Peter Hines

by Peter Hines
Webmaster and Contributor

Artic Oscillation Blamed for Snow Drought

By all accounts the 2010-2011 winter was epic when it came to skiing and riding. The snow started early, came consistently and continued into the spring. Huge amounts of snow existed in many of the western resorts with some remaining open into June. Some mountains even had a small "second season", where skiers and riders started up again after a brief hiatus.

This winter when I get up in the morning I look out at see the same drab brown grass in my yard. There is no snow. When snow comes, it has been meager and it doesn't last. It is usually gone in a day. In the Northeast we are on track for one of the driest snow years on record. We keep waiting for the "big dump" but it hasn't happened.

That doesn't mean that there hasn't been good days on the slopes. Snowmaking has saved the sport and season that so many of us love. This writer skied at Saddleback and Sugarloaf in mid February one good natural snow.

So what's the cause of this? Many weather experts are pointing to Artic Oscillation (AO). What is AO one might ask? Before you can understand AO you need to understand the Jet Stream which is a band of west to east blowing high altitude winds the circle the entire globe.

Jet Stream
Image Source: NASA

The jet stream effects winter weather because acts as a boundary between cold polar air and warmer topical air in the south. In essence if you are above the jet stream you are going to experience colder wintery weather and potentially more snow. If you are below the jet stream you are going to experience warmer drier weather.

This is what we have been experiencing in the lower 48 this season. Conversely some parts of Alaska have been getting dumped on with snow.

The prevailing westerly flow of the jet stream takes on a wavelike pattern composed of a series of ridges and troughs. When the jet stream bulges to the north a high pressure ridge is formed. When an area is under the influence of a "ridge", temperatures are generally warm and weather conditions fair, warm coms up from the south. When the jet stream bulges southward, a low pressure "trough" develops. When an area is under the influence of a trough, temperatures are cool and weather conditions cloudy or stormy. When there is neither, which is what we are experiencing, the weather are somewhat stagnant.

Ridges and Troughs

The low pressure trough are generally associated with snow storms in the winter. Also, the typical noreaster usually involves warm moist air traveling from southwest to northeast running into cold air from a jet stream trough resulting in significant amounts snow. This year moist air from the south has not run into cold air. This has resulted in several rain storms in the northeast.

Over most of the past century, the Arctic Oscillation alternated between its positive and negative phases. Starting in the 1970s the oscillation has trended to more of a positive phase when averaged using a 60-day running mean, though it has trended to a more neutral state in the last decade. The more positive direction in recent decades has led to lower than normal arctic air pressure and higher than normal temperatures in much of the United States and northern Eurasia.[6] Could this be an explanation for our general warmer weather? Winters haven't been like many of us remember.

Many ask if AO is the cause or the effect of global warming. The jury is out on this but many climatologists agree that the climate is not the same as it was in the past.

So what does this all mean? At least it is an explanation. There isn't much that we can do but hope for a trough, or several troughs, which give us more snow.

Regardless, there is snow on the mountains, albeit man made and some mountains have copious amounts of natural snow. Much of it is very good and the weather is warmer than in previous years. Artic Oscillation is a not reason to sit at home because there is no snow at your house and your grass is brown. Head to the slope and enjoy the outdoors and what is there.


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