MOLINE, Ill. — It's no secret this past winter has been an easy one. While we did have a couple of instances of heavy snow and bitter cold, overall, the winter was quite warm and tame.
We managed to break quite a few records and also logged the third warmest winter on record in the Quad Cities! Linda from Moline, Illinois brought up an excellent question regarding frost in the ground. She asks, "With such a warm winter, how deep did the frost go?" Let's dig in!
How do we measure frost?
This process is quite easy! You can even make your own frost tube to measure the frost depth right in your backyard using these instructions.
Meteorologists and observers use a small, hollow tube that is inserted into a drilled hole in the ground. Another inner tube filled with water is placed inside, and the depth is determined by the line where the water freezes. In the picture above, the yellow-colored water denotes frozen, while the green is unfrozen.
A freakishly mild winter
This past winter was highly unusual in many ways. Yes, it was the third warmest winter on record, but it was also a winter season that logged the warmest temperature ever when we reached 79 degrees for a high on Feb. 27. That was also the warmest February temperature ever recorded in the Quad Cities.
Total snowfall ended up being slightly more than average, with just a little more than 30 inches falling throughout the season. There was one storm in particular, though, that came through in January, dropping our largest single accumulation for the season. More about the perfect timing of this snowfall in just a moment.
One of the things that I like to reference when determining how severe or non-severe our winter has been, is the Accumulated Winter Season Severity Index, which is put together by the Midwestern Regional Climate Center.
This index is made using several variables, including the amount of snow, temperatures and how long the snow sits on the ground. Our winter season officially runs from Dec. 1 to Feb. 29. During that period, the majority of our winter season was rated mild. The exception was those couple of winter storms that moved through in January along with some short-lived bitter cold. Once we got deeper into February, a much warmer pattern took over and moved our overall winter season severity to mild, the least severe level on the scale.
How much, or little, frost was there?
Remember those two large winter storms in January that dumped our single highest accumulation for the winter season? Well, that snow fell right before the biggest cold snap of the season. The impact? The deep snowpack helped insulate the ground during that entire bitterly cold period, which only lasted a few days. For the winter season, frost was only observed in the ground at Davenport for a period of two days and at a depth of 5". That's it!
We have reliable frost depth data from NOAA dating back to 2011. With some help from Masha Hoy, a hydrologist with NOAA at the North Central River Forecast Center, I was able to see just how uncommon a shallow and short-lived frost depth like that was. The graphic above depicts not only the depth of the frost but also the duration. Notice how incredibly short this winter season was! This isn't the most dramatic one, though, as according to this data there was essentially no frost during the winter of 2018!
You can definitely see a trend, and that trend is down when it comes to the amount of frost in the ground during the winter seasons. Very interesting! It also matches up well with the fact that winter is the fastest warming season in the Quad Cities.
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