Current (7pm eastern time) display the infamous shortwave just offshore the west coast of the North American Continent. In the next day, it will make its way onshore. There are many uncertainties about this shortwave ejecting east and how the Rocky Mountains will influence it. Historically speaking, the showtwave should move over the Rockies and "compress". On the right side (lee) side, vertical stretching of the atmosphere will induce cyclogenesis and a surface Low pressure will develop.
Obviously, since we won't know the exact track of the surface cyclone until it makes its way east of the Rockies, forecast models are all over the place with this system. Below are some thoughts by forecasters at the Buffalo, NY National Weather Service.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
...A Major Winter Storm With Significant Impacts Expected This
We will be in the midst of a major winter storm with significant
winter weather impacts on Sunday.
The winter storm will still be deepening on Sunday as it moves
off the New England coast. Steady snow continuing areawide
Sunday morning will shift away from the area during the day, as
we transition to the lake effect portion of the storm. The
coldest air this winter season will be drawn down into the
region on the backside of the storm and bring lake
enhanced/effect snows to the region through Sunday night. This
could bring significant additional snowfall totals, especially
to areas south and southeast of the lakes, including the
Rochester metro area. Strong northerly winds on the backside of
the storm will result in significant blowing and drifting snow
likely creating difficult if not impossible travel conditions in
many areas. Dangerously cold wind chills are also likely,
dropping to 15 to 25 below zero for most areas and perhaps as
cold as 30 to 40 below zero for the North Country.
The powerful winter storm will exit across the Canadian maritimes by
Monday, as a large arctic high crosses into the upper Midwest/Great
Lakes. A deep north to northwest flow between these features will
maintain a very cold north-northwest flow of air with 850 mb
temperatures nearing -26C. This brutally cold airmass will most
certainly support more lake effect snow showers, particularly
south and southeast of the lakes along with dangerously cold
Significant spread in long range model solutions exists for the
midweek time frame. Signal is evident for recovery of
temperatures to closer to normal values as the arctic air
departs Tuesday into wednesday, but the development of a trough
in the central CONUS is causing some issue. The Euro and GFS
both advertise low pressure developing and moving up the Ohio
Valley into the eastern Great Lakes, while the Canadian has a
clipper-type low swinging through the region. Timing differences
also exist between each solution, but the Wednesday time period
currently appears to be the best timing for the arrival of
precipitation from this system. Some warmer air gets pushed
northward toward the region on the southern end of the
precipitation shield, but for now will keep the precipitation
type as all snow until more consensus in guidance is achieved in
the coming days.
...WINTER STORM WATCH IN EFFECT FROM SATURDAY AFTERNOON THROUGH
* WHAT...Heavy snow possible. Light snow will begin as early as
Saturday morning. Snow will become heavy Saturday night and
continue into Sunday. Snow will then transition to lake effect
Sunday night and continue through Monday. At this time, greater
than 7 inches of snow is possible. Gusty winds and arctic air
will also produce blowing and drifting snow and wind chills well
* WHERE...All of western and north central New York.
* WHEN...From Saturday afternoon through Monday afternoon.
* ADDITIONAL DETAILS...Plan on slippery road conditions.
Widespread blowing snow could significantly reduce visibility.