Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 151121
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
321 AM PST Wed Nov 15 2017

.SYNOPSIS...

A strong atmospheric river storm will impact the region today into
Thursday. Strong and damaging winds are expected this afternoon
across western Nevada along with high wildfire danger before
precipitation arrives. Heavy rain and mountain snow will arrive
this afternoon into Thursday in the Sierra with high snow levels
expected. A cold front will drop snow levels tonight into
Thursday and will provide heavy spillover rainfall for western
Nevada.

&&

.SHORT TERM...

A strong Atmospheric River (AR) storm is set to impact the Sierra
and western Nevada beginning today and persisting into Thursday.
This storm will be the strongest of the fall season so far in
terms of winds and precipitation. Strong and potentially damaging
winds are expected by this afternoon and will persist into early
Thursday morning as a cold front arrives. The front will lower snow
levels and produce heavy spillover into the western Nevada and
northeastern California valleys after about midnight.

What`s changed/What hasn`t in this morning`s forecast:

* Precipitation totals were further increased mainly through
  foothill and western Nevada valley locations to account for
  good spillover potential tonight into Thursday.

* Strong and damaging wind potential is still on track for the
  Sierra Front and Highway 395/I-580 corridor. High wind warnings
  are in place for this afternoon through Thursday morning. Some
  trend for the wind threat to last a bit longer and persist until
  the cold front moves through later tonight/Thurs AM.

* No significant changes in timing of the winds, rain, snow level
  drop and high Sierra snowfall totals. See sections below for
  additional details.

TIMING:

Wind:
Strong winds are currently developing across the mountain ridges.
Valley locations will see strong winds by this afternoon and
evening. Wind gusts of 55-70 mph will be widespread mainly from
the Carson Valley through Reno and into northern Washoe County.
Wind prone locations could see localized 70+ mph gusts.

Aviation impacts expected along with road restrictions for high
profile vehicles. Blowing dust will be a concern for areas east of
Reno, especially for Churchill, Pershing, and Mineral counties.
High winds will also lead to critical fire weather conditions for
the lower elevations along and east of Highway 395 where dry
vegetation still exists.

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

Heavy rain will also be a big test for the hydrologic system, as
we will see steep rises on area rivers, creeks, and streams. No
flooding is expected at this time with mainstem rivers, although
significant rises are expected. Minor flooding of smaller creeks,
streams, and urban areas will be possible tonight into Thursday
morning.

PRECIPITATION:

Tahoe Basin & Northeast CA:
Liquid totals through Thursday evening still look solidly in the
3-4" range with up to 6" right along the Sierra crest. Heaviest
snowfall will generally remain above 8,000 feet where 2-3 feet of
heavy wet snow is possible. Localized areas of 4`+ are possible in
higher terrain right along the Sierra Crest. Snow levels should
begin to fall after midnight tonight at which point winter travel
impacts may begin on the passes. Snow levels are hanging up for a
longer period of time and may not fall all the way to Lake Tahoe
level until Thursday evening, with a couple inches of snow
Thursday night into Friday morning.

Mono County:
Liquid totals through Thursday evening look similar and in the
2-4"+ range with up to 6" right along the Sierra crest. Snow
levels will be a bit higher and in the 8,000-8,500` range. Snow
totals in the high Sierra over 8000 feet will be around 2-3 feet
with localized areas up to 4`+ along the Sierra Crest.

Precipitation totals continue to remain lower confidence in Mono
County however as some model guidance continues to show a longer
duration of heavier precipitation. Latest guidance has slightly
come into better agreement with a longer duration but still quite
a spread remains the totals.

Western Nevada:
Spillover rainfall looks to occur in about a 6-12 hour window
roughly after midnight tonight into Thursday morning through
about the I-80/Hwy 50 corridor before the front pushes south
through the region Thursday morning.

