Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 092001

Area Forecast Discussion
National Weather Service Reno NV
101 PM PDT Fri Jun 9 2023


Thunderstorm chances decrease today, with greater coverage
anticipated Saturday through Monday. Storms may bring heavy rain
and flash flood concerns, along with gusty and erratic winds,
small hail, and plenty of lightning. Temperatures will hold steady
in the near or slightly below normal range. While storm chances
decrease next week, there are no signs of fully drying out.



The persistent omega blocking pattern consisting of low pressure
anchored off the SoCal coast will continue into early next week.
This pattern will continue to provide anomalously high
instability and moisture availability across our region. As such,
atmospheric conditions remain favorable for daily afternoon
shower and thunderstorm development for the foreseeable future.

Today, a weakening area of low pressure over SoCal will lift
across our region and provide forcing for yet another round of
afternoon shower and thunderstorm development. Coverage will be
more isolated and pulse-like today, with high CAPE values (well
above the 90th percentile of climatology), but little in the way
of shear to sustain updrafts. The exception of this includes areas
near the Oregon border, where main forcing accompanying the
shortwave will lead to more organized storms and an increased
threat for heavy rainfall.

After the aforementioned low exits the region today, another closed
low will quickly take its place along the SoCal coast. Thunderstorm
chances greatly increase Saturday through Monday as the low slowly
rotates inland, further enhancing moist, southerly flow and
increasing divergence aloft over the region. The ECMWF EFI
highlights anomalous CAPE, CAPE-Shear, and QPF each day across the
region, indicating these storms will be more organized and
widespread. Model soundings this weekend also corroborate this
potential, with CAPE values upwards of 1000-1200 J/kg, effective
bulk shear near 30 kts, steep mid-level lapse rates, and DCAPE
upwards of 1000 J/kg. As such, the thermodynamic ingredients are all
there for heavy rainfall, frequent lightning, gusty and erratic
outflow winds exceeding 50 mph, and small hail. Flash flooding will
also be a concern due to the widespread nature of storms. If plans
take you outdoors this weekend, have a way to receive weather alerts
and have a safety plan in the case that storms threaten your area.

A ridge over the north Pacific begins to strengthen on Tuesday,
nudging the main low eastward and leaving behind a weaker area of
low pressure off the SoCal coast. This ridge doesn`t look to have
much of an impact on our active pattern in the long-term however,
with the area of low pressure providing additional moisture
availability to keep storm activity going, perhaps through the end
of next week. Comparatively, storm chances will be lower next week
from Tuesday onward, with a 15-25% chance of thunder areawide each
afternoon. Temperatures will also moderate back to seasonal
averages, with highs in the mid-80s across western Nevada and the
low 70s for Sierra valleys. -Whitlam



* Thunderstorms appear a bit weaker today so far with generally
  isolated, shallow storms. Coverage will be also be less this
  afternoon with the highest chances (60%) near the Oregon border
  and 15-35% chances elsewhere. For KTRK/KTVL/KRNO/KCXP/KMEV through
  00z, thunderstorm potential will be around 10-20% chances. For
  KMMH/KNFL/KLOL/KHTH through 02z, there will be a 35% chance.

* Any storms may produce terrain obscuration and intermittent
  lowering of CIGS/VIS, along with isolated areas of blowing dust
  with erratic thunderstorm outflow winds.

* WEEKEND: Plan on widespread showers and thunderstorms Saturday
  through Monday, with an increased potential for MVFR-IFR
  conditions and heavy rain. There will be a 50-80% chance for a
  storm at any given location each afternoon and evening, with
  spotty showers persisting overnight.

* Aside from thunderstorms, there are still chances for shallow,
  patchy fog in the Martis Valley, including KTRK, from
  approximately 10z-15z each morning. antecedent rainfall and
  clearing overnight will increase the likelihood of fog




* Flash flooding is a primary concern with potential for heavy rain
  and slow moving storms, especially Saturday through Monday.
  Areas that are particularly prone are recent burn areas and
  creeks and streams already near bankfull with ongoing snowmelt,
  but flash flooding may not be limited to these areas.

* Cloud cover and cooler temperatures will continue to moderate
  snowmelt, but will be counter-balanced by areas of heavy rain
  and periods of intermittent sun to keep the hydrologic response
  a forecasting challenge. Flows along the West Walker River are
  expected to remain high, but below flood stage, while fairly
  steady flood flows are expected along the East Walker.

* Moderate flooding continues along the Walker near Mason, but the
  level has dropped nearly a half foot since the recent crest late
  Wednesday night, and is expected to stay fairly level through
  the weekend. Downstream at Wabuska, the river is currently
  cresting and this crest will take a day or two to reach Weber
  Reservoir. Keep an eye out for heavy rain from thunderstorms
  that are not well accounted for in the hydrologic modeling and
  could lead to unexpected rises, especially storms feeding the
  forks of the Walker below Topaz and Bridgeport reservoirs.
  Additional future rises along the Walker are likely with
  prolonged flooding expected to last into July. As an example, in
  1995, the West Walker below Little Walker peaked on July 9th,
  and Wabuska peaked on July 14th!

* High flows to continue along the west fork of the Carson, but
  the current forecast keeps the rivers below flood stage. Minor
  flooding is ongoing along the lower Humboldt at Imlay with a few
  inches of water flowing over Tungsten Road. Flows at Imlay are
  expected to rise slightly into next week, remain in minor flood
  stage, before very slowly receding. The lower Humboldt is
  unlikely to return to peak again, with snow limited to only the
  highest terrain.

* Creeks and streams areawide will continue to run high, cold, and
  fast; with some potentially out of banks especially throughout
  portions of Mono County. As a result, banks may be unstable and
  any debris can send flows into unexpected areas, so take caution
  near waterway edges.

* The wild card will continue to be thunderstorm chances and
  coverage, with storms in the forecast today through at least the
  early part of next week. All signs are pointing toward the
  potential for thunderstorms Saturday through Monday to be able
  to produce heavy rainfall. Cooler temps along with cloud
  coverage from thunderstorms will help slow the diurnally driven



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