We’ve had a snowfall forecast going on this year amongst a small group of us, following a pretty spot-on ensemble forecast for snowfall last year and the canonical La Nina year. The La Nina currently in the Pacific persuaded all of this years forecasts for snowfall in Moscow and Boise, Idaho to be above normal and conspicuously close to a composite, or normal, La Nina winter. No dice on seeing that “normal” La Nina winter come to fruition this year so far.
Although snow is currently falling in Moscow Idaho, the seasonal total stands currently at about 35″ in Moscow, and a measly 5.5″ in Boise for the water year. Applying the sort of statistics used during a baseball season to “project” the number of home runs a player should hit over 162 games, using the past as a guide to the future [not a good rule, but illustrative for our purposes], we can hone in on a statistical projection of WY 2011-12 snowfall for Moscow and Boise as below normal and far below a typical La Nina year. You can also see that if this was Price is Right, all forecasts this year would be overdone.
While there is still a significant chunk of the rainy season ahead of us, especially if we consider our short-term memory of the past two extended springs, the snowfall season for much of the lower elevations of the inland northwest is quickly closing.
I provide a map of the average percent of water-year snowfall observed at USHCN stations in the lower 48 prior to February 12th. Note that I only included stations that climatologically receive at least 10″ of snow on a calendar basis. It is pretty easy to observed a hot-spot in the PNW, indicating that around 80-90% of snowfall accumulation at COOP (mainly valley) stations in the PNW falls prior to February 12th. This reinforces the concept of the window for snowfall accumulation, at least at lower elevations, is quickly closing.
Moreover, by March 1st, a few weeks from now, that window closes further. Climatologically, Moscow – Spokane – Coeur d’Alene average 3-5″ of snow post March 1st, although locations in western Montana which tend to be cooler and have a more dominant spring precipitation signal can still accumulate after March 1st. It’s crunch time for western snowfall.