Heavy Snow Cover Increasing Spring Flood Threat Across Northland
March will bring a slow-motion thaw and a mix of snow and rain events. Of course rain accelerates snowmelt, and considering much of the Northland has picked up 90-110" of snow so far this winter, there is justifiable concern about the prospect of spring flooding. The potential for spring flooding is higher, but the extent and intensity of any flooding will depend on a myriad of factors, including:
- How quickly we warm up. Will we see a gradual thaw or a sudden warming trend into the 50s?
- How much rain accompanies inevitable March and April warm fronts. Light gentle rains will mean a gradual meltdown. Sudden, heavy rains would accelerate run-off, increasing the potential for flooding on rivers and streams, with less water soaking into our soil.
Reality check: both the factors above are impossible to predict weeks in advance. But the potential for flooding is higher - so we need to be prepared.
The Duluth office of the National Weather Service says the potential for spring flooding is increasing, as snow cover increases and rain gets absorbed into that snow pack.
Meteorologists refer to "SWE" or Snow Water Equivalent, which is a fancy way of saying how much water is locked up in the snow cover. The western Lake Superior basin has 5-8" of liquid water trapped in the snow, which is well above average.
A picture does, in fact, tell a thousand words in the map above, where the darker the blue, the greater the amount of water trapped in the snow pack, compared to normal.
Dr. Kenny Blumenfeld is Minnesota's Senior Climatologist, with a good perspective on the overall flooding risk and the ingredients necessary for serious flooding. Here is a portion of what he shared in an email. "But we don't know the fate of the water sitting in the snow because we don't know how that snow will melt. Light steady rains and/or slow, metered melts have shown themselves to be somewhat friendly to soil replenishment. Heavy rains and rapid melts are friendlier to runoff. So I can tell you what I hope happens, but not what I think will happen...not yet anyway!" Blumenfeld wrote.
The next update from the Duluth National Weather Service comes March 9. Rapid warming, coupled with heavy rain, would increase runoff and the potential for serious spring flooding. That scenario may play out - it's still much too early to know, but the old Boy Scout Motto is ringing in my brain.
Be Prepared (for anything).