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Category Archives: History
Why is the reference, or normal, climate period a 30-year average?
Climate normals are 30-year averages for various climate observations such as temperature, precipitation and snowfall. A 30-year period smooths out weather variability while getting a good representation of our current climate. The current 30-year normal covers the period 1991-2020. This averaging provides a baseline for comparisons and assessing whether a particular day or month is warmer or cooler than normal, or if it is wetter or drier than normal.
The World Meteorological Organization (WMO) recommends 30 years as the reference for current average conditions, and member nations follow that recommendation. For the United States, NOAA’s National Center for Environmental Information (NCEI) is the official source of the country’s climate normals. The computation is nontrivial and more complicated than one might initially anticipate. Climate scientists employ complex statistical calculations to ensure the observations accurately represent the full 30-year climate period. The determination of normal must account for the occasional missing data, change in station location and instrument upgrades. Continue reading
Has 2026 been an active tornado year?
A tornado is a violently rotating column of air that is in contact with both the surface of Earth and the storm above. The 30-year normal (1981-2010) for Wisconsin is 23 tornadoes per year.
As of mid-July, the National Weather Service has confirmed that our state has experienced 39 documented tornadoes, which ties it with 2025 for the 6th most tornadoes in an entire year. These tornadoes were distributed over 10 different days. Twenty-seven of those tornadoes were spawned between April 13 and April 17, with 16 on April 17 alone. Continue reading
How important was the weather forecast on D-Day?
D-Day was the name given to the June 6, 1944, invasion of the beaches at Normandy in northern France by troops of the Allied Forces during World War II. The goal was to cross the narrow, often stormy, English Channel into Nazi-occupied France.
The successful D-Day invasion required a combination of environmental factors: initial invasion around sunrise and at at low tide; nearly clear skies; at least 3 miles of visibility; close to a full moon; relatively light winds; non-stormy seas; and good conditions persisting for at least 36 hours and preferably for four days. To make the task of forecasting even more difficult, the Allies needed at least two days advance notice of these conditions —and because the science of meteorology was only just beginning to modernize, at the time this was a nearly hopeless task. Continue reading
Category: History, Severe Weather, Weather Dangers
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How is air quality measured and what are the trends in Wisconsin?
The amount and density of pollutants in the air are converted into an Air Quality Index, or AQI. The Wisconsin Department of Natural Resources’ statewide monitoring network is operated following a federally approved plan. The DNR statewide network includes 30 ozone and 18 fine particle, or PM2.5, monitoring sites. PM2.5 describes particles with diameters that are generally 2.5 micrometers or smaller and thus inhalable.
Under the Clean Air Act, the Environment Protection Agency sets National Ambient Air Quality Standards for pollutants. Continue reading
What did the Endangerment Finding suggest about global warming?
On Feb. 12 President Donald Trump’s Environmental Protection Agency revoked the so-called “endangerment finding,” issued in 2009, asserting that “CO2 and other greenhouse gases endanger public health and welfare.” This scientific finding served as the basis for limits on tailpipe emissions and power plant rules enacted under President Barack Obama and committed the United States to a national effort to arrest the kind of pollution that contributes directly to global warming.
Based on an extensive body of scientific evidence, in the EPA in 2009 singled out six greenhouse gases for the danger they pose to public health and welfare. Continue reading
Category: Climate, History, Weather Dangers
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