LINCOLN, Neb. -- While snow blankets much of the country, mountain snow pack across the central and northern Rockies has been poor, which based on present conditions will likely cause the Platte River system to fall short of last fall's stream flow expectations, the state climatologist says.
The latest stream flow projections from the Natural Resources Conservation Service based on snow surveys conducted at the beginning of February present a disappointing picture for this summer, said Al Dutcher, state climatologist in the Institute of Agriculture and Natural Resources at the University of Nebraska-Lincoln.
Only the very southern extent of the Rocky Mountains that feed the lower Colorado River basin currently are expected to see above-normal snow melt, he said.
Snow melt within the northern branch of the Platte River currently is projected at less than 75 percent of normal.
"Any chance to recover from current snow pack deficits depends on the strength and longevity of the current El Nino pattern," Dutcher said. "With the two most crucial snow-making months of the season yet to come, both in terms of amount and water content, there is hope that some of the current snow deficits can be eliminated."
However, until the current El Nino pattern dissipates, storm activity is expected to pass south and north of the region, he said.
Current model forecasts indicate El Nino likely will continue into April or later, reducing the likelihood that major snow storm activity will return to the central Rockies.
Current stream flow rates continue to exceed last year's on the northern and southern branches of the Platte, meaning subsoil moisture has been a contributing factor for improved flows.
The moisture received during October improved surface moisture across the central Rockies, and along with increased river flows, should help mitigate some of the expected runoff declines this spring.
"The most disappointing aspects of this poor snow pack winter is the fact that the Platte River systems stood an excellent chance to undo the damage of the past decade with normal inflows," Dutcher said. "It was entirely possible that all Wyoming reservoirs on the Platte would have filled under normal snow pack, with McConaughy possibly reaching 80 percent of capacity.
"Unless snows returns with a vengeance over the next 10 weeks, it will be at least another year before Wyoming reservoirs completely fill."
The real dichotomy in snow activity can be seen in relation to the extent of water contained in the current snow pack across the lower 48 states, Dutcher said.
"There is an extensive area of deep snow pack and high water content (in excess of 3 inches) over Iowa, southern Minnesota, southwest Wisconsin, eastern Nebraska, and the eastern Dakotas," he said. "These same areas received 200 to 400 percent of normal moisture last October, leading to saturated surface conditions."
As for flood risk, there is little, if any, wiggle room.
"The first issue is how to get ice moved downstream with minimal impact from ice jams," Dutcher said. "Second, will a short intense warm spell, possibly accompanied by rain, materialize that could release much of the water over a couple day time span? After the snow disappears, how extensive will spring planting delays become with just normal rainfall?"
The last time such a large portion of the western and central Corn Belt faced such a significant flood risk going into the early spring was 1993.
Heavy snowfall during the late winter and early spring across the upper Mississippi River valley led to extensive flooding during the spring planting and the summer growing season.
"At this point in time, water in the snow pack that is currently above the soil surface exceeds 1993 in aerial coverage," Dutcher said. "Unless a dry pattern similar to last spring across the western Corn Belt materializes, flooding is likely across a large percentage of the western and central corn belt."
Above-normal moisture and below-normal temperatures have been the trend during four of the last five months across this high risk area, he said.
Only November saw above-normal temperatures and below-normal moisture.
"This is certainly a trend that the central Rockies could use to improve the current snow pack, but one that would likely result in a major nightmare across much of the Corn Belt," Dutcher said.
Source: Al Dutcher, associate geoscientist, School of Natural Resources, (402) 472-5206, adutcher1@unl.edu
Writer: Sandi Alswager Karstens, IANR News Service, (402) 472-3030, salswager2@unl.edu
