What are cooling degree days?

Posted on October 8, 2012 by Weather Guys Editor

A degree day is a measure of heating or cooling. A degree day is defined as a departure of the mean daily temperature from a given standard: one degree day for each degree of departure above (or below) the base temperature during one day. The degree day is related to the outside temperature and is not related to time.

A cooling degree day is every degree that the mean temperature is above 65 degrees during a day. So, if the high temperature for the day is 95, and the minimum is 51, the average temperature for the day is 73. That would be 8 cooling degree days (73-65).

The amount of energy required to maintain a building’s temperature in the summer is proportional to the accumulated cooling degree days. Cooling degree days, or CDD for short, are used to estimate fuel consumption needs.

The typical accumulated CDD for Madison is 664. The recent hot summer has, so far, registered 1065 CDDs — well above normal.

Of course, cooling a building depends on total energy gains and losses of the building and not just the mean temperature outside. Other factors, such as cloudiness, insulation and the number and efficiency of electrical appliances running will influence energy needs.

We also compute growing degree days, GDD, which is used by farmers to predict plant growth such as when a flower will bloom or when a crop should reach maturity. During winter, we keep track of heating degree days, or HHD. Each degree that the mean temperature is below 65 degrees is one heating degree day.

The Wisconsin State Climate office publishes this data at go.madison.com/madisonclimate.

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How is the ozone hole doing?

Posted on October 1, 2012 by Weather Guys Editor

Currently, the ozone hole is not as large as it was in 2011, but it is larger than it was in 2010. The ozone hole refers to the rapid depletion of stratospheric ozone over Antarctica. This ozone is located in a layer about 15 miles above the surface.

Human activity has contributed to the deterioration of the ozone layer by adding chlorofluorocarbons, or CFCs, to the atmosphere. These chemicals were invented by chemists to be used as propellants in spray cans, as Styrofoam puffing agents and as coolants. These chemicals are very stable and once injected into the atmosphere can remain for decades and are transported all over the globe, including over Antarctica. Once they are high over Antarctica, CFCs can significantly deplete the stratospheric ozone layer.

During Antarctica’s winter, a vortex of winds develops around the pole and isolates the polar stratosphere. Very cold temperatures can then develop (109 degrees below zero Fahrenheit), which helps to form thin clouds made of ice, nitric acid and sulphuric acid mixtures. Stratospheric temperatures in the mid-latitudes, where we live, do not get this cold. As the sun rises in the Southern Hemisphere in springtime (e.g., late September), a crucial ingredient is added — UV radiation. The combination of UV radiation, stratospheric clouds and chemicals results in a rapid destruction of ozone.

This September we celebrate the 25th anniversary of the Montreal Protocol, an international treaty to end the production of ozone-destroying chemicals. The Montreal Protocol is working, as ozone depletion due to human effects is starting to decrease. Unfortunately, even with the Montreal Protocol, the ozone hole is expected to stay around until about 2050.

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Did we hit record for 90-degree days?

Posted on September 25, 2012 by Weather Guys Editor

Though it isn’t unprecedented to get another day above 90 degrees this late in the year (the all-time latest such day in Madison’s history is Oct. 14, 1975), it is very likely our run at the record of 90-degree days in a season will end at 39 — agonizingly one day shy of the record 40 set in 1955.

Looking back, it was the lack of really warm days in August (only seven days over 90) and thus far in September (only two) that foiled our pursuit of the record. September 1955 had five such days with the 40th day at or above 90 that season occurring on Sept. 18.

The weather was very interesting in the week preceding that record-setting warm day. On Sept. 9, 1955, the high temperature was 97 and yet the low temperature just two nights later was a chilly 34. The very next night (Sept. 12) the low temperature dropped to 31 but did not go below freezing again until the night of Oct. 18.

So far this season (as of Sept. 20), we have not had an overnight low temperature below freezing. It appears this summer, incredibly warm as it was, will come up just short of a rather formidable record.

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What is the Beaufort scale?

Posted on September 17, 2012 by Weather Guys Editor

The Beaufort scale is a method of estimating wind speed based on the general condition of the surface of a large body of water with respect to wind waves and swell. This scale allows sailors to estimate the wind speed just by observing the state of the sea surface.

The scale has a long history, but was finalized in 1805 by Rear Admiral Sir Francis Beaufort, an Irish hydrographer in the British Royal Navy. It was officially first used during the voyage of Charles Darwin on HMS Beagle. The Beaufort scale can also be applied to conditions on land, but it is most often associated with the sea state.

The modern day Beaufort scale consists of 13 numbers ranging from 0 to 12. A Beaufort force 0 is assigned to calm winds where the water surface is smooth. A Beaufort force 12 occurs with waves greater in height than 46 feet and the sea is completely white with foam and spray with greatly reduced visibility. Such conditions are associated with wind speeds of greater than 74 mph, which are hurricane-force winds.

The National Weather Service defines sustained wind speeds of 39-54 mph as a gale, and forecasters typically issue gale warnings when winds of this strength are forecast. A Beaufort force 6 is a near gale with wind speeds between 25-30 mph and includes white foam from breaking waves that begins to be blown in streaks along the wind direction. A Beaufort force in the range of 6 to 7 is designated as strong winds; 8 to 9 as gale force winds; and 10 to 11 as storm force winds.

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What’s so funny about climate change?

Posted on September 12, 2012 by Weather Guys Editor

In his acceptance speech at the Republican National Convention, Republican presidential candidate Mitt Romney jokingly upbraided his opponent for campaigning on climate change and the impact it’s having on the planet.

“President Obama promised to begin to slow the rise of the oceans and heal the planet,” Romney said to a mix of laughter and boos from the assembled crowd. “My promise is to help you and your family.”

This column avoids politics, but we are equipped to speak about science.

Sea level rise is a real problem. The oceans are rising as the planet warms up, in part because the volume of water is expanding due to the extra heat, and in part due to the ongoing melting of polar ice.

The composition of our atmosphere has changed as a result of human activity on the planet — changed to the point where the climate itself has responded with its own changes.

These changes may well affect our ability to produce adequate food for a growing global population while putting our national commercial infrastructure at greater risk to extremes in the day-to-day weather, to name just two possible ramifications.

Climate change is a serious issue, and policymakers would do well to plan for the challenges it poses to our way of life.

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