Rainfall amounts have increased to around 1.0"-1.75" through the
Hwy 395/I-580 corridor with 1.5-2.5" possible for western
foothill areas through Thursday night. 0.25"-0.50" is possible
across the Basin and Range including areas such as Lovelock and
Fallon. Fuentes


.LONG TERM...Saturday through next week

Latest guidance trends now favor keeping both days of this weekend
dry, as flat ridge moves eastward across the Great Basin. The next
Pacific storm is showing signs of splitting before reaching the west
coast, which would delay its inland arrival until early next week.

Saturday will remain relatively cool with inversion conditions
producing limited mixing. By Sunday, some warming is likely with
highs near 60 degrees in some valleys as southwest flow aloft
increases, although surface winds will still be relatively light.

Another Pacific storm system is then projected to reach the eastern
Sierra by the Monday-Tuesday time frame. This storm continues to
have variable snow level scenarios, ranging from near 6000 feet to
above 9000 feet. We are still leaning toward the warmer side of the
guidance range (snow levels likely above 8000 feet) as the
downstream longwave pattern continues to favor a deeper trough over
the eastern US, which typically keeps the west milder. The strength
of this system and precip amounts also vary with the guidance
sources, as the warmer scenarios may tap into a deeper source of
subtropical moisture and produce a period of enhanced rainfall,
especially north of I-80. However, next Monday and Tuesday continue
to be a period of below average forecast confidence due to the range
of possibilities with the track of this storm.

After this storm pushes through, the overall trend favors a few dry
days leading into Thanksgiving as high pressure ridge builds from
the southwest US into the Great Basin. Southwest flow aloft is
projected over the Sierra with the primary storm track shifting
northward to far northern coastal CA and the Pacific Northwest. A
few light showers could brush across far northeast CA, but the more
likely outcome would be areas of mid-high level cloud cover across
eastern CA-western NV. This weather pattern would also bring a
decent amount of warming, with highs pushing into the 60s for
western NV valleys toward the mid-late portions of next week. While
there are still some uncertainties with next week`s weather pattern,
at this time there do not appear to be significant weather impacts
for the early part of the Thanksgiving holiday peak travel period.
MJD

&&

.AVIATION...

A powerful storm system will affect the Sierra and western Nevada
through Thursday. This storm will be the strongest so far this
season with more precipitation, strong winds, and eventually
lowering snow levels by Thursday.

Winds will continue to increase across mountain tops and work down
to valley floors later this morning into this afternoon. LLWS
will be likely as southerly winds develop across valleys and
southwest ridge level winds increase to 55-70 kts with gusts
approaching 90kt. The period from 18Z today 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 this afternoon and evening ahead of the
precipitation band.

Rain will reach the Sierra by this 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 they will
remain fairly steady. Also 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
tonight 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, accumulation is
going to be limited to later Thursday and Thursday night as snow
levels will be a bit slower to fall tonight and early Thursday
than previously thought. A couple inches are possible at KTRK/KTVL
Thursday night with lesser confidence in an inch or two at KMMH.
Hohmann/Edan

&&


.REV Watches/Warnings/Advisories...
NV...High Wind Warning from 10 AM this morning to 4 AM PST Thursday
     NVZ003-005.

     Red Flag Warning from 10 AM this morning to 7 PM PST this
     evening NVZ450.

     Winter Storm Warning from 4 PM this afternoon to 4 AM PST Friday
     above 7000 feet in NVZ002.

     Red Flag Warning from 10 AM this morning to 7 PM PST this
     evening NVZ453-459.

     Wind Advisory from 10 AM this morning to 4 AM PST Thursday
     NVZ001-004.

CA...Winter Storm Warning from 4 PM this afternoon to 4 AM PST Friday
     above 6000 feet in CAZ071.

     High Wind Warning from 10 AM this morning to 4 AM PST Thursday
     CAZ070.

     Red Flag Warning from 10 AM this morning to 7 PM PST this
     evening CAZ273.

     Winter Storm Warning from 4 PM this afternoon to 4 AM PST Friday
     above 8000 feet in CAZ073.

     Winter Storm Warning from 4 PM this afternoon to 4 AM PST Friday
     above 7000 feet in CAZ072.

&&

$$

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



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