Scientific Forecaster Discussion
fxus65 krev 172255
Area forecast discussion
National Weather Service Reno Nevada
255 PM PST sun Nov 17 2019
The quiet and persistent weather pattern will last another day
before coming to an end on Tuesday as high pressure weakens. A low
pressure system looks to drop south Tuesday evening through late
Wednesday bringing light valley rain and high elevation snow to
areas mainly south of Highway 50. The tranquil weather returns for
the end of the week with high pressure building in once again.
The tranquil weather conditions with warm afternoon temperatures
continues for the rest of today through Monday as high pressure
dominates the West Coast. As Tuesday arrives, the weather pattern
begins to change with the ridge moving off to the east making way
for a low pressure trough to drop south from the Pacific northwest.
Cloud cover and westerly winds increase ahead of the trough Tuesday
morning before winds switch to the north as the associated cold
front pushes through by late afternoon. Winds are not expected to
be too strong with this frontal passage (gusts of up to 35 mph in
wind prone locations), but nonetheless may cause minor issues for
air travel. See the aviation discussion below.
Once the front makes its way through the region dropping snow
levels to ~6000 ft, a deformation band of precipitation looks
likely to set up along the I-80 corridor from Winnemucca to the
Tahoe basin southward Tuesday night lasting through Wednesday
morning. During this time, areas along I-80 are forecast to see
light rain showers as elevations above 6500-7000 feet could see a
light snowfall with a few tenths of an inch of accumulation,
including Virginia City and South Lake Tahoe. Mount Rose and
Carson Pass could even see up to an inch of new snowfall.
As the low pressure system digs into Southern California/Nevada by
Wednesday morning, precipitation chances increase for areas south
of Hwy 50 due to wrap-around moisture and upslope flow, particularly
in Mono County. Recent model guidance continues to show most of
the moisture from ts Raymond to be pushed too far southeast over
central Arizona, indicating that we will not be tapping into the
bulk of that moisture source. Having said that, with the tropical
moisture too far east colder air will be allowed to move through
our region lowering snow levels enough to see a light snow
accumulation for elevations above 6500 ft. More concerned about
the Sierra passes at this time with 2 to 4 inches of total
snowfall possible for ebbetts, Sonora, and Tioga by Wednesday
evening. Hazardous driving conditions are likely on these roads
during this time.
Temperatures on Wednesday will be quite chilly with highs only in
the low to mid 40s and overnight lows in the 20s region-wide.
Precipitation diminishes early Thursday morning as the low,
centered over southern Nevada, shifts to the east allowing high
pressure to build back in once again. -LaGuardia
Long term...Thursday night into Thanksgiving week...
High pressure builds back over the region Thursday night through at
least Saturday. This will bring Back Valley inversions and light
winds, with temperatures remaining around average for valleys
(highs 40s and 50s with lows teens and 20s).
Next Sunday into Monday, a system could drop into Pacific northwest
and intermountain west. Many ensembles appear to keep the wave north
and east of the region with just a glancing shot at showers north of
I-80. However, a few runs of the GFS drop a slider-type system into
the region for a better shot at Lower Valley rain and snow showers
and foothill/mountain snow showers. At this time the slider solution
is less probable but bears watching.
Looking well ahead toward Thanksgiving, ensemble systems are hinting
at another wave for Nov 27-28. Doesn't look like a big system at
this time but it doesn't take much to impact Holiday travel.
Monday should be the last day of light winds along with VFR
conditions. As we move into Tuesday an upper level area of low
pressure will begin to drop south into the region. Ahead of this
low winds aloft will begin to increase with gusts increasing to
30-40 kts over the Sierra ridges. This should lead to increased
chances for turbulence aloft but little in the way of low level
The upper level low will continue to drop south and interact with
moisture being pulled north by early Wednesday. This sets up a
scenario where showers develop from the Sierra eastward into the
basin and range country. The best chance for widespread light to
moderate precipitation is south of Highway 50...but isolated
showers are possible as far north of Interstate 80 Wednesday into
For areas south of Highway 50...especially mountainous areas...
conditions will begin to deteriorate late Tuesday night with
occasional MVFR/IFR conditions possible through Thursday afternoon.
Lowering snow levels will mean increased chances for icing and
intermittent periods of moderate to heavy precipitation and low
clouds will likely produce widespread mountain obscurations.
By next weekend conditions begin to improve with far better flying