"It's warmer this year mainly because of the jet stream pattern," said AccuWeather.com Senior Meteorologist Michael Pigott. "Generally, for the most part of the winter, it has been on a west-to-east pattern. Meteorologists refer to this as a 'zonal flow.' Essentially, we've seen a lot of storms moving from west to east, and not a lot traveling northward or southward. So, anything in the Arctic is staying up there, and anything in the U.S. is staying put as well. If you have north-to-south undulations in the jet stream, you do get warmer air heading northward to the poles, and colder air comes down toward the U.S. from the Arctic."
Nine states recorded their top ten warmest average temperatures for January in 2012: Wyoming, North Dakota, South Dakota, Oklahoma, Nebraska, Missouri, Minnesota, Arizona and Kansas.
It has also been the fifth-warmest, six-month period from August 2011 to January 2012 ever recorded in the contiguous U.S. Forty states have had warmer-than-average temperatures.
Alaska Would Beg to Differ
Even though the contiguous U.S. has seen record warmth this winter, Alaska is a different story. Several towns in Alaska have seen their coldest January on record.
Pigott continued, "Since the jet stream isn't moving colder air southward, it's getting trapped over Alaska. It's basically creating an extreme divide in record temperatures there compared to the rest of the U.S."
Nome, Alaska, has experienced their coldest average January temperature ever recorded with a frigid 16.6° below zero. Other bone-chilling Alaskan lows occurred in Bethel with 17.3° below zero, McGrath with 28.5° below zero and Bettles with 35.6° below zero.
Precipitation Across the Nation
In addition to a warm January in 2012, it has also been dry. In fact, the contiguous U.S. has seen its 28th-driest January in recorded history. The central Plains had below-average precipitation for the month, especially in Kansas. Kansas had its third-driest January in recorded history, while Nebraska saw its eighth-driest January.
"One reason the central Plains have seen less-than-average precipitation has been due to the weakening of storms coming from the West," said Pigott. "When these storms hit the Rockies, they tend to stall out and weaken in intensity."
However, this has not been the case for every state. Texas has actually seen above-average precipitation for the second month in a row. The state had not had two consecutive months of above-average precipitation since January-February 2010.
If March Comes in Like a Lamb...
The warm trend may continue through the end of February and into March, but temperatures are not expected to be as high as they were in January.
"It looks like the pattern will be similar for most of the country, but not to the same extent," said AccuWeather.com Expert Senior Meteorologist Jack Boston. "We are getting in a pattern where we're more susceptible to cold air masses coming down. However, that doesn't mean they're going to stay. They're still going to be progressive. That means cooler temperatures will come in for only a few days, then disappear again."
Intermittent stretches of cooler air will bring overall average temperatures closer to normal for the months ahead.
"The average will be somewhat above normal, though it won't be as above normal as January. But, it will be closer to normal," added Boston.
Boston also stated that he thinks temperatures in the Northeast will begin to drop "just in time for spring."
"Unfortunately, I can see a pattern developing where we will have cooler-than-normal weather in the Northeast starting later in March and continuing through April. We expect blocking to develop in the atmosphere," continued Boston. "Basically, that means we'll see cooler air steered down into the eastern U.S. more frequently. I think that may be setting up in late March and into April, making the arrival of spring a little bit sluggish."
Boston also said that much of the rest of the contiguous U.S. will remain warmer with the possible exception of the Pacific Northwest.
"It may stay pretty active up there and get lots of rain and therefore keep their temperatures held down pretty well," said Boston.
Written by John Marsh, Writer for AccuWeather.com
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