NWS Reno, NV wrote its last area forecast discussion before the first event at Jan 6, 8:43 PM PST, 5 hours 47 minutes earlier.
Area forecast discussion, Jan 6, 8:43 PM PST, 5 hours 47 minutes before
Area Forecast Discussion
National Weather Service Reno NV
843 PM PST Fri Jan 6 2017
.UPDATE...
Limited changes to tonight's forecast. Mid/high clouds are
starting to move into the area and that should stem the downward
trend on temperatures overnight. Some areas may hit their lows in
the next couple of hours before leveling off or even starting to
rebound. The next storm system is on track to begin pushing into
the region Saturday morning. Some model simulations show pcpn
developing a little slower...but it is not enough to make big
changes to the forecast.
Forecast soundings still point toward the lower valleys of eastern
California and western Nevada starting as snow but then warm air
aloft creates a situation where a period of freezing rain
develops. The far northern valleys from around Cedarville south
and east into the Gerlach area and northwest Pershing County are
far more likely to see a prolonged period of snow mixed with
freezing rain. It is less likely for areas from
Reno/Fernley/Fallon south...but not out of the question from
around 9 am to just after noon Saturday. By mid afternoon most of
these areas should have just rain.
Will leave the Winter Weather Advisories as is for now. We can
make adjustments as needed Saturday.
Flood potential still looks very good as snow levels climb above
8000 feet by late Saturday and rise into early Sunday afternoon.
Farther south into the Mammoth area...the snow levels could reach
between 9500 and 10,000 feet late Sunday before falling into
Monday. Small streams are at risk for flooding throughout Mono
County below about 8500 feet. 20
&&
.PREVIOUS DISCUSSION... /Issued 320 PM PST Fri Jan 6 2017/
SYNOPSIS...
A strong atmospheric river storm is still on tap for this weekend
bringing copious amounts of rain and snow to the region Saturday
through Monday. Significant flooding is expected mainstem rivers,
creeks, and streams Sunday into Monday. Another atmospheric river
event is looking likely for the middle of next week with a couple
of colder storms to follow the end of next week.
SHORT TERM...
* Strong Atmospheric River likely Saturday through Monday
* Flooding expected Sunday-Monday. Prepare Now!
* Freezing rain possible in valleys below 5500 feet Saturday.
* Poor conditions for travel and outdoor activities this weekend.
Moisture and warm air advection will increase across the region
late Friday night into Saturday morning. Current forecast
simulations are showing southwest flow aloft, while surface winds
remain NE-E. With plenty of cold air trapped at the surface, this
can be a classic scenario for freezing rain, especially for
valleys below 5500 feet. The valleys most at risk are those in
northern Washoe and Pershing counties where the freezing rain
potential will exist through Saturday night. Other locations are
likely to see snow or a wintry mix as thermal profiles go
isothermal before changing to rain. Mountain locations will see 6
to 12 inches of additional snow before snow levels rapidly rise
Saturday into Saturday night. Widespread travel impacts are
possible due to snow and ice covered roads late tonight into
Saturday morning throughout the Sierra and northwest Nevada.
Snow levels should rise rather quickly Saturday afternoon/evening
as deeper moisture and warmer air arrives. Snow levels are
forecast to peak by early Sunday morning, then remain steady
through Sunday night. This will coincide with the most intense
precipitation. North of I-80 we're looking at snow levels near
8000 feet, near 9000 feet for Reno-Carson-Tahoe, and 9000-10000
feet south of US-50 including Mono County. Snow levels look to
gradually come down Monday morning into the early afternoon, but
latest guidance is not a sharp with the cold front as previous
model runs. With the lowering snow levels, snow is expected to
impact travel across all Sierra passes by midday Monday, possibly
even into western Nevada valleys by Monday night.
Liquid totals along the Sierra Crest through the foothills west
of US-395 could easily reach 6 to 12 inches over the course of
the event. Along US-395, rain totals could reach 3 inches with up
to 2 inches possible for areas to the east. Snow totals above the
snow line could easily reach 3 to 8 feet with the character of the
snow being very heavy and wet. Avalanche danger is likely to
increase through the weekend with backcountry activities not
recommended.
As far as winds, they will be strong and gusty across ridge lines,
with gusts peaking over 100 mph. Lower down, winds are not
anticipated to be as strong with gusts mainly in the 20 to 30 mph
range at most. However, a few periodic stronger gusts are
possible, especially on Sunday.
The biggest takeaway is this: We know that it will flood on Sunday
into Monday. The time to prepare is now before the storm begins to
move into the region on Saturday. -Dawn
LONG TERM...Tuesday through Friday...
Impressive wet pattern along the west coast continues into next
week. The persistent blocking pattern in the Bering Sea will keep a
large scale low pressure system locked in the Gulf of Alaska with
the Pacific jet pointed at the California through most of next week.
Moist onshore flow will keep the Sierra in almost continuous
precipitation pattern through much of the next week.
