The Weather Guys

Since Dec. 1, Madison and Dane County have received approximately 40 inches of snow — 3 inches above normal for that span.

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 40 inches of snow began as the equivalent amount of water in the invisible vapor, or gas, phase before being transformed into solid water.

Everyone knows that 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 40 inches of snow since Dec. 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 approximately 8.8 years. Clearly, there are huge amounts of energy involved.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

What a strange month January 2023 was in Madison.

The cloudiness was remarkably persistent and, though we don’t have a measurement of that variable for the month at hand, anecdotal assertions we have heard suggest that Madison got only about 8% of its possible January sunshine this past month.

Thanks to a major snow event the last weekend of the month, in which 7.3 inches of snow fell on Saturday and Sunday combined, we ended up at just about a normal amount for the month (13.9 inches was 0.2 inches above the average).

Of all the strange aspects to the last month, however, the strangest might just be the temperature. For almost the first four weeks of the month (that is, through Jan. 27) we averaged 10.53 degrees above normal — way out of line.

In fact, had we managed to remain at that pace we would have ended up with the third-warmest January ever recorded in Madison, behind January 2006 (plus 11 degrees) and 1933 (plus 10.7 degrees).

As it was, the snowstorm on Jan. 28 ushered in a fairly significant cold spell during which we recorded our coldest morning of the season at minus 11 on Jan. 31. We ended up at 7.3 degrees above normal for the month, which was still the eighth-warmest January ever in Madison. Milwaukee, at 7.9 degrees above its normal, recorded its fourth-warmest January ever.

Of course, none of this has much to say about what February might be like, but it is true that, climatologically at least, we have already been through our coldest week of the winter.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

A weather forecast of snow indicates a steady fall of snow. The forecast may be modified by terms such as “light,” “moderate” or “heavy” to indicate the intensity of the snowfall.

The intensity is measured in terms of visibility during the snowfall:

• Light snow — visibility of 1 kilometer (1,100 yards) or greater.
• Moderate snow — visibility between 0.5 kilometer (550 yards) and 1 kilometer (1,100 yards).
• Heavy snow — visibility of less than 0.5 kilometer (550 yards).

A forecast for intermittent snowfall often refers to light snow falling for short durations. No accumulation, or a light dusting, is expected. The National Weather Service defines snow flurries as intermittent light snow. Snow flurries are short durations of snowfall and produce no measurable precipitation, only trace amounts. Snow flurries tend to come from stratiform clouds.

The term “snow shower” refers to a short period of light to moderate snowfall and is characterized by a sudden beginning and ending of the snowfall. Some accumulation is possible. The atmosphere is susceptible to the development of snow showers when the difference between the surface temperature and the temperature some distance above the ground is large.

Snow squalls are brief, intense snow showers accompanied by strong, gusty winds. Accumulation of snow on the ground may be significant during snow squalls.

Blizzard conditions include winds greater than 35 mph with heavy snow or blowing snow. Visibility is poor, less than a quarter of a mile, and these conditions are expected for a period of three hours or more.

Snow is difficult to measure because it can be moved by the wind. Newly fallen snow is reported in inches to the nearest tenth of an inch. The measurement is taken as soon as the snowfall has stopped. Meteorologists use a snowboard — a flat wooden surface -– and measure in a location where drifting does not usually occur.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.