Predicting floods in January


image courtesy NOAA

It’s impossible to predict a March or April flood in January with certainty, and National Weather Service experts don’t try to do that. What they do is run lots of data through computer models at the North Central River Forecast Center in Chanhassen, Minn., and offer statistical probabilities. It’s a little like the severe thunderstorm watch. It means conditions are right for severe weather/flooding.

Just like a severe summer weather watch, the idea is to get the attention of local residents and city officials. And it works. In Fargo Moorhead the flood outlook is likely more noticed than winning Powerball numbers.

To get those numbers, forecasters gather mountains of data and run it through complex computer models.

They look at soil moisture. This fall, soils across much of the Red River Valley were like a dripping sponge. They monitor stream flows. This winter many streams are at record or near record levels because lakes and reservoirs are full. A large area of western Minnesota and eastern North Dakota ended the fall about 12 inches above normal rainfall for the year. That means when the spring melt starts those streams will already be high.

Hydrologists also measure snow depth and how much water is in the snow. This year has been snowy across the entire country. Fargo Moorhead is nearly on pace with the record setting winter of 1996-97. The dark purple on the image above represents the deepest snow. There’s already a normal winters worth of snow on the landscape.

That tells hydrologists all of what they call precursors are in place for a busy spring flood season.

The wild card is what happens between now and April. Long range forecasts say it will be wet and cold. Wet is bad for obvious reasons. Cold is also bad because it could stretch out winter and delay the spring melt. The longer cold weather stretches into April the more likely it is to warm up quickly and bring April showers.

Of course, the forecast could be all wrong. But don’t bet on it.

Thoughts of filling a couple million sandbags should be enough to warm the coldest Fargo Moorhead resident on a -20 January night.