Not much of break is expected between storms as the next significant
system arrives on Tuesday when jet stream draws another Atmospheric
River into the Sierra. The major difference with this storm compared
to the weekend event is that jet stream will be further south
allowing colder air into the region. Snow levels with this system
are currently projected to be in the 5000-7000 foot range. The lower
snow levels should keep flooding concerns to lower elevation creeks
and streams. However, if the snow level forecast go higher flooding
could again be a concern. For this reason we recommend keeping any
flood mitigation plans in place for the start of next week.
Additional snow amounts of 2-5 feet are possible with this system
with the highest amounts currently expected to be in the central
Sierra.
Additional storms will be possible at the end of the week, however
the jet stream starts become more variable at that point with
fluctuations in storm track forecasts likely for the end of the
week. -Zach
AVIATION...
Mainly VFR conditions exist across the area this afternoon with
mid and high level clouds beginning to increase ahead of an
approaching system. A few lingering lower level clouds are
obscuring terrain around the region, but these are continuing to
scatter out.
Snow will begin in the Sierra early Saturday morning, spreading
into western Nevada. 4 to 10 inches of accumulation is likely on
runways at KMMH, KTVL, and KTRK through Saturday afternoon.
Accumulation in western Nevada will be more limited, likely 2
inches or less for KRNO and KCXP. The other concern on Saturday is
a chance for freezing rain, especially in colder valleys of
western Nevada in northern Washoe County and Pershing County.
This will transition to heavy rain, torrential in the Sierra and
the Sierra foothills, by Saturday night into Sunday morning.
Widespread MVFR-IFR conditions and mountain obscuration is likely.
This heavy rain will lead to flooding issues and ponding of water
on runways. For KRNO, it is possible that Steamboat Creek may
back up and cause some flooding along the south end of the
Airport.
Snow levels will fall on the other side of the system with
accumulating snow once again possible at Sierra terminals by
midday Monday. -Dawn
HYDROLOGY...
* High confidence in flood impacts similar to the flood of December
31, 2005 along the Susan, Middle Fork Feather, Truckee, Carson,
West Fork Walker and their tributaries.
* High risk for flooding near creeks, streams, urban areas, and
farmland and burn scars.
* Flood preparations should be completed by Saturday afternoon.
* Intense rain arrives Sunday and Sunday night.
Well advertised atmospheric river will move into the region Saturday
with a period of intense rain and high snow levels from late
Saturday night to Monday morning. Hourly rainfall rates should
exceed 0.50 in/hr at times in the Sierra/Carson Ranges Sunday and
Sunday night. Snow levels will lower on Monday near the end of the
event which will end the flood threat in the mountains, though high
flows on the main stem rivers will continue into Tuesday.
Soils are saturated and based on the response of rivers, creeks,
streams and drainage ditches Wednesday, it won't take much rainfall
to generate flood impacts across the Sierra and western Nevada.
Creeks, streams, urban areas and farmland are at high risk for
flooding late this weekend. Washoe Valley and the Little Valley
burn scar are also likely to have flooding from this event.
Total rainfall amounts from Saturday night through Monday still look
on track with 6-12 inches for areas west of Highway 395 including
Mono County, the Tahoe Basin, Lassen County, Plumas County, the
Carson Range and Reno/Carson City foothills. Farther east in the
lower valleys, 2-4" are possible with 1-2" for the highway 95
corridor.
Peak flows are forecast to hit late Sunday afternoon and night for
the Susan, Truckee above Derby Dam, Carson system above Carson City.
Peak flows in the lower reaches of the Truckee, Carson and Middle
Fork of the Feather in Portola should hold off until Monday into
Tuesday as the water drains through the systems.
The recent 4-8 feet of snow in the higher elevations of the Sierra
will play a role by initially absorbing quite a bit of rain with
some melt off possible. Another factor to add to the mix is the
recent snow at elevations below 6000-7000 feet plus the any
additional snow with the initial phase of the system on Saturday
that will melt and run off. Something to keep an eye on, as how this
plays out could impact the severity of the flood impacts. Brong
&&
.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 4 AM Saturday to 4 AM PST Sunday
NVZ004-005.
Flood Watch from late Saturday night through Monday afternoon
NVZ002-003.
Winter Weather Advisory from 4 AM to 10 PM PST Saturday NVZ002.
Winter Weather Advisory from 4 AM to 4 PM PST Saturday NVZ003.
Flood Watch from late Sunday night through Tuesday afternoon
NVZ004.
CA...Flood Watch from Saturday evening through late Sunday night
CAZ071.
Winter Weather Advisory from 4 AM Saturday to 4 AM PST Sunday
CAZ071.
Winter Weather Advisory from 4 AM Saturday to 4 AM PST Sunday
CAZ070.
Flood Watch from late Saturday night through Monday morning
CAZ073.
Flood Watch from late Saturday night through Monday afternoon
CAZ072.
Winter Weather Advisory from 4 AM to 10 PM PST Saturday CAZ072.
&&
For more information from the National Weather Service visit...
http://weather.gov/reno