week.

* The center of what is left of Hilary will move through central
  Nevada on Monday. Across the Basin and Range, expect
  breezy/gusty conditions with gusts of 30-40 mph and locally
  higher inside any intense storm cores. If the track of Hilary
  shifts farther west, winds may become gustier for more of the
  region.

* Stay tuned to the National Hurricane Center by visiting
  www.hurricanes.gov for the latest on Hilary.

https://weather.gov/reno