Jim Bennett

couple weeks of very cold weather left us with a short memory. Remember the mild winter we had going until a week into February. One Arctic Plunge and we remembered what a real winter was like. It was like a punch in the stomach when it hit 20 below with a cold that penetrates clothing and we ask ourselves why we chose to live here.

Remember the warm early winter? That lack of real cold from November to the end of January had most ice anglers leaving their cars and trucks parked on the road or in a group on a shallow bay. That’s something I just don’t understand. When I see ten trucks parked together at the boat launch I start to drive out on the lakes I know.

But how does ice form and how fast is it freezing in this weather?  Everyone without a snowmobile or 4 wheeler were walking out, pulling sleds with all their ice fishing gear in tow.  The question then was how long will it take the ice to get thick enough to drive out and feel safe doing it? According to “my fishing partner.com” there are highly scientific mathematical formulas based on degree days over the past 24 hours that seem to provide the answers.

You start by taking an average temperature over the past 24 hours. Let’s say the daytime high was 30 and the low at night was 20. That means the average temperature was 25.  You simply subtract the average temperature from 32, (32-25=7). That gives you 7 freezing degree days (FDD’s). If the high was 20 and the low zero the average temperature would be ten. 32 minus 10 equal 22 FDD’s. To figure out how fast ice forms you need to start out with a lake that has at least some sheet ice on it. Then you need a score of 15 FDD’s to form an inch of ice.

On February 11 we had a high of minus 2 and a low of 20 below. Your average will be negative 11. When you subtract negative 11 from 32 you get positive 43. Forty three divided by 7 equals 6.1428. That’s how many inches of ice, 6.14”, will form using the formula presented. But of course there are always considerations that compound the formula. 

One of these factors is snow. Snow acts as an insulation blanket and that slows the freezing process down. How much slower does it get? It’s 50% slower with a foot of snow.  As winter reaches the end of the road the thickness of the ice will also slow ice formation on lakes because it’s another insulation blanket. That is why ice at the Arctic and Antarctic does not freeze all the way to the bottom! All of this info should make it easier to figure out when we have safe ice to drive out on next year!


Jim Bennett is an outdoorsman who lives and worked in the St. Croix River Valley and can be reached at jamesbennett24@gmail.com

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