Did weather forecasting play a role in D-Day?

Posted on June 9, 2025 by WeatherGuys Editor

Last Friday was the 81st anniversary of the Allied invasion of Europe that began with the landings on the beaches at Normandy.  The combined land, air, and sea assault of June 6, 1944 remains the largest such event in history.  The success of the invasion was extraordinarily dependent of weather conditions.  More than three months before the invasion, a combined British and American forecasting team began rigorous forecast exercises designed to iron out the physical and logistical kinks of such a coordinated effort.  As June drew near, the nature of this collaboration was still problematic as the two groups employed vastly different methods in fashioning the requisite 3-5 days forecasts – at the time, absolutely primitive in the underlying science as compared to what is possible at such ranges today.  The British were attempting to make such forecasts based upon the understanding of atmospheric dynamics that had grown substantially during the war.  The Americans were employing a method based on a statistically- based search through old weather data for historical analogues that could be used to guide the forecast.

To maintain secrecy, a large portion of the Allied fleet was squirreled far away in northern Scotland.  Consequently, 5 days of lead time was required to mobilize these forces.  Thus, General Eisenhower needed to know by May 31 whether the first week of June, the prospective target for the invasion, would provide favorable weather.  The forecasters foresaw a break in that year’s unusually stormy late spring and suggested June 5 would work.  As the day approached, the team realized that a one-day postponement would offer better conditions prompting Eisenhower to make the fateful decision to invade on June 6, under barely acceptable conditions.  Had the Allies delayed, the combination of lunar cycle, tides and weather almost certainly would have postponed the invasion for more than a month likely costing the effort the tremendous advantage of secrecy. 

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, Meteorology, Severe Weather

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Is there scientific consensus on global warming?

Posted on June 2, 2025 by WeatherGuys Editor
Yearly surface temperature from 1880–2024 compared to the 20th-century average (1901-2000). Blue bars indicate cooler-than-average years; red bars show warmer-than-average years. NOAA Climate.gov graph, based on data from the National Centers for Environmental Information. (Image credit: https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature )

Global warming refers to the recent rise in Earth’s average temperature caused by human activities that emit higher levels of greenhouse gases like carbon dioxide and methane. Scientists understand the physics and chemistry of how these gases warm the atmosphere.

The global average temperature has increased about 1.7°F since 1970. During this same period, temperatures have risen around 2.5°F in the contiguous United States and 4.2°F in Alaska. The 10-year period 2014–2023 was the warmest decade on record.  Such warming has, of course, altered average weather conditions, including temperature, precipitation, humidity, wind patterns, atmospheric pressure, and ocean temperatures and so global warming is nearly synonymous with climate change. Although it is difficult to directly attribute specific weather events to global warming/climate change, data analysis indicates that global warming is linked to more extreme weather events such as droughts and floods. There has also been an increase in days with temperatures above 90°F and heat waves.  Heat waves, defined as periods of unusually hot weather lasting two or more days, have become more frequent in major cities across the United States, rising from an average of two heat waves per year in the 1960s to over six per year in the 2020s.

The Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (their synthesis report was published in March 2023), represents the work of hundreds of leading experts in climate science. That report states, “It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred.” 

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, History

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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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