The Weather Guys

Heavy storms July 10 caused flooding around the Madison area, including partially submerging this soccer goal along Mineral Point Road near West Towne Mall. In total 6.52 inches of rain has fallen in Madison this month, 2.72 inches above normal. (Photo credit: Barry Adams, State Journal archives)

It seems likely that most of us would consider this month of July to be an exceptionally wet one and, in many ways, that is true.

First of all, we have received measurable rain on 11 days this month and a trace of rain on six other days. Thus, well over half of the days this month have involved precipitation.

In total, 6.52 inches of rain has fallen on Madison this month. With no more precipitation today, that would put us 2.72 inches above normal for July. So, it has been a rainy month – but not everywhere in Wisconsin.

For instance, Milwaukee has totaled only 3.69 inches this month, barely (0.35 inches) above its monthly average. Rhinelander has received only 1.62 inches of rain in July, which is a little more than 2 inches below its normal for the month.

As rainy as it has been in Madison, it has been even worse in La Crosse (7.63 inches, which is 3.78 inches above normal for July) and Chicago (7.68 inches, 4.40 inches above normal).

Of course, anyone who has been outside this month will also recognize it has been a mosquito-heavy month. This is directly related to the rainfall as nearly two dozen species of mosquitoes hatch during the summer, in serial fashion, so a prolonged wet summer tends to result in lots of bugs.

It could all be worse, though. In July 1950, Madison received 10.93 inches of rain, which is the record for the month.

That soggy July is not even the wettest month of the year in Madison, as the all-time wettest month here was August 2007 when 15.18 inches of rain fell.

If a sidewalk is salted, ice may absorb the salt, which lowers its freezing point and may lead to melting. (Photo credit: Baraboo News Republic archives)

All objects exchange energy with their environment. They do this via conduction, advection, convection and radiation. If water is involved, a change in the water phase (liquid, solid or gas) also will involve an exchange of energy.

Conduction moves energy by physical contact. Convection results from hot air rising. Advection by the wind moves heat horizontally.

Radiative processes transfer heat throughout the entire atmosphere and into space. Radiation can be absorbed, reflected or transmitted. Convection and latent heating transfer heat over great distances through vertical motions and phase changes of water.

In the case of ice on a sidewalk, assuming the sidewalk has not been salted and there is no wind, the important energy exchange mechanisms are conduction and radiation. The ice is exchanging energy with both the sidewalk and the air around it via conduction.

If the atmosphere is below freezing, this will not result in the ice melting. If it is night time, and the sidewalk is below freezing, then this will not result in the ice melting. But during the day, the story could be different.

If the sun is shining on the ice, some of that solar energy will be absorbed. Ice is clear at visible wavelengths, the energy to which our eyes are sensitive. But the sun emits radiation at other wavelengths which water will absorb, and thus increases its energy gain.

If these gains exceed the energy losses, the ice will warm. If it reaches the melting point, the ice will start to melt. The sun can also add energy and warm the sidewalk, increasing its temperature to above freezing. This will then warm the ice via conduction and lead to its melting.

If the sidewalk has been salted, the ice may absorb the salt, which lowers its freezing point and may lead to melting.