Scientific Forecaster Discussion
fxus65 krev 101130
Area forecast discussion
National Weather Service Reno Nevada
330 am PST Tue Dec 10 2019
High pressure remains in place today, but a weak incoming weather
system may bring very light snow showers to the mountains this
evening into wednesday; little accumulation is expected. A
stronger weather system could impact the region by the end of the
week into the weekend.
High pressure will provide one more day of light winds, inversions,
and reduced ventilation in the lower valleys (below about 6,500').
There will be changes through the day however as an incoming weak
low pressure system passes through the region tonight into early
For today, this low will increase high clouds, strengthen Sierra
Ridgetop winds, and provide very light mountain snow and valley
rain showers tonight. Sierra Ridgetop gusts of 40-50 mph will be
possible by mid-afternoon as the low approaches and then peak this
evening with gusts up to 50-60 mph.
Precipitation will be light with generally a dusting of snowfall
across Sierra with about 30% probability of accumulating 1 inch of
snowfall on the Tahoe basin passes through early Wednesday morning.
The main window for seeing some light snow showers across Donner
Summit on I-80 generally looking about 10pm-4am, about an hour later
across Echo Summit on Highway 50, and after midnight through Mono
County. Although only light snowfall is expected, this still can be
impactful to trans-Sierra traffic with slick and icy conditions.
Across western Nevada valleys, a few hundredths of an inch of light
rainfall will be possible through early Wednesday morning.
Sierra ridgetops remain moderately gusty on Wednesday with breezy
winds reaching into the lower valleys Thursday result in better
mixing and ventilation. This will yield mild temperatures by mid-
December standards with valleys reaching the mid to high 50s. Winds
will begin to increase again early Thursday morning for the Sierra
ridges as the next storm approaches. Light precipitation is possible
across the Sierra crest from about Alpine County northward and
across far northeast California near the Oregon border. Snow levels
will be quite high, so should see mainly light rainfall below
7500-8000 through late Thursday into early Friday morning.
Long term...Friday Onward...
Friday will be quite mild for mid-December as we are on the warm
side of the jet stream with a weak plume of atmospheric river
moisture directed into the Pacific northwest. Northeast California
and northern Nevada will be on the southern end of this moisture
plume, but it will be enough to bring light rain and very high
elevation snow (8000-9000 feet) to the region on Friday.
How the remainder of the system progresses over the weekend has been
varying in scenarios. What we know is a cold front will drift south
by Saturday/Saturday night dropping snow levels potentially to all
valley floors. There will also likely be a period of enhanced
precipitation rates with the front, but it's a quick shot, which
would limit totals. The uncertainty lies in snowfall as the cold air
will be chasing the exiting moisture. Some scenarios would lead to
light accumulations on valley floors, but more likely is that
accumulations would remain above 5000 feet. There is another
shortwave that follows on Sunday, which could lead to one more round
of light snow at most all elevations. Once again, there is a spread
on snow amounts from nothing at all to several inches. The three
parts of the storm are unlikely to yield significant liquid totals,
however, travel impacts are certainly likely, especially Saturday
Following this system, the forecast gets quiet for a few days, but
the flow remains progressive (i.E. Stagnant conditions not
expected). Ensemble guidance is hinting at chances for another storm
around Dec 19-21, with general troughiness and storm chances
continuing into the days leading up to Christmas. This agrees with
the CPC 8-14 day outlook which favors below normal temperatures and
above average chances for precipitation during the timeframe.
Christmas travel may be impacted, especially given murphy's law. No
need to freakout yet, but be sure to check back if you have travel
Dense fog remains in place in the Martis Valley, including ktrk. The
question today is if we'll see the valley mix out enough to erode
the fog layer. Mixing is rather limited early today, but winds will
be increasing aloft ahead of a weak wave that will pass through the
region tonight. Forecast soundings are showing drier air aloft also
eroding the stratus deck, so there is a 75% chance we'll see
clearing at ktrk by mid morning or early afternoon.
A weak system moves in tonight into Wednesday bringing light rain
and snow along with the return of lower ceilings obscuring terrain.
This system is likely to keep fog from returning to ktrk most of
tonight, but if skies clear fast enough, early morning fog is still
possible. Runways in the Sierra could see a dusting of snow tonight.
Winds across Sierra ridges are likely to peak this evening in the
50-65 kt range, leading to turbulence along and downwind of the