Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 141126
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
326 AM PST Tue Nov 14 2017

.SYNOPSIS...

A moderate atmospheric river storm is expected to impact the
region Wednesday into Thursday. Strong and gusty winds are
expected Wednesday afternoon across western Nevada. Heavy rain
and mountain snow will arrive Wednesday into Thursday in the
Sierra with high snow levels expected. A cold front will drop snow
levels Wednesday night and Thursday morning and will provide
spillover rainfall across western Nevada.

&&

.SHORT TERM...

The main concern in the short term forecast is with an incoming
solid moderate level Atmospheric River (AR) storm on Wednesday
and Thursday. This storm is looking to be strongest so far of the
season in both winds and precipitation. The overall theme for
this storm is that it will provide strong winds Wednesday
followed by heavy rain and heavy high elevation snowfall through
the Sierra Wednesday into Thursday. Snow levels will remain high
through the bulk of the precipitation but will quickly fall
Wednesday night into early Thursday morning as a cold front moves
through. It is during this cold frontal passage that western
Nevada will see good spillover rainfall.

Update summary to the forecast this morning:

* This system has been trending warmer, wetter, and windier. This
  trend continues and have increased precipitation totals
  particularly across western Nevada where spillover is looking
  much better.

* Continued to raise snow levels Wednesday afternoon and evening.
  The likelihood for accumulating snow below 7,500` is decreasing
  until the front passes. Heavy wet snow expected for elevations
  above 8,000` through the Sierra. Also included Mono County
  locations above 8,000` in the Winter Storm Watch.

* Winds also are trending stronger. Have issued a High Wind Watch
  for portions of western Nevada from the Carson Valley through
  Reno and into far northern Washoe County.

TIMING:

Precipitation: Moderate to heavy rainfall arriving my mid-
afternoon in the northern Sierra with the peak intensity occurring
from Wednesday late afternoon through Thursday morning. Heavier
precipitation won`t arrive in Mono County until Wednesday
evening. Spillover rainfall for western Nevada will arrive with
the front probably until after midnight and will persist into
early Thursday morning.

Wind: Strongest winds are expected Wednesday afternoon and evening
and will decrease after the front moves through early Thursday
morning. Wind gusts of 50-60 mph look to be widespread mainly from
the Carson Valley through Reno and into northern Washoe County.
Wind prone locations could see localized gusts between 60-70 mph.
Aviation impacts expected along with road restrictions for high
profile vehicles.


PRECIPITATION:

Tahoe Basin & Northeast CA:
Liquid totals through Thursday evening look solidly in the 2-3"
range with up to 3.5"+ right along the Sierra crest. Heaviest
snowfall will generally remain above 8,000 feet where 1-2 feet of
heavy wet snow is possible. Small and localized areas of 2.5-3
feet are possible right along the crest. Snow levels should begin
to fall after midnight at which point winter travel impacts may
begin on the passes. Snowfall is possible at lake level Thursday
morning but only looking like a few inches at this point as the
bulk of the moisture will have moved south by this time.

Mono County:
Liquid totals through Thursday evening look similar and in the
2-3+" range. Snow levels will be a bit higher and in the
8,000-8,500` range. Snow totals in the high terrain also in 1-2`
with localized areas up to 3`. Precipitation totals are lower
confidence in Mono County however as some model guidance keep a
longer duration of heavier precipitation. Current forecast would
be on the conservative side as a result.

Western Nevada:
Spillover rainfall looks to occur in about a 6 hour window roughly
after midnight through about the I-80/Hwy 50 corridor before the
front pushes south through the region Thursday morning. Rainfall
amounts of 0.50"-0.75" are possible through the Hwy 395/I-580
corridor with amounts closer to 0.25" across the Basin and Range
including areas such as Lovelock and Fallon. Fuentes


.LONG TERM...Friday through early next week

The midweek storm is expected to exit western NV by the end of the
week, although some leftover rain and snow showers are possible
Friday morning, with snow levels down near 4500 feet. For the
remainder of Friday into Saturday, a flat ridge will keep dry
conditions with areas of high clouds over the region, with highs a
few degrees below average Friday then trending warmer going into the
weekend.

Another Pacific storm system is then projected to reach the eastern
Sierra by the Sunday-Monday time frame. This storm currently looks
to be on the warm side with snow levels likely remaining above 8000
feet. The latest guidance is also trending toward a split trough,
but disagrees on whether the split occurs before or after this
trough moves inland. The offshore splitting scenario would keep most
precip limited to the Sierra, while the inland scenario would
potentially bring a short period of rain to lower elevations of
western NV. The longwave pattern downstream seems to be favoring the
ridge prevailing between the Rockies and the central US while a cold
trough digs over the eastern US, which would probably be sufficient
to split the incoming trough before it reaches the Sierra. However,
this is a period of below average forecast confidence due to the
range of possibilities with the track of this trough. At this time,
we will start with better precip chances near the Sierra and
northeast CA, but relatively modest rain chances across western NV
valleys. MJD

&&

.AVIATION...

Today will be relatively quiet with winds diminishing this morning
and clouds clearing as trough exits.  Another storm system begins to
affect a larger part of the region Wednesday through Thursday. This
storm will be stronger with more precipitation, strong wind
potential, and lowering snow levels by Thursday.

Winds will begin to ramp up across ridges tonight and then increase
further Wednesday. LLWS will be likely by midday Wednesday as
southerly winds develop across valleys and southwest ridge level
winds increase to 50-60 kts with gusts approaching 90kt. The period
from 18Z Wednesday to 06Z Thursday appears to be the most critical
window for wind, especially for the eastern Sierra along the Highway
395 corridor extending out to Hwy 95. Sustained winds 25-35 kts with
gusts to 50 kts will be widespread and there could even be a period
of stronger winds from Reno south toward KMMH late Wednesday
afternoon and evening ahead of the precipitation band.

Rain will reach the Sierra Wednesday afternoon and will spill over
into western NV along and north of I-80. As this rain band shifts
southward overnight, surface winds will ease although ridge level
winds are going to remain strong and turbulence will persist.
Moderate to occasionally heavy rain in the Tahoe Basin will push
CIGS/VSBY down to MVFR levels Wednesday night into Thursday morning.
This band of rain will shift southward into the eastern Sierra of
Mono County for Thursday with lowering CIGS/VSBY at KMMH. As far as
snowfall, several inches may accumulate at KTRK/KTVL Thursday
morning as snow levels fall. Hohmann

&&

.REV Watches/Warnings/Advisories...
NV...High Wind Watch from Wednesday morning through late Wednesday
     night NVZ003-005.

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

CA...Winter Storm Watch from Wednesday afternoon through late
     Thursday night CAZ071.

     Winter Storm Watch from Wednesday afternoon through late
     Thursday night above 8000 feet in CAZ073.

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

&&

$$

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



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