Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 290954

Area Forecast Discussion
National Weather Service Reno NV
254 AM PDT Mon May 29 2023


Scattered to numerous showers and thunderstorms are expected again
today and Tuesday, with slower storm motions increasing the risk
for heavy rainfall producing flash flooding. The potential for
storms decreases by mid to late week, but won`t completely
disappear. Snowmelt flood concerns will also continue for the
Walker River basin area.


.SHORT TERM (Through Tuesday Night)...

Main changes for the short term are extending the flood watch
through Tuesday evening, and adding Mineral-southern Lyon
counties to the watch.

A slow moving low pressure near the central CA coast will drift
inland across far southern CA on Tuesday. A broad area of upper
level forcing/divergence associated with this low will remain
present over the eastern Sierra and parts of western NV for both
days. This will combine with a moist and unstable air mass to
produce scattered-numerous showers and thunderstorms. Steering
flow will be weaker compared to recent days, leading to slower
cell motion and longer duration of heavier rainfall where storms
occur. Given the most likely track of the upper low, storm
development is projected to begin near the Sierra around midday
today and again Tuesday, then expand into the remainder of eastern
CA and much of western NV during each afternoon and evening. Surface
convergence from storm outflows and terrain features will be the
primary mechanisms for sustaining convection, with cells more
likely to develop overhead rather than move in from another
location. For those with outdoor recreation plans for the
remainder of the holiday weekend (and on Tuesday), this manner of
storm development could bring adverse conditions more abruptly, so
ensure quick access to shelter.

Lighter shower activity will linger through the late evening and
overnight hours, mainly in parts of northwest-west central NV.
Widespread cloud cover will keep high and low temperatures in
similar ranges as recent days. MJD

.LONG TERM (Wednesday to Next Monday)...

Wednesday will bring sunny, rain-free skies to all of western
Nevada and northeast California... Just kidding! :-)

While the upper level low will finally begin to migrate eastward
towards southern Nevada and northwest Arizona, abundant moisture
(PWATs 0.6-0.8 inches) will linger over the area on Wednesday. NAM
surface based CAPE and low-level convergence signals appear more
than enough to fire off convection despite not much in the way of
large scale forcing. We won`t see quick storm movement on this day
either, so there will still be a flash flood threat with perhaps
a higher emphasis on the eastern Sierra. Afternoon cloud cover and
lack of ridging will keep temps near or a little below normal for
the end of May.

Until we scour out the moisture in our area, daily shower and
thunderstorm chances will persist. This reduction of moisture and
resultant lower rain chances appears to be the case later in the
work week, at least temporarily:

* Thursday PWATs are lowered, particularly over the Sierra. A
  progressive shortwave will assist in firing off convection, but
  timing and how far south the shortwave gets will play a role in
  thunderstorm coverage. Right now, scattered chances (25-40%)
  exist but wouldn`t be surprised to see these lower some,
  especially over CA.

* Brief ridging looks to take hold on Friday. This will help to
  suppress shower and thunderstorm coverage. Blended guidance
  supports this with only a 5-15% chance of rain.

* Anticyclonic flow sets up to our east and another cutoff low
  moves towards southwest California as we head into next weekend.
  These two features will aid each other in advecting monsoonal
  moisture into western Nevada. As a result, showers and
  thunderstorms will return to the picture each day to begin the
  first week of June. Gradual warming will also occur with 80s in
  western Nevada and 70s in the Sierra.




Favorable setup for convection to impact our airport terminals
this afternoon and evening. Initiation should begin around 21Z,
and taper off and/or move north of I-80 by 04-06Z. For
RNO/CXP/MEV, thunderstorm chances are 60-70% while TRK and TVL are
near 80% and MMH is closer to 50%. Strong outflow winds, small
hail, and brief periods of MVFR/IFR cigs/vsbys will be possible.
Expect a very similar situation Tuesday afternoon and evening.

With the added low-level moisture, TRK may experience fog late
overnight into early morning hours each day. Cloud cover during
this time will be the variable as to whether it develops or not.




UPDATE: Flood Watch extended through Tuesday evening. Slow-
moving thunderstorms will produce areas of heavy rainfall. High
threat areas include: Much of the Sierra, especially burn scars,
steep canyons, and along rivers and creeks.

* WALKER: Prolonged moderate flooding will continue along the
  East Fork and mainstem Walker River. Flows highly dependent upon
  on reservoir management adjustments which are intended to
  maintain storage and to mitigate future (and potentially higher)

* CARSON: Similar diurnal flows will continue for the next few
  days along the East and West Forks of the Carson with crests at
  Woodfords just below minor flood stage, but no new flood impacts
  are expected from snowmelt alone.

* MONO COUNTY: Keep a close eye on Mono county small streams which
  have been running very high. Heavy rainfall with thunderstorms,
  especially today and Tuesday, will have the greatest chance to
  impact these smaller basins.

* THUNDERSTORMS: Unsettled storm pattern continues this week. With
  saturated soils and elevated streamflows, additional rain from
  slow moving thunderstorms today and Tuesday could lead to rapid
  rises and enhanced flooding potential. These storms will be
  most impactful along smaller creeks and streams, but could also
  exacerbate problems along mainstem rivers are already at or
  close to flood impact levels. Remember that the river forecasts
  do not account for these small scale/short duration heavier rain



.REV Watches/Warnings/Advisories...
NV...Flood Watch from 1 PM PDT this afternoon through Tuesday evening

CA...Flood Watch from 1 PM PDT this afternoon through Tuesday evening


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