We kicked off Mallory's Weather Blog with a story about El Nino and the effect it had on winters in the Shenandoah Valley. Almost a year later (can you believe it!?), we're talking about La Nina and the winter time. However, they deliver very different results.
When I put out my winter forecast a few weeks ago, I mentioned that we would likely see much lower total snowfall this year compared to last year. The National Weather Service in Sterling has provided us with details about previous snowfalls during La Nina years.
For the most part, La Nina years are below at or average concerning snowfall (average snowfall is about 25"). The one exception was the Blizzard of 1996, which occurred during a weak La Nina period and has essentially skewed averages of weak La Nina events. Temperatures stay at or slightly above seasonal averages.
In moderate to strong La Nina events (like the one we're going into for Winter 2010 -2011) we can except less than average snowfall (my prediction = 15") and temperatures just slightly above average. We'll still see storm systems come through the Ohio Valley and the East Coast, however the track of the low pressure determines our fate.
Low pressure tracked east of the Appalachians last year with our big storms, leaving us with plenty of cold air to tap into for snowstorms. This coming winter, we're anticipating low pressure tracking west of the Appalachians, keeping us on the warmer side of the system. A setup like that has two possible solutions. One, obviously, is rain. The other, if we happen to be influenced by cold air damming, would be ice. The track of our low pressure system makes or breaks our system - 30 miles to the east or west could change everything.
In conclusion, a La Nina winter doesn't mean that it will be boring, but by no means will we be seeing a repeat of last year.