Wednesday, 23 May, 2012

What is sleet? ENLARGE Photo: Generation X-Ray When precipitation droplets refreeze before hitting the ground, you get sleet. Sleet is translucent balls of ice that are frozen raindrops. The most common forms of precipitation are rain, snow, freezing rain, and sleet. In Wisconsin, precipitation usually begins as ice particles in a cloud. The temperature conditions [...]

What is the coldest wind-chill temperature ever recorded in Madison? Photo: LongitudeLatitude The face of a frigid windchill. The wind-chill temperature describes the increased loss of heat by the movement of the air. The wind-chill is relevant to humans and other animals that need to maintain a constant body temperature. The cooling power of the [...]

Where does the water come from in Midwestern snow storms? ENLARGE Photo: NOAA/NASA GOES Project Water can travel a long way to dump onto the Midwest as snow. This picture shows the storm system that cause the massive February 2011 storm. Last week we were visited for the second time this winter by a sizable [...]

Do abundant snowstorms suggest global warming is not occurring? ENLARGE Graphic: Rutgers University Global Snow Lab This graphs shows the area of land covered by snow over the past few decades in North America. No. These storms are individual weather events, which cannot be used to support or refute climate trends. Which also means that [...]

Why do bridges ice before the road? People in cold climates are used to signs warning that “bridge freezes before road.” Water on surface will freeze once the surface becomes cold enough, but why does the road cool faster? ENLARGE Photo: Petelewisr Beware of the bridge on an icy day! Warming and cooling result from [...]

What is freezing rain? ENLARGE Photo: Mike Giovinazzo Freezing rain covers everything with a sheet of ice. When water particles fall from clouds and reach the surface as precipitation, they do so primarily as rain, snow, freezing rain or sleet. The many types of precipitation occur because water can change phase as it falls. In [...]

Why does snow disappear? ENLARGE Photo: Amanda Graham Sublimation in action. When the snow builds up on my patio, it starts to evaporate after a few days, even though the temperature is still below freezing. On average, what percentage of our snowfall each year evaporates back to the air? The transition of water from the [...]

How do ice ridges form on a lake? ENLARGE Photo: Jeff Miller Pressure ridge near shore on Lake Mendota in Madison, WI Lake ice formation is dynamic. Even when a lake is completely frozen, the ice is not stagnant. It expands and contracts as it warms and cools. Differences in day and night temperatures can [...]

Why do I feel colder on a damp day? © S.V. Medaris A damp, January morning brings hoarfrost to a Wisconsin farm. Let’s define a damp day as one with high relative humidity but without precipitation or fog. High relative humidity reduces evaporation, which can be dangerous in high temperatures. Although air temperatures are too [...]

What happens when people throw boiling water in the air on a cold day? You can watch videos on the web, but this is a great experiment to try at home, if you do it carefully and don’t burn yourself! On a day with very cold, dry air, throw a cup of boiling water into [...]