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Published December 02 2010

Forum editorial: Too early to predict a big flood

When snow comes early, as it has this year, residents of the Red River Valley begin to worry about the effect of November snowfall on spring flooding.

Fall snow doesn’t always mean a major spring flood on the Red and its tributaries. But the record shows that eight of the 15 wettest falls on record (September to November precipitation) were followed by major flooding the following spring. But the record also shows that moisture in the fall is not always a predictor of flooding in the spring. For example, in some of those years, fall moisture was more than 9 inches, but there was no spring flood. On the other hand, in a couple of years fall precipitation was below 8 inches, and there were major spring floods.

One conclusion that can be gleaned from the historical record is that fall moisture is but one factor in a major spring flood. In many instances, fall weather has not been a major factor. As an expert with the National Weather Service said, fall precipitation is only a fraction of the flood picture.

The other weightier factors are total winter snowfall, the melt pattern, soil moisture and spring rains. Another factor that has been difficult to gauge is the regional wet cycle that has been in place since about 1993. The Red’s vast watershed has soaked up more rainfall than long-term averages during that time – a situation that keeps river levels and water tables high. Soils stay saturated so snowmelt and rainfall that might percolate into the ground instead run off into streams and rivers.

It’s early in the flood outlook season. The first official outlook will come in February toward the end of the region’s long winter. But as of today the valley’s relatively snowy November is no clear indication that a major flood is likely – or unlikely.

Forum editorials represent the opinion of Forum management and the newspaper’s Editorial Board.