Lake Wind Advisory 19, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
256 PM PDT Wed Apr 5 2017

.SYNOPSIS...

Gusty winds this afternoon will weaken overnight, but increase
even more Thursday and continue into Saturday morning. The
strongest winds are expected Friday. Heavy rain and higher
elevation snow will occur late Thursday night into Saturday
morning with the heaviest precipitation Friday morning. A drier
pattern is likely for early next week with another moderate storm
possible for the end of next week.

&&

.SHORT TERM...
The focus continues to be on the storm for late tomorrow through
Saturday with only minor changes. Until then, gusty winds this
afternoon will diminish in the valleys overnight, but the ridge
winds will continue their increase. Cloud cover will increase more
tonight as well with one more mild night overall as we head into
Thursday where winds increase further.

Confidence remains high in a strong storm Thursday night into
Saturday with heavy precipitation and gusty winds. It remains
lower for snow levels, snow amounts and flood potential. Here are
the details:

PRECIPITATION: A few light showers are possible Thursday, but it
is Thursday night into Friday morning that the main atmospheric
River (AR) hits. The heaviest rates will be from midnight
tomorrow night into Friday morning, at least from Highway 50
north. A bit of a break before the next wave hits Friday night
there although rates won't be quite as high. South of Highway 50,
the heaviest rates will occur Friday and with the brunt of the
storm looking more likely to hit here, rates may not back off at
all until Saturday morning. Saturday looks to be more showery, but
there are differences as the GFS is much weaker with the last
short wave while the EC is consolidated. The EC would see one more
burst of moderate to heavy precip during the day Saturday.

Overall forecast amounts haven't changed much with 3-5 inches of
water along the Sierra Crest and 1.5-3 inches along and west of
the 395 corridor including the Tahoe Basin. Further east, 0.5 to
1.5 inches of rain in the valleys with the higher amounts along
the Sierra Front and the lighter amounts for the Highway 95
corridor.

SNOW LEVELS: They continue to be a bear and the overall forecast
uncertainty lies here. Our best estimate still is to start at
6500 feet near the Oregon border, 7000-7500 feet around Tahoe,
and 8500 feet around Mono County with the initial push into Friday
morning before lowering about 1000 feet Friday afternoon. They
remain there before crashing to all valley floors behind the main
cold front Saturday morning. Several feet of snow are likely above
the 8000 foot level, but from there to 6000 feet amounts are up
in the air. Some models show snow levels not getting above
6500-7000 feet, while others keep them near 8000 feet for a longer
period of time. Snowfall amounts could range from just a few
inches to well over a foot. The snow level will also impact
potential hydrology issues, see below.

HYDROLOGY: With snow levels and total precip not looking to be
excessively high overall, the threat is not as high as it could
be. Rises will occur on all area creeks and rivers and several of
the mainstem rivers will likely hit monitor stage. However, the
brief period of intense precip will likely keep them from getting
out of hand. That said, any changes for the worse in snow levels
and heavy precip duration could result in significant changes to
river forecast.

Our biggest concerns remain with the smaller creeks and streams at
lower elevations. Soils still very moist from the past winter, and
rapid rises with flooding issues are possible. Small debris flows
and rock slides are also possible in the Sierra. Many terminal
lakes will also see rises due to the increased runoff including
Swan, Silver, White, Washoe and Honey Lakes. Of most concern
remain Silver and Swan Lakes where 1-2 inches of rain will fall
with the lower amounts on the valley floor and the higher amounts
in the headwaters on Peavine. A flood watch remains in effect for
all lower elevation areas in the Sierra and Sierra Front.

