FOX44 - Burlington / Plattsburgh News, Weather & Sports12.29.11 Orographic Fun!

12.29.11 Orographic Fun!

"So...what gives with the snow?", you might ask. Well let me help you understand why some parts our region had near blizzard conditions, nearly a foot of snow, resulting in a shut down of parts of interstate 89...while other areas were sitting under nothing but clouds and bone dry.

Around northern New England and northern New York, we have mountains, simply put. The terrain in our area is what 1) makes weather seem so wacky from one town to the next and 2) keeps my job so interesting/frustrating. I really do enjoy forecasting for our mountainous terrain, but it does make pinpointing a forecast more challenging. Its difficult to make a forecast that calls for "anywhere from 0 to 13-inches of snowfall". But that is such a common occurrence around our area, and it's all about the terrain... 

The rolling terrain in our region influences the weather quite frequently. If you're an avid weather watcher, you probably know this. In yesterday's instance, the mountains helped enhance snow amounts, a process called orographic snow. Orographic snow is caused by a couple of essential ingredients..you need plenty of cold, moist air in the lower levels of the atmosphere very near the surface. The second ingredient is strong winds moving perpendicular (or nearly perpendicular) to the mountains. As the wind blows across the mountain barrier, air is forced upward. This lifting cools and condenses the air (which, remember needs to hold sufficient moisture). As the air condenses, it forms a cloud and eventually snow develops. Here it is interpreted with my awesome Microsoft paint skills....   

In our instance yesterday, winds were west-northwesterly, and with the north-south running ridgeline of the Green Mountains...voila! Snow!  The mountains essentially blocked that wind flow and squeezed out all the atmospheric moisture over those windward facing slopes.  The highest totals were found in eastern Chittenden and Addison county, as well as western Washington county in Vermont.

New Yorkers, the Adirondack mountains are not as susceptible to orographic snowfall as the mountains are more of a cluster, rather than the wall/line of mountains. While snow totals still tend to be enhanced by the high peaks, the effects are not as widespread, nor as populated as along the west facing (or in this case the upslope) sides.