December 05, 2008
Temperatures May Not Be So Frosty this Winter
LINCOLN, Neb. — The latest three-month forecasts show a good majority of the state should see above-normal temperatures this winter, the University of Nebraska-Lincoln state climatologist says.
Forecasts indicate the eastern two-thirds of Nebraska is projected to have above-normal temperatures, said Al Dutcher, state climatologist in the university's Institute of Agriculture and Natural Resources.
"The highest of this probability is assigned to the southeastern one-third of the state that includes Omaha, Lincoln, Grand Island, Hastings and all areas east and south of there," he said.
When it comes to precipitation, the three-month forecasts show the southern one-fourth of Nebraska looking at a slight likelihood of above-normal precipitation in an area bounded by Imperial, southeastward to Falls City, Dutcher said. Lincoln, Omaha and Grand Island are considered to have equal chances of being above normal, but Hastings would fall in the above normal area.
However, Dutcher said, the latest 30 day forecast, which is issued twice a month, indicates below-normal temperatures for an area east of a line from Yankton, S.D., to Omaha and also indicates an area of above-normal temperatures that includes areas south and west of a line from Ft. Robinson through Holdrege, he said.
"Everybody else is in between with equal chances," he said.
For precipitation, the entire state is indicated to have a slight probability of being above normal with the highest probability assigned to the northwest quarter of the Panhandle.
"The 90-day forecast is not adjusted with the new 30-day forecast issued at the end of November," he said. "However, if you look at the 30-day forecast that was issued at mid-month, it indicated the entire state with above-normal temperatures. So, the shift in the two-week forecast was to a cooler bias outside of areas indicated with above normal temperatures.
"This leads me to believe that the 90-day forecast is very optimistic in terms of temperatures."
Since models are forecasting a cool first half of December, the state will have to see some significantly warmer than normal temperatures in January and February to counter balance this month. December also could be average in temperatures, but models are aggressively pointing to an arctic blast with snow mid-month, he said.
"However, we easily can see above normal snowfall and still have below normal precipitation," Dutcher said. "It really boils down to the quality of the snow, meaning liquid equivalency of that snow."
For example, arctic air usually produces snow with a low moisture content in the ratio of 15-30 inches of snow to 1 inch of water. However, a system coming up from the Texas Panhandle generates a moderate to high liquid equivalence in the 8-10 inches of snow to 1 inch of water range.
Although it will depend on snow accumulation and temperatures, a white Christmas could be in store with numerous chances for snow this month.
"When we talk about the snow probability for Christmas, we are only talking about a one in four chance in the southeastern corner of the state and a one in two chance across extreme northeast Nebraska and along the South Dakota-Nebraska border as it progressively increases across the state from south to north."
Precipitation also is important this year with attention given to next year's growing season.
"We had record to near record rainfall during October across central and south central Nebraska," Dutcher said. "Many locations in the eastern half of the state ranged from 5 to 11 inches. With the wet conditions we had this summer, we have built up substantial soil moisture reserves across the eastern half of the state."
This means the eastern two-thirds of the state does not have a lot of room to put additional moisture.
"Depending on how winter plays out into spring, this becomes a primary importance from a flooding aspect," he said. "There simply isn't a lot of room to store a lot of moisture."
This also may mean muddy conditions this spring at planting time.
However, rainfall has left the Republican River Valley in exceptionally good shape, Dutcher said, compared to previous fall periods going into winter.
"I'm not saying there aren't some problems, but all reservoirs have recovered significantly," he said.
Meantime, the Platte River System, although not full, has seen significant recovery.
As of Nov. 26, the Platte River System, including the reservoirs of Seminole, Pathfinder and Glendo in Wyoming and Lake McConaughy in Nebraska, stood at 40 percent of the entire holding capacity, which represents 1.8 million acre feet of water. That is compared to 1.1 million acre feet at this same period last year.
Seminole is at 51 percent capacity compared to 19 percent at this time last year, Pathfinder is at 38 percent compared to 18 percent last year, Glendo is a small reservoir so it fills up every year, and McConaughy is at 41 percent of capacity compared to 32 percent at this time last year.
Lake McConaughy is 9 feet higher in elevation at this time than it was at this time last year.
"If we get normal precipitation in the mountains leading into the Platte River Basin, I would expect that we should see McConaughy at 60 to 65 percent of capacity," Dutcher said. "I can't say what the snow will do, but even with two banner years the system still won't completely fill up. It will still take an additional winter of above normal snowfall to completely fill the system."
If there is below normal snowfall, last year's gains could diminish from irrigation demands.
"However, it only takes three or four major snowstorms to account for 70 to 80 percent of the total snow pack in the central Rockies," he said. "Right now snowfall is below normal, but the vast majority of snowstorms occur in March and April. So, it is hard to predict right now whether that will occur."
12/5/08-SK Al Dutcher
School of Natural Resource Sciences State Climatologist (402) 472-5206
 
Sandi Alswager Karstens IANR News Service (402) 472-3030
Department:
School of Natural Resources
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