Scientific Forecaster Discussion
fxus65 krev 221118
Area forecast discussion
National Weather Service Reno Nevada
318 am PST Wed Feb 22 2017
Bands of snow moving across the Sierra and western Nevada will
produce hazardous driving conditions for this morning's commute.
Lighter snow showers will linger through Thursday with cold
conditions for the next few days. Another storm may bring
widespread snow even to some valleys later this weekend into
early next week.
Even though model guidance has been trying to diminish snow during
the overnight hours, convective snow bands have persisted across
the Sierra and most of eastern California-western Nevada from US-50 northward.
Outside of the Sierra where several feet of snow have accumulated
since early Monday, many of the northern and western foothills
around Reno (including the National Weather Service Reno office) have been slammed with
snowfall totals surpassing 1 foot. Even in lower elevations
around Reno-Sparks where snow has taken longer to stick, a few
inches have accumulated since Tuesday evening. Snowfall totals
near and south of US-50 including Carson City and Minden, and
across west central Nevada have generally been much lower. Even if
the snow does taper off during the next few hours, temperatures
near or below freezing will increase the risk of patchy black ice
forming on roads that may currently be wet. We will extend all
active winter weather headlines through 10 am this morning as
these areas will see hazardous travel conditions through the
morning commute from either icy or snow covered roads, along with
reduced visibility in snow and/or fog. Blowing snow may also be
encountered in areas where winds kick up today, as most of the
snow that fell overnight is much more powder-like compared to the
heavy wet snow that fell during the day Tuesday.
Among all of the records this extreme winter has produced so far,
the Reno Airport has just surpassed the record for total water
year precipitation (12.73 inches since October 1) since the
Airport has existed. There are more than 7 months left so any
additional rain or snow will just Widen the distance between 2017
and the previous Airport record from 1983.
After the convective snow bands diminish this morning, chilly and
unsettled conditions will continue today through Thursday as weak
disturbances within cold northwest flow aloft will keep the
chance for light snow showers going at times. The best chances
this afternoon and evening appear to set up north of I-80. Later
tonight into Thursday morning, colder air aloft moving over
relatively mild temperatures over area lakes (especially pyramid
lake) with unstable air mass could lead to some bands of snow
forming along and southeast of the main lakes. Forecasting the
magnitude and location of lake effect snow bands is quite
difficult, but a few locations could receive at least a couple
inches of snowfall if these bands persist over the same location.
Anyone traveling on I-80 near and east of Fernley Thursday morning
could encounter rapid drops in visibility with slick roads. Then
by Thursday afternoon, snow showers look to increase in coverage
again along the Sierra and much of western Nevada. With the exception
of isolated locations where heavier snow bands persist, most areas
will receive additional snowfall of 1 inch or less.
Thursday night through Friday night should be mostly dry as more
stable air mass with limited moisture moves overhead. The only
possible exception may be in portions of northeast California and far
northwest Nevada where another weak shortwave could trigger a few very
light snow showers. By this time, the main weather highlight will
be even colder temperatures Thursday night, with lows mainly in
the teens, while colder Sierra valleys and locations with
significant snow cover could see lows in the single digits or
below zero. Mjd
Long term...Saturday through Tuesday...
The only significant changes made to the extended forecast were to
increase pops and quantitative precipitation forecast again for the late Sunday into Monday time
frame. The operational models are not in quite as good agreement
this cycle as 24 hours ago...but there is still a very good signal
that this next system will be wet and cold...at least west of
The models try to bring a little quantitative precipitation forecast into the region Saturday but
both the European model (ecmwf) and GFS have the first part of the weekend/early next
week storm offshore saturday; the GFS is much farther west. This
will keep the best chances for pcpn well west of the region
Saturday into Saturday night. By Sunday the European model (ecmwf) has reverted
back to more of an open wave that moves through the region by
morning and a secondary low dropping south late in the day. The
GFS now has the first closed low lifting east-northeast across
northern California during the day Sunday and another low trying
to phase with the first one by Monday morning.
While the two operational models are diverging in their
solutions...most of the gefs ensemble members are now favoring a
solution closer to the GFS. That's not surprising given the
underlying physics of the models...but does lend a bit more support
to a solution like the GFS. So...while the actual solution may
differ from the current depiction...we will trend the forecast a
little wetter. We will also start to trend the snow levels a
little higher for Sunday...but still low enough for snow down to
most valley floors. A more over water trajectory early on and a
prolonged period of southwest flow aloft ahead of the main trough
that does not move through before Monday night will allow for a
better tap into a developing moisture plume moving out of the
eastern Pacific. This will aid in quantitative precipitation forecast production. We have
increased snow amounts such that it is likely we will need winter
storm warnings for all but the basin and range. Currently
constituted forecast has 6 to 10 inches of snow in the western
Nevada and eastern California valleys with 1 to 2 feet near Lake
Tahoe and Mammoth Lakes. The crest could see another 2 to 3 feet.
This solution is still very changeable given the model
A decrease to showers is expected by Tuesday as the main upper
trough passes to the south. Temperatures stay below average through
Snow showers linger through today and into the early evening hours
with IFR/MVFR conditions at times. Not all locations will see
showers...but many areas north of Highway 50 will until the main
upper level trough passes through the region Thursday morning.
Another inch or two of accumulation is possible at the Sierra
terminals today, while the lower elevation terminals see only
very minor accumulations of less than an inch this morning before
temperatures warm enough for just wet conditions.
A few snow showers are possible into Thursday...but these will be
more isolated in nature. By Thursday mainly VFR/MVFR conditions are
expected with rare instances of IFR in the heavier showers.
Winds are not expected to be as strong today either at the surface
or aloft. There is still likely to be some light turbulence but
widespread moderate turbulence is not as likely.
Flying conditions improve by Friday but then start to deteriorate
again later this weekend as another storm system buffets the region.
Nevada...Winter Storm Warning until 10 am PST this morning nvz002.
Winter Weather Advisory until 10 am PST this morning nvz003.
California...Winter Weather Advisory until 10 am PST this morning caz071.
Winter Storm Warning until 10 am PST this morning caz073.
Winter Storm Warning until 10 am PST this morning caz072.