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Where Did Winter Go?

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Prior to the second week of January, many of us have been wondering whether old man winter was going to make an appearance in the Sioux Empire this year. With record setting high temperatures and one of the latest first 1 inch snowfalls in South Dakota history it was easy to see why. During the second week of January, old man winter made his first appearance, bringing sub-zero temperatures and fresh snowfall. As we now near the end of January, above average temperatures and dry conditions have once again made their return to the Sioux Empire. On Monday, 90 percent of the continental United States will see temperatures above their average. Many of us have wondered just where winter has gone but the answer lies well to our north in our 49th state; Alaska.
Many towns in Alaska are on track to have the coldest and snowiest winters on record.

(Current Alaska Temperatures Monday Morning)

Fairbanks has experienced the coldest winter since 1971 as temperatures dipped well below zero. Just this morning the temperature in Fort Yukon dipped down to 65 degrees below zero. The cold and snowy winter caused a fuel shortage in the town of Nome, when an early season storm delayed a pre-winter fuel shipment. Soon Nome was iced in and desperately close to a fuel shortage. Gas prices jumped to $9 a gallon before Coast Guard ice breakers broke up enough ice to get a Russian tanker close enough to deliver fuel through a mile long hose. Who could forget the images of the small town of Cordova, which was buried in over 10 feet of snow. The National Guard is still there clearing the 172 inches of snow they have received since November.

(Cordova, Alaska)

(Cordova, Alaska in January 2012)

(Cordova, Alaska burried under 10 feet of snow)

Even in Anchorage, they have already doubled their average winter snowfall with 88 inches of snow. Portions of Canada, have also experienced one of the coldest winters in over 20 years.

(Current Canadian Temperatures Valid Monday Morning)

With most of the cold air in North America confined north of the Canadian border, the positive Arctic Oscillation for the first half of winter is a good explanation for the northern confinement.

The Arctic Oscillation is an index that explains the pattern of air masses in the mid to upper latitudes. The index is calculated on sea-level pressure differences over the north pole. When the Arctic Oscillation or “AO” for short is positive, winds around the north pole increase essentially locking cold air in place, not allowing cold air to spill out of the polar regions.

(Arctic Oscillation Image courtesy: J. Wallace University of Washington)

This winter the AO was highly positive up until the second week of January essentially trapping cold arctic air in the high latitudes allowing places like Alaska and Canada to experience extremely cold arctic air for long periods of time. When the AO index goes negative the gradient decreases allowing arctic air to plunge farther south. The AO index became negative around the second week of January, which allowed some of our coldest air all season here in the northern plains. This week, the northern plains will see more well above average temperatures and yet the AO is still very negative. This is where another index comes into play.

(Arctic Oscillation Forecast valid Jan. 30th)

The North Atlantic Oscillation or “NAO” as it’s commonly referred to is the second part of our cold weather puzzle. The NAO is an index very much like the Arctic Oscillation in that it measures differences in sea-level pressure. The NAO measures the strength of two very important areas: the Icelandic low and the Azores high. The NAO becomes positive when strengthening of the Icelandic low and the Azores high creates a large pressure gradient.

This gradient causes the westerly winds, which steer our weather patterns to strengthen. This strengthening of the westerlies allows cold air to drain faster off of North America by moving cold air to Europe. This generally creates warmer than average temperatures in the United States and colder weather for Europe. In contrast, a negative NAO causes weakening of the pressure gradient over the North Atlantic, allowing cold air to pool in North America and arctic air to surge south from Canada.

The NAO has been positive for the last week or two, and that has accounted for warmer than average temperatures in the United States despite a negative AO. If the cold air is drained from the U.S. it has to go somewhere right? Europe experiences greater cold air pooling during a positive NAO, as cold air rushes off of North America and pools in Eastern Europe. A positive NAO would explain the current deep freeze Eastern Europe is experiencing.

(NAO Forecast valid Jan. 30th)

Eastern Europe has been in a deep freeze for over a week resulting in 32 deaths attributed to hypothermia. Temperatures dropped Monday morning to 15 below zero in Poland, warming up from the previous nights 27 degrees below zero. The cold weather and snowfall, stranded many motorists in the mountain regions and caused the closure of London’s Gatwick airport for two days.

90 percent of the United States will see afternoon high temperatures well above normal

(Forecasted High Temperatures well above average Monday)

The warm weather and dry conditions will only lead to a larger deficit to snowfall this year, especially in Sioux Falls where snowfall is two feet below average.

(Sioux Falls 2011-2012 Winter Snowfall)

(Pierre 2011-2012 Winter Snowfall)

The warm and dry trend will continue through the weekend, where a potential storm Friday could bring a chance for some rain/snow to our southeastern areas. Until then, it looks like we won't be adding many more days below freezing days.

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