Where Is Winter????

We are several days out from February which can bring in some nasty cold spells and blinding snowstorms. However, the 2011-2012 edition of winter has been anything but that. Ski resorts are hurting in the Rockies as well as the Appalachians. In the Northeast, the white ground following a snowfall is quickly erased by either a rain storm or warm air. La-Nina has had it hand in all of this, but one of the biggest factors in our "spring-like" winter can be pointed to the NAO, or the North Atlantic Oscillation.

Take a few seconds and glean at the following image. These are temperatures across the U.S. as of 4pm CST, on this Friday, January 27th.

Yes, there is a noticeable difference in temperatures from the southern tier of the U.S. to the northern half. On the other hand, areas such as Billings, or even Boston are saying, "Hey, this is not so bad. We can go out with t-shirts on." Additionally, if you have closely been following the weather this winter season, any cold spell has been brief and there have not been many of them.

The main reason, the NAO (North Atlantic Oscillation). This is a weather phenomenon that was discovered in the 1920's. Therefore, we have not been observing this for long, but every year that passes we gain a better understanding on what is can do to our weather.

Main points to know here is that the NAO is an oscillation between the position and strength of a body of low-pressure around Iceland, as well as a body of high-pressure in the Azores. When talking about the strength of pressures, wind will be a factor. If there is a large difference between these pressures, then wind speed will increase. On the flip side, if the differences are small, wind speeds will be decreased. Finally, when talking about the winds with the NAO, we are talking about winds in the upper levels of the atmosphere.

There is a positive and negative phase to the NAO. During the positive phase, the pressure differences between the Azores High and Icelandic Low are vastly different. Therefore, the winds in the upper levels of the atmosphere over the United States are stronger than average. Due to these strong upper level winds, cold air built up at the surface in northern Canada will not have an easy time heading south. Therefore, cold spells will not happen that often and they will not last long, just like this winter.

During the negative phase, the exact opposite happens. Pressure differences are smaller, and the winds in the upper levels are weaker. Therefore, cold air locked up in Canada will be able to freely shuttle south and stick around for a while. The next image can give you an indication of what each phase looks like.

Image taken from Wikipedia

The tough part about this phenomenon is that we can only forecast this well only about two weeks out. Despite long term seasonal forecasting, the NAO and its sister the AO  (Arctic Oscillation) can be wild cards.

Just to give you a frame of reference in how warm its been across the US this month: Boston is about 5.2° above average, Rexburg Idaho is about 7.0° above average, and International Falls (one of the coldest places in the US) Minnesota is approximately 9.9° above average. These are quite impressive numbers. However, February is a new month, and with a new month could come some new weather. We will keep you posted here on KAGS-HD.

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