Forecasting Flooding In Winter

Late this weekend we have the first potential (and I’ll stress potential) for flooding of the New Year. Forecasting flooding is a difficult task, but during the winter there are a few more variables that are involved that make it more difficult. Here’s a look at what information we look at to forecast flooding.



1)    Rainfall forecast. Typically we don’t get heavy rain in the winter. This is because colder air can’t hold as much moisture as warm air. The moisture content of the air is expected to be 300-400% of what is normal around here. We also look at where that moisture originates. This go around it is the Gulf of Mexico, which can indeed help make things juicy.

2)    Frozen ground. As you may have noticed a frozen ground does not soak up rain very well. Most rain that falls on a frozen ground runs right off and makes its way to streams and rivers fairly quickly.

3)    Snow on the ground. Snow can help prohibit flooding or it can enhance it. Snow can act as a sponge to absorb rainfall, thus limiting run off into area tributaries. However, if temperatures are warm enough and dewpoints rise significantly above freezing then snow can melt rapidly (the closer to a dewpoint of 40 degrees the better).  Snow can also have high water content. Some areas now have 1-3 inches of water equivalent stored in the snow. Click here to check out the current snow cover and water equivalent. When you combine the melting snow and the heavy rain this can lead to more of a rise on area rivers.

4)    River Ice. Ice on rivers can cause ice jams and result in flooding. It is important for us to get reports from folks near the rivers to give us an idea of how much ice might be in their location. If you would like to submit a photo of the river near you email us at stormtrackerweather@wbngtv.com



Some of these variables are easier than others to forecast. Sophisticated Hydrology computer models take these variables (except river ice) into account and produce forecasts at specific forecast points along area rivers. You can always keep track of the rivers here. These models are good, but there is some estimating involved especially with the snow on the ground and how quickly the snow will melt. The potential for flooding is there Sunday into Monday, but it is not a slam dunk. Keep checking back for updates through the weekend.