Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 230428 AAA

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
928 PM PDT Thu Mar 22 2018

The atmospheric river system was exiting the region with drier air
aloft bringing decreasing precipitation and clouds from north to
south. Snow and lower elevation rain was winding down across Mono
and Mineral Counties and we will be canceling the winter storm
warning for Mono County as heavy snow has ended for all but the
high Sierra crest near Mammoth. The rain changed over to snow at
KMMH earlier this evening and will come to an end by 11 pm.

Most creeks and streams were also beginning to wind down as snow
levels dropped toward the end of the precipitation event and also
because precipitation has ended for many areas. The Susan River
saw a second rise this evening probably related to a band of heavy
rain that moved across the area early in the evening, but now is
trending down for the night. Meanwhile, the Middle Fork of the
Feather River continues to rise steadily and will reach flood
stage sometime early Friday afternoon. A flood warning is in
effect for the Middle Fork Feather River for minor to locally
moderate flooding from Beckwourth to Sloat including Portola.

A quick look at the 00Z NAM/GFS for this weekend shows little
change from previous thinking with a couple of fronts working into
the northern Sierra and northwest NV with a threat for light
snowfall. Attention will be placed on these features tonight as
some impacts are likely, especially for the Tahoe Basin and
northeast CA. Hohmann


A break in the weather is expected overnight into Friday morning.
Gusty winds develop again Friday afternoon ahead of a couple of
fast moving colder storms that will move through with some snow
for Northeast California into Northwest Nevada this weekend. A
warmer and drier pattern is expected next week with temperatures
trending closer to average for late March.


.PREVIOUS DISCUSSION... /Issued 209 PM PDT Thu Mar 22 2018/

An atmospheric river storm will exit the region tonight with rain
and snow ending this evening. Some rivers and streams will
continue to run high through the evening. After a break Friday
morning, a couple fast-moving cold storms will move through with
some snow for Northeast California into Northwest Nevada. A
warmer, drier pattern is expected next week with temperatures
trending closer to average for late March.

Rain and mountain snow continue this afternoon south of a Portola
to Gerlach line. Bands of showers and thunderstorms are now
developing on the west slope of the Sierra as expected. These
bands will continue to move through this evening, with periods of
heavy rain and snow. The bands are expected to clear the I-80
corridor by 6 pm, and through Mono/Mineral Counties by midnight.
Additional accumulations up to a foot of snow are possible, mainly
in the higher elevations of Mono County. Lighter accumulations up
to 6 inches are possible above about 6500 feet.

Some threat continues for the Feather River and other small
streams in the lower elevations with the periods of heavy
rainfall. This is discussed in more detail in the hydro section

South and east, other concerns are winds in Mineral County along
Highway 95 near Walker Lake. Gusts up to 60 mph have occurred.
These will continue for another hour or two then back off as the
precip nears. A broken line of thunderstorms have also developed
east of Highway 95 in Pershing and Churchill Counties. These will
continue to progress east into Central Nevada in the next couple

Behind the bands of rain/snow, there is strong subsidence showing
up on satellite imagery that is well handled by the models.
Expect a period of mainly dry weather after this evening with
clearing skies. Temperatures will be a few degrees below average
by morning. X

LONG TERM...Friday Morning through Sunday night...

BOTTOM LINE UP FRONT: Ski commuting into the Sierra Friday evening?
Anyone traveling Friday evening and through the weekend should plan
on snow showers with travel slow downs, delays, and chain controls,
especially in the Sierra and across northern/western Lassen County.
Now that we are in late March, most road impacts due to snow will be
limited to early morning and overnight time frames for lower

Model simulations continue to be very consistent with showing a
break in precipitation during the day on Friday for much of
northeast California and western Nevada. Breezy conditions are
expected to develop in advance of the next disturbances that will
push through the area. Plan on gusty conditions Friday afternoon and
evening with turbulence possible for aviation, choppy conditions for
boating, and restrictions for high-profile vehicles in wind prone

By Friday night the first of two disturbances will drop through the
Sierra and northwestern Nevada. Simulations have trended weaker with
this initial wave. Although it is cold enough to produce snow at all
elevations overnight, the forcing really appears to fall apart as it
drops south toward the I80 corridor, especially for western Nevada.
Plan on scattered light snow showers from Friday night through
Saturday morning for the Sierra and northeast California, mainly
from Alpine county north. Looking at around 1-3" in northeast
California and 3-8" in the Sierra from Alpine County northward.

The second and final disturbance will drop through late Saturday
night into Sunday with the main upper level trough. Although it will
be cold enough for all elevations, there is uncertainty with snow
amounts in this secondary wave. Confidence is medium to high for
additional snow amounts in the Sierra, but lower confidence for snow
chances down into western Nevada. While we may see snow showers
`down here` accumulations should be light. Keep in mind that even
with wet roads, the driving conditions can be slick. Plan on snowy
road conditions and delays up and over Sierra roads with snow in the
forecast from Friday evening and through the weekend. Edan

The upper level trough will be slowly exiting on Monday as a high
pressure ridge amplifies across the Pacific Northwest. As this upper
low will be slow to exit Monday, the southern portion of the trough
closes off and may produce some lingering snow showers mainly south
of Highway 50 through the afternoon. Temperatures will remain quite
cool with temperatures in the higher elevations remaining well below
freezing, and much below normal for valley locations. Gusty north to
northeast winds will persist across ridges into Tuesday on back side
of upper low.

For the latter half of the week, a more springlike pattern is
shaping up with dry conditions and warmer temperatures. Highs will
likely push into the 50s Sierra with 60s for lower elevations by Thu-
Fri. Hohmann


Runoff from the earlier heavy rains in the valleys should be
decreasing through the night as precipitation intensity wanes. There
could still be some very minor flooding in poor drainage and low
lying areas east of the Sierra and across lower elevations of
Lassen...Plumas and Sierra Counties through early evening. This will
allow the nuisance flooding to subside.

Snow levels have fallen in the Tahoe area...but minor ponding on
many streets is still possible through the night as water may not
have the ability to drain due to all of the snow in place.

We have issued a Flood Warning for the Middle Fork Feather River
near Portola. Runoff from this storm is likely to push the river
above flood stage late Friday afternoon. The river is forecast to
peak around 9 feet on Saturday. Flood stage is 8.5 feet. At the
level of the forecast...there should not be significant impacts in
Portola...but downstream toward Clio there could be increased
flooding. This would be associated with both the river and flow out
of Sulphur Creek near CA Highway 89.


.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 11 PM Friday to 5 AM PDT Sunday

CA...Winter Weather Advisory from 11 PM Friday to 5 AM PDT Sunday

     Winter Weather Advisory from 11 PM Friday to 5 AM PDT Sunday



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