The Weather Guys

Though a slush puddle may look like a static, unchanging, boring and ugly mixture of dirty ice and water, it is actually an extremely dynamic cauldron of various phases of the magical water substance, constantly undergoing all manner of phase changes. Photo credit: Steve Apps, State Journal archives.

The recent snow and ice followed by a bit of melting filled sidewalks and some city streets with puddles of slush — that wondrous winter concoction of liquid water and ice.

Though it is not possible to see, surrounding any puddle of slush is also a cloud of countless invisible water vapor molecules. In fact, of all the many chemical constituents of the Earth’s atmosphere, only the water substance can naturally occur in all three of its phases – solid, liquid and gas – at Earth temperatures.

And, to add an even greater level of grandeur to this fact, the ice and the liquid water in the slush puddle are constantly subject to sublimation (transitioning from ice to vapor) and evaporation, respectively, while the invisible vapor is constantly liable to deposition (transitioning from vapor to ice with no intermediate liquid stage) and condensation.

So even though the slush puddle looks as if it is a static, unchanging, boring and ugly mixture of dirty ice and water, it is actually an extremely dynamic cauldron of various phases of the magical water substance, constantly undergoing all manner of phases.

These phase changes involve substantial amounts of energy transfer as well. In fact, for a gram of liquid water to evaporate to vapor, 600 calories of energy are required from the environment. When a gram of water vapor condenses, that same amount of energy is given back to the environment.

A scientist’s view of the world need be no less lyrical than a poet’s — we hope you will never see slush puddles the same again.

Cooper Armstrong of Madison works on his chipping game on Dec. 9 before a round at Odana Hills golf course, which reopened so golfers could take advantage of this month’s warm temperatures. Photo credit: John Hart, State Journal archives.

The mildness of the first half of December in southern Wisconsin has probably not escaped anyone’s attention.

Despite the first visit of relatively cold air we just experienced over the weekend, both Madison and Milwaukee have already recorded the second warmest first halves of December in their respective records. Through Dec. 16, Madison’s average temperature for the month was 39.7 degrees, a full 14.4 degrees above the average.

How rare is such a warm first half of December? Of the 10 record-warmest such periods in Madison history, five have occurred since 1998 (the record-warmest year). That is a rather alarming observational fact that strongly supports the myriad other observations that document the reality of global warming.

And since we are likely to record above normal temperatures for a majority of the remaining 10 days of this December, it is likely we will end up with one of the warmest Madison Decembers of all time. This follows a warm November where average temperatures in southern Wisconsin were 5-6 degrees above normal.

This warmth will ensure that the freeze of Lake Mendota will be delayed well into January, perhaps long enough that we will make a run at the latest freeze ever, which is Jan. 30. Stay tuned for more updates on what may be taking shape as a strange, record-setting winter.

The winter solstice (In Latin, sol, “Sun,” and stice, “come to a stop”) is the day of the year with the fewest hours of daylight. In 2015, this occurs for the Northern Hemisphere on Dec. 21 at 10:48 p.m. CST.

As Earth orbits the sun, its axis of rotation is tilted at an angle of 23.5 degrees from its orbital plane. Because Earth’s axis of spin always points in the same direction — toward the North Star — the orientation of Earth’s axis to the Sun is always changing as Earth orbits around the Sun.

As this orientation changes throughout the year, so does the distribution of sunlight on Earth’s surface at any given latitude. This links the amount of solar energy reaching a location to the time of year and causes some months of the year to always be warmer than others — in other words, the seasons.

On the Northern Hemisphere’s winter solstice, the northern spin axis is pointed away from the Sun and latitudes north of the Arctic Circle (66.5°N) have 24 hours of darkness.

The winter solstice is often referred to as the first day of winter. But there are other definitions of winter.

For example, the beginning of winter might be defined on the calendar day, on average, when precipitation has an equal chance of falling as rain or snow. For Madison, that calendar day is Nov. 15.

Meteorologists often define the three months of winter as December, January and February — the coldest months of the year.

Kayla Powell of Lacrosse makes her way past a collection of ice heaves on Lake Mendota in February. With this month’s warm temperatures, it could be a while before the lake freezes again. Photo credit: John Hart, State Journal archives

The climatological ice-on date for Mendota is Dec. 19 but the actual ice-on date in any given winter is highly variable. Given our warm autumn this year, it is likely we will experience a later than normal ice-on date.

Right now the lake’s water temperature is about 7C (45 degrees Fahrenheit) and, importantly, that temperature is nearly uniform throughout the water column. Such uniformity in temperature started about Oct. 1 this year, according to data from the Integrated Nowcast/Forecast Operation System (INFOS) for the Yahara Lakes (www.infosyahara.org/temp_mendota). At that time, the water temperature was about 15C (59 Fahrenheit). Thus, in the past two months, the lake water has cooled by 8C (14 degrees Fahrenheit).

Such cooling requires an enormous amount of energy to be extracted from the lake. Knowing the size of the lake (39.85 million square meters), its average depth (12.7 meters) and the density of water (1000 kg per cubic meter), we know that 507 billion kg of water reside in Lake Mendota. Given the 14-degree temperature change and the fact that 4200 joules of energy must be extracted from each kilogram of water to lower its temperature 1C, we know that 1.7 quadrillion joules of energy have been extracted from the lake since Oct. 1.

Since there are 3.6 million joules in every kilowatt hour (kwH) and the Madison metro area uses about 79 million kwH of energy on a typical January day, we can calculate that the amount of energy thus far extracted from Lake Mendota to get it to its current temperature is enough to power the entire Madison metro area for nearly 60 winter days.

Additionally, it is not until the water temperature cools another 3C (requiring extraction of the equivalent of another 23 days of energy) that the lake is even ready for the additional surface cooling that eventually leads to freezing. It is easy to overlook the fact that truly enormous amounts of energy are being transferred from water to atmosphere before our eyes.