The Weather Guys

UW-Arboretum in winter: Hoar frost at the Duck Pond. (Photo credit: Fred Best, SSEC)

Since the beginning of this year, Madison and Dane County have received about 35 inches of snow.

Snow is a form of solid water and water is the only substance that occurs naturally in all three phases — solid, liquid and invisible gas — in the Earth’s atmosphere. Of course, that means that the 35 inches of snow began as the equivalent amount of water in the invisible vapor (gas) phase before it was transformed into solid water.

Melting ice into liquid water requires energy. Not surprisingly, energy is also required to transform liquid water into water vapor, the familiar process of evaporation. The particular amounts of energy needed to accomplish these changes of phase are known as latent heats — the latent heat of melting for the first one and the latent heat of evaporation for the second.

When a cloud of invisible water vapor condenses into a puddle of liquid water, the latent heat of condensation (equal to the latent heat of evaporation) is released to the environment. Also, when that puddle freezes into ice the latent heat of fusion (equal to the latent heat of melting) is similarly released, incoherently, to the environment.

Since we know the depth of liquid-equivalent precipitation involved in delivering us 35 inches of snow since Jan. 1, the area of Dane County, and the latent heats of condensation and fusion, we can calculate how much energy has been released to the atmosphere in the production of that much snow.

Without providing the details of the calculation, we can report that the amount of energy involved could power the entire Madison metro area for about 7.7 years. Clearly, there are huge amounts of energy involved.

The predictions made by this folk forecast are correct only about 40 percent of the time — vastly inferior to what is delivered by modern science. If you flip a coin, you’ll be right close to 50 percent of the time.

This year’s prediction by the furry animal is for an early spring. As for a more scientific approach, temperatures over the next six weeks look about average.

The forecast made on Groundhog Day is an example of predicting the weather based on folklore. If the groundhog comes out of its hole and sees its shadow, we are in store for 40 more days of winter.

Long before computers, the Weather Channel and the internet, humans needed weather forecasts. Farmers and sailors particularly needed to know if storms were approaching. Over time, various folklore forecasts, often in the form of short rhymes, were devised and passed down through the generations.

Although memorable, the folklore forecasts are of uneven quality — some good, others bad.

The roots of Groundhog Day go back to the 6th century. Feb. 2 is 40 days after Christmas and is known as Candlemas. On this day, candles that are used for the rest of the year are blessed. This is also about the midpoint in winter, in meteorological not astronomical terms. The forecast rhyme goes:

If Candlemas Day is bright and clear
There’ll be two winters in that year;
But if Candlemas Day is mild or brings rain,
Winter is gone and will not come again.

If the day is bright and clear, the groundhog “sees” his shadow and we have more winter. Of course, after Feb. 2, there are only 47 days left of astronomical winter — which ends on or about March 21, so the forecast accuracy should be more than luck.

Of course, the weather conditions on Feb. 2 at single locations like Sun Prairie or Punxsutawney, Pennsylvania, tell us very little about the weather for the rest of the winter season. Right or wrong, they are fun community celebrations.

Jimmy the Groundhog famously bites the ear of then-Sun Prairie Mayor Jon Freund in 2015!