Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 212036
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
136 PM PDT Sat Apr 21 2018

.SYNOPSIS...

Much warmer temperatures are expected through next week with mainly
dry conditions. A wave passing to the north on Sunday will bring
increased afternoon and evening winds. Low pressure developing
off the California coast will bring increasing chances for showers
and a few thunderstorms for mid to late next week.

&&

.SHORT TERM...

All showers and/or thunderstorms have been removed from the
forecast through Tuesday. Warm and dry conditions with clear to
partly cloudy skies are expected through the short term.

Sunday`s system has continued the drier trend, with partly cloudy
skies all that are expected in the Surprise Valley and far
northwest Nevada with deep forcing removed well to the north and
east. Elsewhere, west to northwest afternoon and evening breezes
are expected to kick up to between 20-30 mph as thermal gradients
intensify across the region in response to the weak trough moving
by to the north. This could be of some concern for small
watercraft on area lakes so check the forecast before heading out
on lakes Sunday afternoon or evening.

Monday, surface high pressure builds into the northern Great Basin
for a switch to light northeast-southeast lower level flow. This
flow will usher in a few degrees of cooling in the Basin/western
NV, with little change in the Sierra.

Tuesday, high pressure aloft shifts slightly eastward. Most
simulations have nothing more than hints at some cumulus development
for the afternoon and evening and model soundings look unsupportive
of more than shallow moist convection (cumulus). In support of
this idea, the 15Z SREF thunderstorm progs have fallen to a
minimal chance (5%) for thunderstorms in the Sierra near and just
south of Lake Tahoe. In past experiences, a SREF probability of
at least 20% has been indicative of thunderstorm development. All
that said, the GFS remains the outlier in bringing isolated
activity to the Sierra by early evening Tuesday. With probabilities
remaining very low (~10% or less) in most guidance, have removed
mention of showers and thunderstorms in the Sierra. -Snyder

.LONG TERM...Wednesday through next weekend...

The focus remains on the cut-off low for the extended period.
Higher confidence has developed this afternoon into Thursday with
the models remaining consistent in the low remaining offshore
with building instability. Temperatures will be the warmest of the
period with highs in the low 80s for western NV and near 70 for
Sierra valleys. The threat of convection will be there, especially
for the Sierra and adjacent lower valleys of western NV. The
Sweetwaters, Pine Nuts, and possibly central NV could also get
active for Thursday. Winds will generally be light with the south
flow aloft.

Friday into next weekend is where confidence goes from high to low,
and quite low at that. We do know the low will progress inland,
but how it does so greatly impacts the expected weather. The
latest GFS brings the low into southern Nevada by Sunday with
cooler temperatures and a good chance of showers and thunderstorms
each day from Friday through Sunday. The latest GEFS is in better
agreement with its operational run, but given it`s only 20
members, its lack of dispersion gives me pause.

The EC continues to take the low north into Oregon with showers
Friday, then drier southwest flow for the weekend. The 12Z EC is
further south and cooler than the 00Z run, but its ensemble shows
so many different ideas that it looks like spaghetti. Some support
the GFS, some the 00Z and 12Z EC, with a few taking it directly
over Reno-Tahoe.

Bottom line, the forecast will show the best chance of showers
Friday with lower chances for the weekend. We will also show a
cool down to near average. Keep in mind, it could be dry and warm
next weekend (EC) or cool and wet (GFS) and that the official
forecast is hitting the one in the middle, i.e., this forecast
gives us maximum flexibility but has little chance of verifying.
X

&&

.AVIATION...

Widespread VFR conditions through the rest of the weekend outside
of a 30-40% chance for early morning fog around KTRK. Sunday, a
weak upper trough moving over and north of the NV/OR/ID border
will enhance west-northwest breezes, with gusts up to 20-25 kts
after 2 PM (21Z). -Snyder

&&

.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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