Northern Plains Heavy Snow: 9-10 November 2012

Over the next couple days, a major winter storm will exit the northern Rockies and move into the northern Plains. Numerous winter storm watches and warnings are in effect from now through 10 November (see image below).

After a couple of runs when the domain selection algorithm did not accurately capture the center of the system exiting the Rockies (FWIW this issue should be ironed out now), this morning's analog runs have.

The COOP snowfall guidance from the analogs based on the 8 November 2012 1200 UTC 48-h forecast has moderate probabilities for > 6" of snowfall (image below) from MT and northern WY into northwestern SD and most of ND. This is very similar to where the NWS Winter Storm Watches and Warnings are currently in effect for this area (CO mountains as well).

One of the more similar analogs to the forecast is 8 October 1985. Shown below is the classic 4-panel loop from the NAM forecast (top) and November 1985 analog (bottom).

Although the strength and patterns of the surface low, 850-mb circulation, midlevel trough, and upper-level jet interaction are remarkably similar in both analogs, what is important on where the snow swath sets up is the track of these features. The 850-mb lows both track from southeastern WY and western NE northwestward to eastern SD and then across northern MN. To fully analyze the similarities and differences between this analog and the forecast it is encouraged to use the link above. The widespread heavy snowfall that occurred with this analog extended from MT to ND where a large area of >8" fell within an embedded >12" band (below).

Furthermore, 8 October 1985 is statistically the most similar historical analog when the 72-h forecast is used to find similar historical events.