Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 232141
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
241 PM PDT Sun Apr 23 2017

.SYNOPSIS...

Several weak systems passing through the region throughout the
work week will bring chances for light showers in addition to
breezy winds. Temperatures will fall to slightly below average
this week with drier and warmer conditions looking more likely
for next weekend.

&&

.SHORT TERM...Through Wednesday Night...

Several weak systems will brush through the region over the next few
days bringing period of breezy winds, cooler temperatures, and light
showers.

Breezy winds this afternoon will weaken overnight in valley
locations, but strengthen across ridgelines as a the jet stream
moves across northern California into Nevada. The strongest 700 mb
winds remain off the CA coastline Monday, with wind speeds across
the Sierra in the 35-45 kt range. This is likely to lead to ridge
gusts peaking 75-90 mph with mountain wave activity possible for
aviation. Valley winds will increase through the day as well as the
surface gradient increases and winds mix down to the surface.
Surface wind gusts of 30 to 45 mph are possible across much of the
eastern Sierra and western Nevada Monday bringing choppy lake
conditions. A Lake Wind Advisory has been issued for Pyramid Lake
and Lake Tahoe on Monday to account for this. Another round of gusty
winds is looking likely for Wednesday.

As far as timing, the first in the series of the 3 waves arrives
tonight into Monday with a definitive break now showing up behind it
on Tuesday morning. The warm air advection driven wave on Tuesday
will keep low end precipitation chances near the Oregon border,
followed by the third, slightly stronger, wave Wednesday. The main
period of concern for snow on Sierra passes is Monday night into
Tuesday morning, however this also coincides with the system
exiting. Therefore, very light snow remains possible, but impacts
should be short-lived.

The  trajectory of the jet stream and position of the main area of
low pressure well to the north will lead to the best precipitation
chances north of I-80 Monday through Wednesday. These waves are
fairly progressive and lack organization this far south, so
precipitation totals should be minimal. Generally a couple tenths up
to a third of an inch is possible for the Sierra and northeast
California with one to two tenths in the Tahoe Basin over the next 3
days. The Warner Mountains near the Oregon border may see up to a
half inch. Western Nevada remains largely shadowed, though better
precipitation chances exist from central Nevada eastward due to
better jet dynamics. Farther south into Mono and Mineral Counties,
some sprinkles are possible, but many locations will stay dry. -Dawn


.LONG TERM...Thursday through Sunday.

Another cold front is expected to move through the Great Basin
Thursday into Friday on the back side of the exiting trough. This
cold front is digging in farther west along the Sierra then previous
model simulations, so raised ridge winds and cooled temperatures
on Friday. With the cold pool now banking up against the east side
of the Sierra this will keep breezy northwest winds in the
forecast Thursday and leave the possibility open of some light
showers on Friday.

As we go into the weekend the deep trough over the Great Basin will
begin to move into the four corners region. This will allow the
ridge in the eastern Pacific to move closer to the west coast.
However for the weekend, the deep trough over the Rockies will keep
the ridge axis from moving over the west coast and the continued
storm track into the Pacific Northwest will keep the ridge from
becoming as amplified as earlier model simulations suggested.

The weekend still looks like it is going to be precipitation free
with near average temperatures. Warm 700 mb temps will start to
push into the region over the weekend with above freezing
overnight temperature at upper elevations becoming increasingly
likely towards the end of the weekend. As happened this weekend
the storm track could come a little more south then currently
forecast, most likely though, this would only create a period of
increased winds and clouds for the weekend. -Zach


.Week 2 Outlook...May 1st-7th...Issued 3pm 4/23...

A ridge of high pressure, or upside down trough, is again forecast
for the far eastern Pacific during the first week of May. There is
still relatively high uncertainty on whether, or at least when, the
ridge axis will be able to progress over the western U.S. and
bring well above average temperatures to the region. Model
simulations during this very active winter and spring have been
over predicting ridging along the west coast. With the ridge
building in the far eastern Pacific shortwaves will continue to be
able to dig into the Great Basin keeping the ridge axis out to
sea. This may keep the ridge from amplifying significantly over
the west coast until near the end of, or past, the 2 week time
period.

With the ridge continuing to strengthen in the eastern Pacific,
confidence is relatively high (for a week 2 outlook) that we won`t
see any strong atmospheric river induced storms for the beginning of
May. Fast moving cold fronts dropping in from the north with periods
of light precipitation will remain possible as long as the ridge
axis remains offshore.

So at this time, confidence is moderate that the first week of May
will remain below average for precipitation. Confidence remains
lower for how far inland (specifically into the Sierra), above
average temperatures will be felt and by when. With the near
record snowpack in the Sierra, any extended period of well above
average temperatures will remain a hydrologic concern, and we
will continue to keep a close eye on that potential. -Zach

* The Week 2 Outlook discussion is an experimental part of the Area
  Forecast Discussion. This product is designed to highlight the
  potential for significant pattern changes beyond day 7 and will
  not be issued on a daily basis.

&&

.AVIATION...

The storm track will move from north of the Oregon border today back
into the Sierra and western Nevada tonight. The storm isn`t very
strong but could bring periods of CIG/VIS restrictions and terrain
obscuration to Sierra terminals through Monday night with
intermittent light showers to western Nevada.

Gusty winds this afternoon of around 25 kts will weaken overnight,
but likely stay breezy around 10 kts. Slightly stronger winds are
forecast for Monday with gusts up to 30-35 kts. Ridge winds will
increase overnight and could gust as high as 70-80 kts at times
creating mountain wave activity. LLWS could occur around some
terrain features, but is not expected to be widespread. -Zach

&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 11 AM to 8 PM PDT Monday for Pyramid
     Lake in NVZ004.

     Lake Wind Advisory from 8 AM to 8 PM PDT Monday for Lake Tahoe
     in NVZ002.

CA...Lake Wind Advisory from 8 AM to 8 PM PDT Monday for Lake Tahoe
     in CAZ072.

&&

$$

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



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