As residents across the eastern United States continue to dig out from an endless stream of snow storms, mountain snow pack across the central and northern Rockies has been nothing short of disappointing. Whether snow pack levels can recover from deficits likely will depend on the strength and longevity of the current El Nino event.

The latest stream flow projections from the National Resource and Conservation Service, based on snow surveys in early February, present a disappointing picture for this summer. Only the very southern extent of the Rocky Mountains that feeds the lower Colorado River basin is expected to see above normal snowmelt. Snowmelt in the northern branch of the Platte River is projected to be less than 75% of normal.

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. Until the current El Nino pattern dissipates, which isn’t expected until April or later, storm activity is expected to pass south and north of the region.

Current stream flow rates continue to exceed last year on the northern and southern branches of the Platte, indicating that sub-soil moisture has been a contributing factor. October moisture did improve 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 aspect of this poor snow pack is that the Platte River systems stood an excellent chance to undo the damage of the past decade. With a normal winter snow pack it was entirely possible that all Wyoming reservoirs on the Platte would have filled, with McConaughy possibly reaching 80% 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 lies in the difference between the lack of snow pack in the Rockies and the extent of water in snow pack across the lower 48 states. 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.

These same areas received 200% to 400% of normal moisture last October, leading to saturated surface conditions. There is little, if any, wiggle room in regard to flood risk, which leads to several questions:

• How can the potential impact from ice jams be minimized as ice moves downstream?
• What happens if a short intense warm spell, possibly accompanied by rain, releases much of the water over a couple days?
• After the snow disappears, how extensive will spring planting delays become with just normal rainfall?

Comparison to 1993

The last time that such a large portion of the western and central Corn Belt faced such a significant early spring flood risk was 1993. Heavy snowfall during the late winter and early spring across the upper Mississippi River valley, led to extensive flooding during spring planting and the summer growing season.

Current indicates are that water in snow pack above the soil surface exceeds 1993 levels. Unless a dry pattern similar to last spring’s materializes across the western Corn Belt, flooding is likely across a large percentage of the western and central Corn Belt.

The trend has been for above normal moisture and below normal temperatures for four of the last five months across this high risk area. Only November saw above normal temperatures and below normal moisture.

Continuation of this trend could be positive for snow pack in the central Rockies, but a nightmare for much of the Corn Belt.

Al Dutcher
Extension State Climatologist