Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 211606

Area Forecast Discussion
National Weather Service Reno NV
906 AM PDT Wed Mar 21 2018


Only a minor update this morning to adjust some high temperatures
down. With abundant clouds expected and continuing precipitation
we most likely will not see highs climb as much as previously
forecast. There still looks to be a break for western Nevada with
increasing winds; that will help raise temperatures...just maybe
not as much as we originally thought.


.PREVIOUS DISCUSSION... /Issued 338 AM PDT Wed Mar 21 2018/


An atmospheric river type storm begins to push into the region
today with the heaviest precipitation expected tonight into
Thursday. This will bring periods of heavy valley rain and heavy
high Sierra snow along with gusty winds. The weekend will be
colder with snow showers possible down to all valley floors. Drier
conditions are looking more likely for next week.


Main concern in the short term forecast remains our incoming moderate
to strong Atmospheric River type storm. Here is a summary of the
characteristics of the storm with additional details below:

* Precipitation is ongoing today but expect the peak of the storm to
  arrive tonight into Thursday.

* This is a high snow level storm with multiple feet of heavy, wet
  snow expected in the high Sierra. This will mainly be a moderate
  to heavy rain event for most populated valley areas.

* Areas of urbanized flooding from snowmelt runoff are possible in
  poor drainage areas where debris or snow blocked drainages exist.
  Small creeks and streams below 8,000` could see minor flooding.
  Main stem rivers will see rises but will remain below flood stage.

* Gusty winds expected today and Thursday. This combined with
  heavy Sierra snowfall has prompted a Backcountry Avalanche

TIMING: Precipitation will be ongoing today but expecting the
heaviest precipitation to arrive tonight into Thursday. Moderate to
heavy precipitation continues Thursday afternoon before quickly
diminishing Thursday evening.

SNOW LEVELS: Snow levels today will hang in the 8,000-8,500` range
from the Tahoe Basin extending southward into Mono County. Snow
levels will begin to fall Thursday afternoon reaching about 7,000`
in the Tahoe Basin and 8,000` in Mono County. By late Thursday
afternoon and early evening, snow will be possible at Lake Tahoe
level and along portions of Hwy 395 through Mono County.

RAIN/SNOW: Sierra snow totals remain largely unchanged with the
highest totals expected in the Sierra in Mono County (2-4 feet above
mainly 8,500` with localized 5+ feet along the crest). The Tahoe
Basin will see up to 2-3 feet mainly above 7,500` with localized
areas up to 4 feet along the crest. A few inches will be possible at
Lake Tahoe level by Thursday evening, but by the time snow levels
drop much of the precipitation will be ending.

Snow totals in the 7500-8000` remain particularly challenging and
have the biggest boom/bust potential. Mammoth Lakes in particular is
on the fringe but latest analysis puts it in 5-10" range with a few
inches possible through the Highway 395 corridor in Mono County.

This will be a rain event for western Nevada with moderate to heavy
rain expected on Thursday. 0.50" of rain is possible across western
Nevada valleys with 0.75-1+" possible closer to foothill areas.

LONG TERM...Friday onward...

There will be a break in precipitation through Friday afternoon or
evening before an incoming cold front and associated trough bring
another round of snow to the region. The best chances for
accumulation will be in the Sierra from Tioga Pass north and
northeast California; with light accumulations also possible in
western Nevada. With snow levels at all valley floors, even light
accumulations may bring travel impacts across the region. Breezy
winds are also expected on Friday ahead of the cold front with the
strongest winds mainly from I-80 north. Expect choppy conditions on
area lakes and possible travel concerns for high profile vehicles
along with turbulence for aviation.

A final passing shortwave could bring additional chances for snow
Saturday night into Sunday. The intensity and timing of this feature
have been changing in the past several model runs, so confidence
remains lower. Will keep general low end chances for precipitation
in the forecast with additional light snow accumulation possible.
Considering we are getting into the latter part of March, most road
impacts from these lighter snows will be limited to the overnight
and early morning hours outside of higher elevation mountain passes.

A ridge begins to build over the west coast next week leading to a
drying trend. While the week will start out cool with the region
under northerly flow, temperatures look to gradually moderate to
near or slightly above normal by the middle or end of the week.


A system is bringing valley rain and mountain snow to the region
this morning with localized MVFR-IFR conditions and widespread
terrain obscuration. Precipitation will continue in the Sierra and
northeast California through much of today, but is unlikely in
western Nevada.

A much stronger storm is on tap for tonight through Thursday with
strong and gusty winds, and moderate to heavy mountain snow and
valley rain. Terminals should all just see rain, but expect
widespread mountain obscuration and periods of MVFR-IFR ceilings
and visibility.

Winds will bring turbulence and wind shear, with localized studies
indicating LLWS possible for KRNO today into Thursday. The most
likely periods for strongest valley winds will be Wednesday and
again Thursday afternoon, where widespread gusts of 25-35 kts are
possible. The time frame in between will have heavy precipitation
which will dampen the wind speeds, however erratic stronger wind
gusts are possible.

Another period of breezy winds is likely Friday ahead of a cold
front. This front will bring another round of snow to the region
Friday night with accumulating snow likely for KTRK and KTVL and a
chance for light accumulations in western Nevada as well, including
KRNO and KCXP. Additional snow showers are possible Saturday night
through Sunday with the potential for minor accumulations,
especially from 03z-15z. -Dawn


.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory until 5 PM PDT this afternoon for Lake Tahoe
     in NVZ002.

     Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Friday
     above 7000 feet in NVZ002.

     Flood Watch from this evening through late Thursday night below
     7000 feet in NVZ002.

     Lake Wind Advisory until 8 PM PDT Thursday for Pyramid Lake in

CA...Flood Watch from this evening through late Thursday night CAZ071.

     Flood Watch from 5 PM PDT this afternoon through late Thursday
     night below 7500 feet in CAZ073.

     Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Friday
     above 7500 feet in CAZ073.

     Lake Wind Advisory until 5 PM PDT this afternoon for Lake Tahoe
     in CAZ072.

     Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Friday
     above 7000 feet in CAZ072.

     Flood Watch from this evening through late Thursday night below
     7000 feet in CAZ072.



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