Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 280844

Area Forecast Discussion
National Weather Service Reno NV
144 AM PDT Sun May 28 2023

...Unsettled weather will continue high chances for daily
thunderstorms through at least mid-week...


Daily showers and thunderstorms (up to 70% chance) are forecast
through Memorial Day and into the middle of the week. Lower storm
chances arrive by Thursday and into next weekend. Stronger storms
may produce locally heavy rainfall, small hail, gusty outflow
winds, and frequent lightning. Snowmelt will keep streams running
cold and fast, with main flood concerns for the Walker River.


.SHORT TERM (Through Monday Night)...

The active weather pattern will continue through the short term
(and longer) as a cutoff low drops into northwest California
which will provide the forcing mechanism to fire off daily
showers and thunderstorms. Temperatures will remain seasonable,
with mid 70s to around 80 in western Nevada valleys and 60s in the
Sierra. So, let`s talk about the convection since the primary
threats will differ a bit between Sunday and Monday:

* SUNDAY...Unlike Saturday where most of the convection was along
  and north of I-80, the low will be dropping farther south and
  shifting the dynamics southward along with it. Southwesterly
  0-6 km bulk shear vectors of 25-35 kt will favor storm motion
  towards the northeast initially, before taking a northward
  motion by late afternoon as the low sinks south of our latitude.
  The added shear, combined with 300-600 J/kg MLCAPE will allow
  for a few organized/sustained updrafts capable of producing some
  hail. 00Z HREF guidance highlights S Lyon/Mineral/E Churchill
  for these stronger storms by painting a 10-20% chance of max
  updraft helicity greater than 25 m^2/s^2. However, the greatest
  probabilities remain east of our area over Lander/Eureka
  counties. One thing to note is that while PWATs are high,
  relatively speaking, there will be more moisture trapped in the
  lower levels today which will dampen outflow winds. In summary,
  we`ll see quicker storm motions today equating to a lower flash
  flood threat (but terrain driven training of storms may still
  cause issues), stronger updrafts leading to a greater hail
  threat, and lower chance of seeing strong downburst winds.

* MONDAY...Memorial Day will see another day of active weather.
  Much weaker flow is anticipated, which will lead to storms being
  more pulse-like. Forecast soundings suggest higher based storms
  this day, which checks out as DCAPE looks to be much higher
  over the Basin & Range compared to Sunday. So expect collapsing
  storms to be capable of producing strong outflow wind gusts.
  Moisture and instability will be plentiful (up to 900 J/kg
  MLCAPE) and with the slower storm motion, we`ll have a higher
  threat of flash flooding as blended model guidance places the
  highest rain chances (50%-70%) over eastern Sierra/Tahoe
  Basin/northeast California where low-level convergence will be
  maximized in the weak flow. The 00Z HREF`s probability of
  exceeding 1 hour flash flood guidance highlights much of the
  Sierra. This happens to also be where many of our problematic
  burn scars are. Opted to introduce heavy rain wording into the
  forecast for Monday afternoon/evening. Just be careful if you`ll
  be near any flashy small creaks or streams - and have an escape
  plan to get to higher ground if necessary.


.LONG TERM...Tuesday through next weekend...

Scattered to numerous showers and thunderstorms continue
through midweek--even as the weekend low slowly departs across
the southwest US, additional upper disturbances are ready to
fill that void, provide some forcing in the pre-existing
moist and unstable air mass. Wednesday could see more organized
convection with a few stronger cells, as a trough passage across
the northwest US brings larger scale lift into eastern CA-
western NV during the afternoon-evening.

Later in the week, the thunderstorm threat continues, although at
this time coverage appears to decrease with more isolated activity
generally favoring the eastern Sierra by Friday and Saturday,
along with slight warming into the lower 80s for western NV
valleys/near 70 for Sierra communities. The location of smaller
scale shortwaves or upper disturbances varies more in the medium
range ensemble guidance, leading to reduced confidence in the
thunderstorm chances. Coverage could increase again by later next
weekend with a more potent low pressure approaching the west
coast, with this system potentially meandering around the western
US and keeping daily shower/thunder chances going through the
first week of June. MJD



A steady pattern of scattered afternoon showers and thunderstorms
will continue for the next few days, mainly between 20-02Z. The
greatest coverage at the main terminals is currently favored for
Monday-Tuesday, with storms bringing the potential for short
periods of MVFR/IFR conditions from heavy rainfall, small hail,
erratic wind gusts of 30+ kt and frequent lightning.

Outside of storms, conditions will be VFR with scattered to broken
cumulus decks. Periods of fog will be possible each night at KTRK
from 10-15z, especially after days where rain occurs at the
airport. MJD



No significant updates or changes in ongoing flood concerns.
Headwater flows have diminished a bit with cooler temperatures,
and crests are slowly migrating down mainstem rivers.

* WALKER: Prolonged minor to moderate flooding will continue along
  the East Fork and main-stem of the Walker River. The Walker
  River in the Mason Valley continues to trend slightly downward.
  Very minimal decreases in flow are expected this weekend, but it
  will depend on reservoir management adjustments which are
  intended to maintain storage and to mitigate future (and
  potentially higher) peaks.

* CARSON: Some minor impacts may continue along the East and West
  Forks of the Carson, but trends continue to be more favorable
  and lower than they were earlier in the week.

* MONO COUNTY: Keep a close eye on Mono county small streams which
  have been running very high. Thunderstorm activity will have the
  greatest chance to impact these smaller basins.

* THUNDERSTORMS: Thunderstorms will continue to be a wild card.
  Unsettled storm pattern continues through Memorial Day (and
  beyond). With saturated soils and elevated streamflows,
  additional rain will result in rapid rises and enhanced flooding
  potential. Slower storm motion is expected on Monday which will
  enhance the flood threat. These storms will be most impactful
  along smaller creeks and streams, but could also exacerbate
  problems along mainstem rivers which are already flooding or are
  very close to flood impact levels. Note: River forecasts are
  incapable of incorporating these short duration high intensity
  rain events.



.REV Watches/Warnings/Advisories...

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