What's Going On With The Warm December Weather
Here is a preliminary look at the warm December 2011 weather observed across much of south central Nebraska and north central Kansas. For many more details, stay tuned to the top of our web page in the coming days for the "December 2011 Weather and Climate Review"...
Temperature:. The average daily temperature for December 2011 finished 1-3 degrees above normal across most of South Central Nebraska and North Central Kansas (please note: the average daily temperature is an average of both the daily highs and lows).
Precipitation: The average precipition for the month of December is 0.63 inches. Thanks to two separate snowfall events early in the month, 1.11 inches of liquid equivalent precipitation accumulated at Grand Island in December 2011.
Snowfall:The December 2011 snowfall for Grand Island, NE was 8.3 inches, which represented the 25th snowiest December on record for the site. The snowiest December was December 2009, when 26.5 inches of snowfall accumulated over the course of the month. No snowfall has accumulated during the month of December 15 times, last achieved in 2006.
So why has it been so warm lately? And how long will it continue?
Mid to late December 2011 was unusually warm across the Central Plains. Since the 10th of the month, 19 of the last 21 days recorded warmer than average temperatures at the automated weather stations in both Grand Island and Hastings Nebraska.
Why has it been so warm lately?
1. There is virtually no snowpack across the Plains and Midwest, except for a ribbon of snow from southwest to central Kansas. When there is snow covering the ground, it reflects some of the sun’s energy, and more of the sun’s energy is used to work on melting the snow. Without the snow covering the ground, the sun’s energy can go into heating the ground and the air. Also, when the winds blow in from the north and northwest, they aren’t blowing over a snowpack and cooling down.
2. The North Atlantic Oscillation, or NAO, (and its sister, the Arctic Oscillation, or AO) have been positive since late November. The NAO is known to have an effect on the climate cycle. When the NAO is negative (like it was in 2009-10 and 2010-11), the area east of the Rockies tends to be colder than normal. When the NAO is positive, as it has been so far this winter, the area east of the Rockies tends to be warmer than normal. Unlike ENSO, which stays in one direction throughout the course of a winter, the NAO can bounce between positive and negative phases. But when it’s pretty strong in one direction, it tends to linger there. So far, that has been the case this winter. The NAO is powerful enough that its temperature signals can override the ENSO effect. (We saw this in 2009-10, when a very strongly negative NAO combined with a moderate El Niño. El Niño is often associated with warmer than usual temperatures in the northern Plains into the northern Great Lakes, but the negative NAO overruled it, creating colder and snowier than normal weather instead.) Unlike ENSO, however, the NAO is not very well predicted beyond a period of about 10-14 days.
3. Randomness. The random nature of weather patterns alone has a large influence on the weather that we ultimately get.
How long will the warm weather continue?
Temperatures are forecast to remain above normal through the early January. In fact, beyond a cold front expected New Years Day, temperatures are expected to return to the mid 50s for the later half of next week. In addition, the most recent 8 to 14-day outlook from the Climate Prediction Center indicates about a 60% chance for temperatures to be in the warmest third of climatology (1981-2010), with about a 40% chance for the weather to be in the driest third of climatology, through the 11th of January.
For the latest forecast information, head to the NWS Hastings NE page: