What is the status of the ozone hole?

Posted on May 27, 2025 by WeatherGuys Editor

This year is the 40th anniversary of the discovery of ozone hole. On 16 May 1985, British Antarctic Survey scientists published research that revealed a significant drop in ozone levels above Antarctica, referred to as the “ozone hole.” Stratospheric ozone loss has also been observed over the Arctic.

Variations of ozone from year to year. The red bars indicate the largest area and the lowest minimum value. The year-to-year fluctuations are superimposed on a trend extending over the last three decades. (Image credit: NASA GSFC’s Ozone Watch)

Ozone (O3) is a molecule formed by three oxygen atoms. In the lower troposphere O3 is considered a pollutant, as it can cause respiratory problems when breathed. Ozone in the stratosphere absorbs UV rays from the sun, protecting life on Earth from harmful radiation that can cause skin cancer and other health problems.

Scientists found that chlorofluorocarbons (CFCs), used in aerosol cans and refrigerators at the time, were destroying the stratospheric ozone. This discovery led to the 1987 Montreal Protocol, an international agreement to freeze production and consumption of ozone-depleting substances at 1992 levels.

Thanks to the cooperation of scientists, governments, and industry, the use of CFCs declined drastically. Later amendments tightened restrictions with global CFC production and consumption phased out by 2010.

Satellites are used to routinely monitor the ozone levels in the atmosphere. Antarctic ozone depletion is seasonal, occurring primarily in late winter and early spring (August-November). Peak depletion occurs in early October. The size of the Antarctic ozone hole is gradually decreasing. In 2024, the ozone hole was the seventh smallest since monitoring began in 1992. CFCs can remain in the atmosphere for 50 years or longer, so full recovery may not happen until after 2070.

The global response to the ozone hole crisis demonstrates the effectiveness of integrating science, diplomacy, and policy. The Montreal Protocol is regarded as one of the most successful international environmental agreements in history. It highlights the advantages of addressing issues proactively and underscores the significance of expert knowledge in resolving such matters.

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

Category: Climate, Phenomena

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Is there a windiest time of year in Madison?

Posted on May 19, 2025 by WeatherGuys Editor

With the pollen season peaking in southern Wisconsin one may wonder if there actually is a windiest time of year in Madison.  Of course, a windy day can come along just about any time of year (the record gust of 83 mph in Madison occurred in June 1975) but the climatology suggests that March and April are the windiest months of the year with average wind speeds of 11.3 and 11.4 mph, respectively. November through February are not far behind logging a four-month average of 10.5 mph.

Graph of monthly average wind speeds in Madison. (Image credit: Wisconsin State Climatology Office)

The fact that it’s windier during the cold season is not surprising as that time of year is characterized by the highest frequency of mid-latitude cyclone activity. Mid-latitude cyclones are large in scale, covering several states simultaneously, and are often associated with very large differences in sea-level pressure over small distances. It is these pressure differences that drive the wind.

The particular maximum in March and April may reflect the fact that late winter and early spring storms have a higher chance of containing thunderstorms that can locally enhance the winds. It may also be that on a sunny March or April day the daytime heating contributes to a slightly breezier day than might be observed on a similarly sunny day in the depth of winter.  With regard the pollen issue, it is interesting that the windiest month (April) occurs when plants are most in need of assistance in spreading pollen and reproducing. The power of evolution!

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

Category: Climate, Seasons, Severe Weather

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Why is May 6 such a special day in weather science history?

Posted on May 12, 2025 by WeatherGuys Editor

Immediately after WW II, it became fashionable to imagine technologies that might allow human beings to control the weather.  In fact, one goal advanced by influential scientists was actually to explode nuclear bombs in the right locations and in the right quantity so as to alter the weather in favorable ways.  Such an enterprise would require accurate forecasts of the weather thought possible by using the brand new computer technology to make the millions of requisite calculations. 

NOAA historic weather computer circa 1965, used to process weather data for short and long-range forecasts, analyses, and research. (Photo credit: NOAA’s National Weather Service Collection)

The drive to use computer models for weather forecasting was initiated at a secret meeting at the U.S. Weather Bureau headquarters in Washington D.C. on the rainy morning of January 6, 1946.  After a series of successes and setbacks that mostly discouraged the broad meteorological community, the first operational computer generated forecasts were issued on the afternoon of May 6, 1955. 

Thus, in less than 10 years the notion of computer-based forecasts went from dream to reality.  In the intervening 70 years the combination of increased theoretical understanding both of meteorology and computational science, increased observational capacity (a good deal of which stems from satellite data), and sheer hard work on the part of a legion of dedicated scientists has resulted in our current forecasting capability. 

The fact that our ubiquitous smart phones give everyone access to quite reasonable forecasts several days in advance is the end result of what might be considered the greatest scientific advance of the second half of the 20th century.  So, as you consult your phone for the forecast, remember that one of the first baby steps in the march toward the modern miracle of numerical weather prediction were taken just over 70 years ago.

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

Category: History

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When will we have our last spring frost?

Posted on May 5, 2025 by WeatherGuys Editor

The latest frost in spring is important to gardeners as we seek to protect our garden plants from freezing temperatures. For Madison, based on temperature observations between 1940 and 2024, the latest frost occurred on 10 June 1972 and the earliest final frost occurred on 7 April 1955. The last frost date varies from year to year as it is strongly dependent on current weather conditions. To best estimate the last frost is to use statistics over a given time period. The median date for the last frost in Madison is May 5.  Giving the median date of last frost means that there is still a 50% chance that a frost will occur after this date. 

This map of the United States shows the most common date range you can expect to see temperatures dip to 32°F or below for the last time. The map also reveals some interesting regional differences across the country. (Image credit; NOAA’s National Centers for Environmental Information)

An analysis of Madison’s last frost date from 1940 – 2024 shows a trend consistent with the scientific expectations of global warming, that the last frost date now occurs earlier in the spring. Our nighttime minimum temperatures have been getting warmer and that too is consistent with the last frost date moving earlier. 

In addition to following local forecasts, there are some observations you can make to aid in predicting the formation of frost in your yard.  If at sunset the temperature is close to freezing, then there is a better chance for the formation of frost overnight.  Clouds are good emitters of infrared energy so they reduce the energy losses at the ground during the night. If it is cloudy and will stay cloudy, then the likelihood of frost is reduced. Knowing the dewpoint is also important. A rule of thumb–if the dew point is above 45°F at sunset then you are probably OK. If below 40°F, you will probably see a frost if the other weather conditions are aligned.

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

Category: Climate, Seasons

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What causes tornados and do they have a lifecycle?

Posted on April 28, 2025 by WeatherGuys Editor

A tornado is a powerful column of winds that rotate around a center of low pressure. The winds inside a tornado spiral inward and upward, often exceeding speeds of 300 mph. We don’t know if a particular storm will produce a tornado but we do know the necessary conditions needed for tornado formation.

The required conditions for a thunderstorm to produce a tornado are warm humid air near the surface with cold dry air above. These conditions make the atmosphere very unstable, in the sense that once air near the ground is forced upward, it moves upward quickly and forms a storm. Severe thunderstorm conditions also include a layer of hot dry air between the warm humid air near the ground and the cool dry air aloft. This hot layer acts as a lid that allows the sun to further heat the warm humid air, making the atmosphere even more unstable.

An idealized cross section of a mature supercell with some major features and wind flow patterns. Except for the rotating updraft (the definition of a supercell) not all of these features are necessarily present or visible in every storm. (Image credit: NOAA’s NWS Stormspotter Guide)

To form a tornado, the host thunderstorm also must rotate. This happens in a storm when wind at the ground is moving in a different direction and speed than the air above. The change in wind speed and direction with height is known as wind shear. This wind shear develops the rotation in the thunderstorm needed for tornado formation.

Once formed, tornadoes exhibit a typical four-stage life cycle. The first stage is the organizing stage, during which a funnel cloud picks up debris as it reaches the surface and widens. The mature stage follows when the tornado is often at its peak intensity and width. The tornado reaches the shrinking stage when its funnel narrows, and it ends with a decaying or “rope” stage. At this point, the funnel thins out to a very narrow, ropelike column, after which it eventually dissipates.

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

Category: Meteorology, Phenomena, Severe Weather

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