WINDS: They increase Thursday with most areas gusting to 40-50 mph
and up to 100 mph over Sierra Ridges. 700 mb winds peak 06-18Z
Friday at near 70 kts so the ridges may gust to near 150 mph.
Lower elevations however, likely won't see their full potential
due to the spillover expected. Brief periods of stronger winds are
likely just ahead of the precip Thursday evening and again Friday
afternoon. Based on this, we will continue to lump the winds with
the Winter Storm statements in the mountains and go with wind
advisories for the Surprise Valley and along the Sierra Front.
Further east out of the main spillover zone, the winds have the
potential to be stronger Friday afternoon and evening. Therefore,
will hoist a High Wind Watch there where sustained winds around 40
mph and gusts around 60 mph are possible for at least a couple
hours.

Bottom line...

Expect many travel impacts beginning late tomorrow afternoon and
continuing into Saturday evening due to rain, snow and wind.
Mountain travel may become especially hazardous over passes due to
potentially heavy snow and strong winds Friday morning into
Saturday morning. As far as preparation, complete it by tomorrow
afternoon if at all possible. We also recommend keeping flood
mitigation measures from the winter in place through the spring.
Wallmann

.LONG TERM...Saturday Afternoon through Next Week...

By Saturday afternoon the cold pool will be over the Sierra with
snow levels down to around 4000 feet. Most models have the
precipitation changing to showers by Saturday afternoon. However,
some recent simulations now have a fairly significant wave coming
through bringing another round of heavy snowfall to the Sierra
Saturday afternoon. If this were the case, travel in the Sierra
could stay challenging through the day on Saturday with snow impacts
possible in western Nevada Valleys.

Weak ridging builds in Sunday with another weak trough passing by to
the north on Monday. Sunday through mid-week will see a decent
warming trend with daytime high temperatures rebounding to near
Normal by Tuesday.

Then guess what, another storm is possible by the second half of
next week. The pattern becomes more amplified next week with faster
moving storms again dropping out of the Gulf of Alaska. Recent
models simulations are in good agreement today of another fairly
strong system dropping out of the Gulf of Alaska bringing an
additional, potentially strong spring storm, to the Sierra. -Zach

&&

.AVIATION...

Ridge winds around 40 kts today will continue to pick up tonight as
a significant late season storm approaches. As ridge winds pick up
overnight and surface winds begin to subside a period LLWS is
possible.

Thursday surface wind gusts increase to 30-40 kts ahead of the
storm. Thursday night through Saturday aviation will be impacted by
strong winds, rain and snow. 700 mb winds increase to 60-70 kts with
mountain wave/turbulence likely and periods of LLWS possible. Very
heavy rain and mountain snow will bring long periods of reduced
CIGs/VIS to Sierra terminals with heavy rain expected for KRNO/KCXP
Friday. Snow accumulations for Sierra terminals could range from a
few inches to a foot or more. By Saturday light snow accumulations
of snow/snow pellets will be possible for KRNO/KCXP. -Zach

&&

.REV Watches/Warnings/Advisories...
NV...Flood Watch from late Thursday night through Saturday morning
     NVZ002-003.

     Wind Advisory from 11 AM Thursday to 11 PM PDT Friday NVZ003-005.

     Lake Wind Advisory from 8 AM Thursday to midnight PDT Thursday
     night for Lake Tahoe in NVZ002.

     Winter Storm Watch from late Thursday night through Saturday
     afternoon NVZ002.

     High Wind Watch from Friday morning through Friday evening
     NVZ001-004.

     Lake Wind Advisory from 11 AM to 8 PM PDT Thursday for Pyramid
     Lake in NVZ004.

CA...Flood Watch from late Thursday night through Saturday morning
     CAZ071>073.

     Winter Storm Watch from late Thursday night through Saturday
     afternoon CAZ071.

     Wind Advisory from 11 AM Thursday to 11 PM PDT Friday CAZ070.

     Winter Storm Watch from late Thursday night through Saturday
     afternoon CAZ073.

     Lake Wind Advisory from 8 AM Thursday to midnight PDT Thursday
     night for Lake Tahoe in CAZ072.

     Winter Storm Watch from late Thursday night through Saturday
     afternoon CAZ072.

&&

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