Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 202137
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
237 PM PDT Sat Apr 20 2019

.SYNOPSIS...

An area of low pressure will bring cooler and breezy conditions
this weekend with a chance for showers and isolated thunderstorms.
Drier and warmer conditions are expected next week. The warmer
temperatures will lead to increases in cold and swift water in
area streams.

&&

.SHORT TERM...

Minor changes to the short term this forecast cycle regarding
thunderstorm development for this afternoon/early evening and winds
for Sunday afternoon.

The cloud cover and southwest winds have increased region wide this
afternoon due to the presence of a low pressure trough that is
currently moving through the west coast. Gusts of 25-35 mph are
anticipated for the rest of today with the Sierra ridges around 70
mph before decreasing and becoming northwest overnight.

Taking a look at the current radar, light rain showers with embedded
thunderstorms are impacting portions of Mono, Pershing, Churchill,
and northern Lassen counties. Short range model guidance does
continue this shower activity through the evening hours with less of
a chance towards the south (Mono County) but higher for areas north
of I-80 where unstable atmospheric conditions persist. Thunderstorm
coverage will be on the low end due to the increased cloud cover
inhibiting daytime heating. Nonetheless, any storms that do form
can bring small hail, rain, and erratic outflow gusts of 35 mph.
Expect thunderstorm development to cease by nightfall due to the
lack of differential heating.

As the trough makes its way through western Nevada tonight into
Sunday, shower activity will be more focused along the Sierra
crest in Mono County due to upslope flow as well as for areas east
of US- 95 on the backside of the low pressure trough. By Sunday
afternoon, north-northwest winds behind the trough will be brisk
with gusts of 25-35 mph, possibly higher for Washoe, Pershing, and
Churchill counties. We have issued a Lake Wind Advisory for
Pyramid Lake during this time ending by Sunday evening due to the
potential for gusty north winds. Daytime temperatures will also
remain cooler than what we have experienced this past week. Highs
are expected to be in the low to mid 60s for the western Nevada
valleys with the Sierra being about 10 degrees cooler.

As we start the new work week, winds decrease and temperatures
recover reaching into the mid to upper 70s range by Tuesday as a
ridge of high pressure begins to build over the west coast bringing
tranquil weather conditions for much of the week.

-LaGuardia



.LONG TERM...Wednesday through Saturday...

The only substantive changes made to the forecast this cycle were to
increase winds slightly for both Thursday and Friday. Model
simulations continue to trend in better alignment with the overall
broad scale pattern...but there remain some details that differ.

A flat ridge over the region Wednesday begins to slide east late
Thursday. The operational GFS is still trying to develop some
convection along the Sierra and in far northeast California
Wednesday...but the GFS is known to over do convection driven by
mainly daytime heating early in the season. The ECMWF and most
ensembles do not really agree with this so we have left out
mention of showers for now.

The earlier trend of slowing the entrance of the trough Thursday and
Friday is continuing. The deterministic solutions do still indicate
some small chances of convection Thursday...but the better chances
are Friday as instability and forcing increase with the main trough.
That means at least a slight chance of thunderstorms Friday as well.

Surface winds Thursday were increased a bit as a better thermal
gradient develops between the Sierra and the basin and range. The
slower entrance of the trough should allow highs in the lower
valleys to reach the lower to mid 80s. This will drive stronger
afternoon winds in an almost zephyr-like pattern. Winds increase
even more for Friday as upper level winds increase and the surface
pressure gradient increases ahead of the trough. We may not quite
get to advisory criteria Friday...but winds will be quite gusty east
of the Sierra.

Warming temperatures most of the week will also drive increased
snowmelt with rivers and streams likely running higher by the end of
next week when compared to the last couple of days.

By Saturday zonal flow returns as the trough slides east. High
temperatures should be about 6-10 degrees cooler and clouds will
linger...but precipitation chances will be minimal.


&&

.AVIATION...

Scattered showers have developed over the northern 2/3rds of the
forecast area this afternoon...with a few isolated thunderstorms.
Occasional MVFR/IFR conditions are likely in the heavier showers
through the early evening hours along with turbulence in and near
the showers and thunderstorms. Gusty low level gradient winds have
also developed over much of the area...but the gusts are not much
more than 20-25 kts; stronger gusts are likely near the heavier
showers. So...mechanical turbulence is also possible...especially
along and just east of the Sierra as ridge winds are still gusting
to 50-60 kts.

Showers linger into Sunday morning east of Highway 95 before
clearing develops. There may be a few upslope showers south of
Bridgeport Sunday.

A ridge starts to build in and that will produce gusty easterly
winds over the Sierra Sunday night and Monday night. The western
slopes may see some turbulence in response to these winds.

Otherwise...VFR conditions return for much of the area starting late
Sunday into the middle of next before the next shortwave trough
brings a renewed chance for showers and thunderstorms.

&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory until 8 PM PDT this evening for Pyramid Lake
     in NVZ004.

     Lake Wind Advisory from noon to 8 PM PDT Sunday for Pyramid Lake
     in NVZ004.

     Lake Wind Advisory until 6 PM PDT this evening for Lake Tahoe in
     NVZ002.

CA...Lake Wind Advisory until 6 PM PDT this evening for Lake Tahoe in
     CAZ072.

&&

$$

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


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