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Monthly Archives: February 2025
What is this upside-down icicle?
The accompanying photo was taken by Daniel Dettmers in the morning of February 4 on frozen Lake Kegonsa. The high on the previous day was 37°F. This caused puddles of water to sit on the ice of Madison’s regional lakes during the day. Tuesday morning’s low temperature was below 20°F with calm winds. These are just the right conditions to form what are called ‘ice spikes,’ as shown in the photograph.
When water freezes, it expands and becomes less dense. Ice floats on water. But if the lake ice is thick, when puddles form on a warm day, they sit on the ice surface. With the cold nighttime temperatures, the surface of the puddle freezes, trapping liquid water below. As the puddle freezes, it can leave a small hole in the surface of the ice. Continue reading
Is it getting windier in Wisconsin?
Wind speed and direction are variables that change over space and time, and conditions can change considerably from month to month, as well as from year to year. Scientifically assessing any long-term changes in weather elements requires a long-term data set of accurate measurements. Temperature data goes back hundreds of years, and even thousands of years, using ancillary data such as from tree rings.
Wind is a more difficult parameter to study and analyze. The observations of wind speed and direction need to be made at the same height above the surface. The type of surface also impacts the measurement, as the wind sensor should not be too close to trees or buildings. Finally, large annual fluctuations make long-term trends difficult to detect. Continue reading
