Flash Flood Warning 4, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
124 PM PDT Wed Aug 3 2022

.SYNOPSIS...

Persistent monsoonal flow will continue to generate showers and
thunderstorms each afternoon and evening through at least Saturday.
Storms will be capable of producing heavy rain, flash flooding,
frequent lightning, small hail, and gusty outflow winds with
blowing dust. Temperatures will cool to around average this
weekend. Cloud cover could help to dampen daytime highs across
western Nevada.

&&

.SHORT TERM...Through Thursday night...

This forecaster had a few rumbles of thunder and a wetting rain at
his house last night, which was a welcome smell of petrichor. After
quite a humid and clear morning, showers and thunderstorms are
beginning to build along the higher terrain across northeast
California, the Sierra Front, and the Eastern Sierra.

Thunderstorms Today and Thursday:

* Thunderstorms will be possible this afternoon and evening across
  northeast California, northwest Nevada, along the Interstate 80
  corridor, as well as the eastern Sierra from the Tahoe Basin south
  into Mono County. As mentioned previously, the stronger storms
  will be most likely south of US Highway 50. The main hazards will
  be frequent lightning, localized heavy rainfall, small hail, and
  gusty outflow winds to 45 mph. Blowing dust may also be possible
  ahead of outflow boundaries in areas that have not received
  rainfall recently.

* A Flash Flood Watch is in effect from noon this afternoon through
  9 PM PDT Thursday for areas mainly south of US Highway 50. You
  might be asking yourself: why the Flash Flood Watch issuance?
  Well, this morning's 12z sounding from our office showed a very
  deep and moist vertical profile, coupled with CAPE near 1000 J/kg,
  a low LCL for this area's standards, a record high PWAT of 1.07"
  (the previous record for 8/3 was 1.01"), and slow storm-relative
  wind speeds, which should promote the training of thunderstorms
  over burn scars and steep terrain. Nearly all CAMs are indicating
  heavy convective rainfall possible across much of Douglas, Alpine,
  southern Lyon, Mono, and Mineral counties between 3:00 PM and 9:00
  PM PDT today and Thursday. This excessive rainfall could trigger
  flash flooding of low-lying areas and debris flows in and near
  recent burn scars. Residents and those recreating in and
  immediately next to recent burn scars should prepare for potential
  flooding impacts. Be ready to act and move to higher ground should
  a Flash Flood Warning be issued for your location.

* Thursday will nearly be a repeat of this afternoon and evening,
  with most of the action located south of Interstate 80. Once
  again, we'll see chances for heavy rainfall south of US 50, with
  recent burn scars and steep terrain being the most dangerous areas
  to be near. In addition to heavy rainfall, frequent lightning,
  small hail, and gusty outflow winds to 50 mph can be expected.

Winds and Temperatures:

* Winds outside of thunderstorms will be pretty tame this afternoon
  and Thursday afternoon, with gusts to 25 mph expected from the
  west. Near thunderstorms, erratic wind gusts as high as 50 mph can
  be expected.

* High temperatures this afternoon look to be a little warmer
  compared to tomorrow, due to the chance for more cloud cover from
  convective debris. Highs are expected to climb into the mid-to-
  upper 90s this afternoon across western Nevada and northeast
  California, and in the 80s across Sierra valleys. Thursday, highs
  will struggle to reach the low-90s across the lower valleys and
  low-80s in Sierra valleys.

Smoke/Air Quality:

* Haze and degraded air quality are also expected across northeast
  California today and tomorrow due to ongoing fire activity in
  northern California.

-Johnston

.LONG TERM...Friday onward...

Shower and thunderstorm chances will continue for most of the region
on Friday as high pressure remains settled over the Four Corners
region. Moisture will continue to flow around the western periphery
of the high, keeping PWATs in the 0.8-1.1" range Friday. These
values indicate potential for storms to produce heavy rains that
could lead to flash flooding in sensitive terrain such as burn areas
or steep slopes. However, given that we are on a stretch of
monsoonal flow, it is possible skies may not clear out Friday
morning and consequently limit surface heating. Under this scenario,
the lack of surface heating will inhibit destabilization of the
atmosphere, and in turn eliminate significant thunderstorm activity.

A shortwave trough is expected to brush by to our north on Saturday,
subsequently flattening the ridge and directing dry southwest flow
over our region. Southwest flow will close the door to any
additional monsoonal moisture pushes, but thunderstorm chances
continue through Saturday. Greatest thunderstorm activity will
likely remain confined to areas farther south, especially in
Mono/Mineral counties. Any storms that develop may likely produce
gusty and erratic winds as model soundings suggest dry lower-levels
and high DCAPE.

Ensemble guidance currently suggests that as the trough exits the
region on Saturday, a closed low currently sitting off the NorCal
coast will begin to lift to the northeast into the Pacific NW on
Sunday, allowing dry southwest flow to continue through the end of
the forecast period. This pattern will likely keep thunderstorm
chances slight through mid-week. -Whitlam

&&

.AVIATION...

* Showers and thunderstorms are beginning to form this afternoon
  across much of the area. These showers and storms will mainly
  affect terminal sites south of Interstate 80 and last through
  approximately 06z Thursday. Tomorrow we'll see nearly the same
  situation.

* Near and within thunderstorms, expect localized heavy rainfall,
  wet microbursts with erratic and gusty outflow winds to 40 kts,
  low-level wind shear, small hail, frequent lightning, and terrain
  obscurations. Stronger outflow winds tracking over dry desert
  ground may also loft dust, which may reduce ground and slantwise
  visibility also.

* Thunderstorm chances remain through the weekend, although coverage
  looks to lessen each day past Friday.

-Johnston

&&

.REV Watches/Warnings/Advisories...
NV...Flood Watch through Thursday evening NVZ001>003.

CA...Flood Watch through Thursday evening CAZ072-073.

&&

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RENO NV
416 PM PDT WED AUG 3 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0407 PM     DEBRIS FLOW      GROVER HOT SPRINGS      38.70N 119.84W
08/03/2022                   ALPINE             CA   PARK/FOREST SRVC

            GROVER HOT SPRINGS STATE PARK STAFF REPORTED
            DEBRIS FLOW OVER HOT SPRINGS RD DUE TO
            INTENSE, HEAVY RAINFALL. DEPTH AND DAMAGE
            UNKNOWN AT THIS TIME.

0411 PM     DEBRIS FLOW      1 ENE GROVER HOT SPRING 38.70N 119.83W
08/03/2022                   ALPINE             CA   DEPT OF HIGHWAYS

            CALTRANS AND CHP REPORTING BOULDERS AND
            ROCKS IN THE AREA. ONE PART OF HOT SPRINGS
            RD STARTING TO WASH OUT. ONE IS IMPASSIBLE.

0409 PM     HAIL             GROVER HOT SPRINGS      38.70N 119.84W
08/03/2022  E0.25 INCH       ALPINE             CA   PARK/FOREST SRVC

            GROVER HOT SPRINGS STAFF REPORTED 0.25 INCH
            HAIL.

&&

WHITLAM