Severe Thunderstorm Warning 16, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
145 PM PDT Sat Sep 2 2023

.SYNOPSIS...

Cool, unsettled weather will continue through Sunday with
widespread rainfall and scattered thunderstorms. Some storms may
become strong each afternoon through Sunday in the Basin and
Range. Warmer and much drier conditions will prevail Monday
onward.

&&

.DISCUSSION...

The calendar turned to meteorological fall and the atmosphere
certainly followed suit for the first day of September, featuring
fall-like temperatures, gloomy skies, and steady rain across the
Sierra and far western Nevada. 24-hour rainfall totals in the Tahoe
Basin generally varied from 0.20" to 0.75" with locally greater
totals over an inch. Meanwhile, the Greater Reno-Carson City-
Minden area received a few hundredths to a quarter inch.
Amazingly, Mt. Rose even had a fresh dusting of snow!

Latest radar observations reveal scattered showers across much of
the region with a few stronger cells in Mineral and Churchill
counties. Visible satellite depicts persistent clearing in cloud
coverage from Mineral to Pershing County, allowing for better
surface heating and subsequent instability (MUCAPE of 100-500 J/kg
per 19Z mesoanalysis). As such, areas generally east of US-95 and
south of I-80 will feature the best chance of afternoon
thunderstorms, possibly lasting into the early morning hours. A
few thunderstorms may become strong to marginally severe as semi-
discrete cells move into a favorable kinematic environment
characterized by effective bulk shear of 30-40 kts. Per CAMs,
timing of these stronger storms will favor the 2-6 PM timeframe
with potential hazards of small hail, gusty outflow winds up to 40
mph, heavy downpours and cloud-to-ground lightning.

The culprit behind the unsettled weather is a rather high-amplitude
trough and attendant closed low anchored near the northern
California coast. A "kicker" shortwave trough upstream will finally
dislodge the stronger trough, which will eject through the region
Sunday. Large scale ascent will overspread the Sierra and NE
California early Sunday morning before moving into western Nevada in
the afternoon. As a result, another north-to-south band of showers
and embedded thunderstorms will develop and provide widespread
rainfall through much of Sunday. This precipitation band will arrive
to the Sierra between 3-5 AM, moving into the Greater Reno-
Carson City-Minden area around 9-11 AM. Large scale ascent will
spatially align with areas east of US-95 duirng peak heating hours,
promoting scattered thunderstorms across Lyon, Mineral,
Churchill, and Pershing County during the afternoon. While the
strongest wind shear will be displaced well south and east of the
region, the western periphery of stronger mid-level flow will
briefly couple with the aforementioned counties in the early
afternoon. As such, more organized thunderstorms, capable of small
hail, strong outflows, and heavy downpours, will be possible
Sunday afternoon. Hi-Res ensembles seemingly favor the 12-4 PM
time frame for these storms in the Basin & Range, although timing
and location may change based on the upper trough progression. A
few showers may linger in the wake of the trough passage, but
convective activity should conclude in the early evening.

Temperatures will remain well below average this weekend with
Sunday being the coolest of the next 7 days. Highs will only reach
the 50s to low 60s for Sierra communities and upper 60s to low 70s
for lower western Nevada valleys. As skies clear, overnight lows
will flirt with/drop below the freezing mark Sunday and Monday
nights in Sierra valleys. Some fog/freezing fog will be possible
in the cold-prone valleys overnight Sunday and Monday, particularly
in the Martis Valley. For the remainder of the week, we will
slowly warm a couple degrees each day before arriving to seasonal
averages by next weekend. A couple of shortwaves will quickly
move through the region during the first half of the week, keeping
temperatures mild and maintaining a very slight (5-15%) chance of
showers and storms. However, consensus among ensembles favor a
warmer, drier solution throughout the upcoming week.

-Salas

&&

.AVIATION...

* A few showers and isolated thunderstorms (15-20%) for most
  terminals will continue into the evening. Expect mountain top
  obscurations for Sierra terminals due to lower ceilings and
  periods of MVFR conditions where moderate to heavier showers
  could reduce visibilities below 3-5 miles at times.

* A low pressure system moving into the Sierra and western NV will
  bring more widespread rain and a chance (10-20%) for an isolated
  storm or two overnight into Sunday morning. Storm chances
  (30-50%), however, increase later Sunday morning and afternoon
  across western NV with the potential near terminals east of
  US-95 in the Basin and Range for stronger T-storms capable of
  gusty outflows to 40-50 kts, heavy rainfall cores, and small
  hail.

* Showers and clouds will decrease overnight Sunday night allowing
  for increased radiational cooling over Sierra valleys. This will
  result in conditions favoring development of fog or freezing fog
  in Sierra valleys overnight into Monday morning. Drier and
  warmer conditions will spread into the region through the week
  and bring VFR conditions to area terminals. -Amanda

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&