Big snowpack, rapid jump in temps brings 'well above normal flood risk' in coming weeks
Season's final flood outlook from the National Weather Services urges a careful eye on the forecast as snowpack melts.
MONTEVIDEO — With a large snowpack still covering the landscape and forecasts for a sudden jump in temperatures to the 70's, the National Weather Service is warning that the outlook for spring flooding in the coming two weeks is “well above normal.”
The above normal flooding risk includes the Minnesota, Mississippi and St. Croix Rivers and their watersheds.
The current snowpack is “unprecedented for this time in April,” according to the flood risk outlook issued on Thursday. The snow water equivalent in the Willmar area is 5.9 inches. It’s 4.8 inches at Madison.
The forecast cautions that it has been difficult to accurately measure the water equivalent in this year’s snowpack.
Higher flows that could reach flood levels are expected in the coming week in the smaller streams and channels in the watersheds, with the higher flows to show in the rivers the following week.
The risk of flooding due to ice jams is elevated in the tributaries as well, the flood outlook noted.
The outlook pointed out that a significant snowmelt has already occurred in southern Minnesota in the lower Minnesota River watershed. That helps reduce the flood risk as the remaining snowpack melts.
The outlook cautions that there are a number of uncertainties in predicting the potential flood levels. It’s difficult to know how quickly the rapid switch to warmer temperatures will melt the snowpack. The snowpack ranks in the top one to three in the records for this time of year.
There is also uncertainty about how much of the snow melt will be absorbed by the ground. The region is no longer in a drought. Much of the melt that has already occurred has gone into the ground since the frost has left. How much capacity remains in the soil for the remaining snowmelt is not know.
The biggest uncertainty is how much precipitation may occur in the coming two weeks. Fortunately, the current forecast for the coming week does not include significant rainfall. The longer range forecast includes a potential uptick in precipitation in the following week.
Stay tuned to forecasts, as there is uncertainty ahead.
“The kind of temperatures on this kind of snowpack is very rare, and thus the uncertainty of how the rivers will react is increased,” stated National Weather Service Meteorologist Craig Schmidt in the report.
At this point, the flood forecast for Montevideo includes a 50% probability of reaching major flood level, and a greater than 60% risk for moderate flood levels.