Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 151115
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
315 AM PST Wed Feb 15 2017

.SYNOPSIS...
High pressure will maintain dry and mild conditions across the
Sierra and western Nevada through today. A windy, wet pattern
sets up across the region starting late tonight. Multiple storms
may impact the area from tonight through early next week. Keep
flood mitigation in place or readily available through at least
the next week.

&&

.SHORT TERM...
Main changes to the short term were for the first storm coming in
late tonight and early Thursday. Model simulations continue to
trend stronger with the winds, so we have issued a high wind watch
for the Tahoe Basin and for areas along the Highway 395/I580
corridor from Susanville to Reno and southward through Mono
County.

Today: Dry and mild conditions along with light winds will
continue today. Today is your last day to prepare for a week of
stormy weather that will start late tonight. Be sure to clear
drainage areas, culverts and drains of debris and snow. We are
also recommending that if you have flood mitigation in place to go
ahead and just leave it out for the next week as we transition to
a wetter, more stormy weather pattern. Please secure outdoor
items and check fences and trees ahead of the winds forecast for
tonight as well.

Late tonight-Thursday: First storm in the series is still on track
to begin impacting the Sierra and western Nevada late tonight.
Upper level winds will increase significantly tonight with ridge
winds easily picking up to around 80-90 MPH by Thursday morning.
Model simulations continue to trend upwards with the wind forecast
for Thursday morning. Around 4 AM the models are showing the
potential for downslope winds to develop and potentially stick
around through much of the morning. Forecaster confidence is
medium for the duration of the downslope winds at this time, so we
just went ahead with a high wind watch to draw more attention to
the wind potential for tonight into tomorrow. Otherwise, it is
likely that the foothills of the eastern Sierra and wind prone
locations for far western NV and northeast CA will see a period
of strong winds in excess of 55 mph late tonight and Thursday.
Wind gusts could affect travel for high-profile vehicles between
Janesville and the Mammoth airport. Winds should begin to decrease
later in the day as the atmosphere destabilizes and allows some
spillover to work its way into the lee of the Sierra. Keep an eye
on trees and fencelines Thursday as saturated soils could make it
easier for them to topple over with these wind gusts.

Onset of precipitation appears to have slowed a bit, which is
probably why there is an increase in the wind speeds, especially
in the lee of the Sierra. Rain and snow will push into the Sierra
between 5-7 AM on Thursday morning, so expect slow downs on the
morning commute, especially if you are traveling across the higher
passes. Snow levels will start around 6500 to 7000 feet and will
fall slowly through the day. Timing of the heaviest precipitation
along the Sierra will be between 10am and 4pm on Thursday. Liquid
precipitation totals will be highest for northeastern CA and Tahoe
(0.5-1.0 inch). Snow levels will drop to around 5500 feet by late
Thursday afternoon, but most of the moisture will have moved out
of the region by then. This storm will bring additional snow
accumulations, especially to areas above 6500 feet. Up to a foot
of snow will be possible along the Sierra crest, with only a few
inches for areas below 6500 feet.

This system moves in quickly and is pretty much done by Thursday
evening, so the short duration of this event will limit storm
total precipitation amounts. Although we can`t rule out a short
period of moderate to locally heavy precipitation that could bring
some minor flooding concerns to areas already affected by recent
floods, including rivers in northeast CA (Pit, Susan, Middle Fork
Feather), and smaller creeks around the Tahoe basin. -Edan

.LONG TERM...Friday through Tuesday...
Only minor changes to the long term forecast with this forecast
cycle as recent model simulations have been fairly consistent with
the timing and intensity of the next series of storms.

The biggest forecast challenge with the first system (Friday into
early Saturday) is snow levels because it starts with a period of
southerly flow followed by only weak cold advection as the upper
trough moves across the region. Thus, forecast confidence is low
but snow levels are still expected to fluctuate between 5500-7000
feet. QPF is still expected in the 1-2 inch range along the
Sierra Crest with the highest amounts most likely in Mono and
Alpine Counties. Periods with travel restrictions above 6000 feet
are likely in the Sierra with this storm and with our deep
snowpack and wet soils, there is also potential for renewed
flooding impacts.

Showers could linger Saturday afternoon and Saturday night especially
in the Sierra, but overall a break between systems with a drying
trend is expected through Sunday evening.

The Sunday night through Monday night system looks to be have an
organized cold-frontal structure with better potential to be a
heavy snow producer. Latest model simulations continue to show
impressive ingredients including a 130+ knot southwest jet stream
over the Sierra, 50-70 knot 700 mb winds, moderate atmospheric
river, and a strong surface low off the Oregon Coast. Snow levels
could start above pass level with a strong cold front eventually
pushing them down to at least the western Nevada foothills.
Lowering snow levels could reduce the flood threat somewhat, but
again we can`t rule out renewed flooding issues. JCM

.AVIATION...

Increasing southerly flow sets up this afternoon with surface gusts
at terminals generally increasing into the 10-20 kt range. Late tonight
into Thursday winds aloft continue to increase and after about
12z Thursday there is potential for downslope winds in the lee of
the Sierra along with rotors and at least moderate turbulence.
Very strong surface winds with peak gusts over 60 kts are
possible in the Sierra and along the Sierra front range. Winds
should decrease after 00z Friday.

A stormy period with mountain obscuration and periods of IFR
conditions for Sierra terminals is expected 12z Thursday through
Saturday morning. Conditions should improve by Saturday afternoon
with a short break between storms and the next storm expected to
arrive late Sunday night. JCM

&&

.REV Watches/Warnings/Advisories...
NV...High Wind Watch from late tonight through Thursday afternoon
     NVZ002-003.

CA...High Wind Watch from late tonight through Thursday afternoon
     CAZ071>073.

&&

$$

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



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