Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 220913
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
213 AM PDT Tue May 22 2018

.SYNOPSIS...

Low pressure systems will continue to affect the Sierra and western
Nevada this week and into at least the first part of the Memorial
Day weekend. Locally heavy rain, small hail and gusty winds will
accompany stronger storms. Temperatures will remain seasonally
mild for late May.

&&

.SHORT TERM...

Upper low centered over southern NV will lift slowly northward
today and weaken, then exit to the northeast tonight and
Wednesday. A bit more north flow across western NV on the back
side of upper low will limit coverage across much of western NV
from I-80 southward with the best chances for storms in the
deformation across northern Lassen County into far northwest NV as
well as right along the Sierra. For the Sierra however, a north to
northeast steering flow would suggest best storms will be west of
the crest. We maintained scattered coverage overall, but lowered
the lightning potential across western NV. For Wednesday, a
general south to southwest flow returns as the next trough in the
Pacific approaches. This will increase convergence along the
Highway 395 corridor, especially from Reno-Carson City northward
as westerlies pick up. Storms that develop along the Sierra will
tend to push off the crest and intensify as they encounter
increasing convergence with a few strong storms likely.

By Thursday, a rather dynamic upper low will approach with
increasing mid level winds and upper level divergence. This will
result in thunderstorm chances increasing again with best coverage
from the Tahoe Basin northward into northeast CA and northwest
NV. Temperatures will be seasonal with mid 60s Sierra and mid 70s
to around 80 degrees across lower elevations. Hohmann

.LONG TERM...Friday through Monday...

The overall reasoning during the extended portion of the forecast
has changed very little...but there were changes made to the
forecast POPS and temperatures for Friday and Saturday. The
deterministic models have come into much better agreement and many
of the GEFS ensemble members are in line as well...increasing the
confidence in the forecast even this far out.

The forecast models are converging on a solution that brings the
next upper low into the region Friday and stalls it over the
forecast area Saturday. The models are also showing increasing jet
dynamics Friday that should boost instability and the prospect for
stronger thunderstorms and more widespread showers...especially over
the northern half of the forecast region. Increasing the POPs may
also mean an earlier start and likely lower high temperatures.

Saturday looks to be cool and wet with even more widespread showers.
The thunderstorm prospects may not be quite as good Saturday given
more cloud cover and decreased low level instability as high
temperatures lower...but the presence of the upper low is likely to
make this the wettest day of the holiday weekend. The cold upper
low could drop snow levels to less than 8000 ft at times...likely
producing accumulating snows at the highest elevations and over
the passes above 7500 feet.

The low looks to slowly move east Sunday...but may not move out fast
enough to end convection. We have left slight chance POPs in the
eastern and northern parts of the forecast area Sunday...but since
the low level moisture will not be scoured out...it is possible that
convection will develop near the mountain ranges in the western part
of the forecast area later in the day due to differential heating.

Monday looks like the driest day of the weekend with temperatures
rebounding to normal. While we do not explicitly mention convection
for Monday...it is not out of the realm of possibility that there
could be some showers along the mountain ranges late in the day.

&&

.AVIATION...

The presence of a weakening upper level low pressure area will lead
to showers and thunderstorms again today over the forecast area.
Coverage is likely to be less than Monday with the best chances near
the Sierra...over northeast California...and in the eastern part of
the basin and range country. All of the attendant issues with
thunderstorms are likely: gusty surface winds...turbulence...small
hail. Patchy fog will produce MVFR to IFR conditions for KTRK and
KTVL this morning and MVFR conditions are possible near
thunderstorms today. But otherwise...VFR conditions are likely most
areas.

Showers and thunderstorms develop again Wednesday and Thursday as
the area remains relatively moist ahead of yet another area of
low pressure approaching the west coast. Showers and thunderstorms
increase in coverage Friday and Saturday as that upper level low
moves inland and becomes entrenched by Saturday.

&&

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

$$

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


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