Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 202328
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
328 PM PST Mon Feb 20 2017

.SYNOPSIS...

A powerful atmospheric river storm will continue to bring very
heavy precipitation, heavy snow and strong winds to the region through
Tuesday. A secondary cold front has the potential to bring light
snow accumulations to western Nevada valley floors Tuesday night.
Cool and shower weather is expected for the remainder of the week
with the potential for a colder storm next weekend.

&&

.SHORT TERM...

Current radar shows the main precipitation band impacting the
Sierra from highway 50 north into far northeast California with
moisture stretching off the coast. This plume of moisture has
been slowly moving north over the day with effective spillover
into western Nevada. The Reno airport has already picked up over
0.5" of precipitation. Per webcams and surface temperatures, snow
levels appear to be hovering around 5000-5500 in NE California,
6000-6500 feet around the Tahoe Basin, and 7500-8000 feet in Mono
County.

Precipitation is expected to intensify in NE California this
evening as the strong atmospheric river continues to be aimed in
that direction. As the upper level low continues to move onshore
the heaviest precipitation will slowly be forced south again
pushing from north to south through the Sierra. Snow levels today
have stayed a few hundred feet lower then anticipated due to the
heavy precipitation rates and the AR staying pointed more directly
at the Tahoe area. Snow levels may still rise a bit this
afternoon, but are no longer expected to rise above 7000 feet.
This is good news for the flooding concerns in western Nevada, but
not so much for anyone trying to travel in the Sierra tonight.

This evening snow levels are expected to start dropping again as
the upper level low pressure makes it`s way onshore. By tomorrow
morning snow levels should lower down to around 4500` in NE
California, 5000` around Tahoe, and 6500` in Mono County.
Precipitation will begin to taper off by early tomorrow morning.
This could bring another 6-10 inches of snow to the Truckee/Tahoe
area with a few inches of snow possible down to the western Nevada
foothills.

As the initial upper front moves in this evening, another few
hours of heavy rain is expected to spill into western Nevada. A
stronger cold front moves through Tuesday night and this will be
the best chance for snow to accumulate down to western Nevada
valley floors. Moisture should be limited by this point so
accumulations should be less then 1/2 an inch if snow does
accumulate.

Winds have been relatively light in western Nevada today as heavy
precipitation has kept winds from mixing to the surface. There
could still be a burst of strong winds for 2-3 hours tonight as
precipitation tapers off. The peak would probably be around
midnight. -Zach


.LONG TERM...Thursday through Monday...

An upper trough is expected to keep below average high temperatures
in place for northeast CA and western NV through the long term
period. With the trough off the coast and westerly flow aloft in
many simulations, isolated to scattered snow showers are expected
through at least Friday night. With no major forcing most showers
should remain light, at least east of the Sierra, so impacts
currently look minor.

Saturday and Sunday, uncertainty rises significantly as simulations
diverge with the track of the trough and how much moisture it taps
into from the Pacific. The 12Z EC and at least the last couple runs
of the GFS show the potential for significant precipitation between
Saturday night and Sunday night, with the 00Z EC delayed but still
showing a decent shot at precipitation by Monday morning. With
sufficiently cold air in place in most simulations, especially north
of Highway 50, there is the potential for significant snow even out
into western NV. Confidence is low at this time given the timing and
moisture discrepancies. Also, as we are moving later into winter
snowfall impacts to roads can be heavily influenced by the time of
day and snowfall rates given intensifying insolation (lighter snow
may just result in wet roads late morning-afternoon). Snyder

&&

.AVIATION...

Widespread terrain obscuration with turbulence expected into Tuesday
morning for northeast CA and western NV. There will also be pockets
of LLWS within 010-020 AGL, especially during periods of lighter
precipitation (heavier precipitation tends to dampen out mountain
waves). Any LLWS should transition to mechanical turbulence with
gusty winds behind a cold front Tuesday with the exception of KTVL
due to channeling winds in the Upper Truckee drainage.

Snow levels generally between 6000-7000 ft MSL into early evening to
fall below 5500 ft MSL Tuesday morning north of Highway 50 as a cold
front moves through. For Sierra terminals this will bring
accumulating snows to paved areas/tarmacs, with at least 3-6 inches
for KTVL/KTRK and up to 3 inches for KMMH from midnight Tuesday
through Tuesday morning. For the lower valley terminals of northeast
CA and western NV, the general timing for the transition to snow
Tuesday is 5-8 AM around KSVE, 10 AM for KRNO/KCXP/KMEV, and 1-4PM
for KLOL/KNFL. A quick slushy accumulation up to an inch or two will
be possible for KSVE/KRNO/KCXP/KMEV, especially if snow is moderate
to heavy. Any snowfall in the lower elevations should melt off paved
areas by afternoon. Snyder/Wallmann

&&

.HYDROLOGY...

* Major flooding is possible for the Middle Fork of the Feather
  River near Portola. Minor to moderate flooding is forecast Tuesday
  to Thursday.
* Flooding likely for creeks, streams, urban areas and drainage
  basins in the Tahoe Basin, eastern Sierra, northeast California
  and western Nevada early Monday through early Tuesday.
* Snow levels below 7000 feet are minimizing flood impacts around
  the Tahoe Basin.

So far the big story today is the lack of a rise in the snow level,
which is helping to minimize the flood threat especially around the
Tahoe Basin. Snow level profilers across northern California have
reported snow levels of 6000 to 6500 feet, with a couple readings
slightly below 6000 feet as 2pm. Models are projecting snow levels
may rise to near 7000 feet with the surge of heavy precipitation
between 4 and 10 pm this evening. This is looking like period with
greatest risk for flooding across western Nevada, especially in
urban areas and along creeks and streams.

Widespread heavy precipitation should end around midnight, though
band of showers will persist into Tuesday. Fortunately snow levels
will drop off tonight and could fall as low as 4500-5000 feet.

However once the rain ends, high flows will continue on the lower
reaches of the Carson and Truckee Rivers into Tuesday. The Middle
Fork of the Feather River may remain above flood stage until
Thursday as water drains out of the Sierra Valley. Brong

&&

.REV Watches/Warnings/Advisories...
NV...Wind Advisory until 4 PM PST Tuesday NVZ005.

     Flood Watch through Tuesday morning NVZ002.

     Winter Storm Warning until 4 PM PST Tuesday NVZ002.

     High Wind Warning until 4 PM PST Tuesday NVZ001.

     Flood Watch through Tuesday morning NVZ003.

     Wind Advisory until 4 PM PST Tuesday NVZ003-004.

CA...Flood Watch through Tuesday afternoon CAZ071.

     Winter Weather Advisory until 4 PM PST Tuesday CAZ071.

     Wind Advisory until 4 PM PST Tuesday CAZ070.

     Flood Watch through Tuesday morning CAZ073.

     Winter Storm Warning until 4 PM PST Tuesday CAZ073.

     Flood Watch through Tuesday morning CAZ072.

     Winter Storm Warning until 4 PM PST Tuesday CAZ072.

&&

$$

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



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