What is the shape of raindrops?

Posted on April 13, 2026 by WeatherGuys Editor

While cartoonists typically draw raindrops like a teardrop or a pear shape, raindrops are not shaped like that.

Shapes of raindrops (Image credit: https://www.usgs.gov/water-science-school/science/are-raindrops-shaped-teardrops )

They are drawn as teardrops to give the image of falling through the atmosphere, which they do. But as they fall, raindrops are flattened and shaped like a hamburger bun by the drag forces of the air they are falling through.

Raindrops are at least 0.5 millimeters or 0.02 inches in diameter. You will not find a raindrop bigger than about one-quarter of an inch in diameter. Larger than that, the drop will break apart into smaller drops because of the air resistance. Precipitation drops smaller than 0.02 inches in diameter are collectively called drizzle, which is often associated with stratus clouds.

The typical speed of a falling raindrop depends on the size of the drop. Gravity pulls everything downward. As an object falls it experiences a frictional drag that counters the downward force of gravity. When the gravity and frictional drag are balanced, we have an equilibrium fall speed that is known as the terminal velocity of the object. The terminal velocity depends on the size, shape and mass of the raindrop and the density of the air. Thus, it is worth talking a bit about the shape and size of raindrops.

A large raindrop, about one-quarter of an inch across or about the size of a house fly, has terminal fall speeds of about 10 meters per second or about 20 mph. That kind of speed can cause compaction and erosion of the soil by the force of impact. Since raindrops come in a variety of sizes, they fall with different speeds. The smallest raindrops fall at about 2 mph. Water droplets smaller than these smallest raindrops (known as cloud liquid water droplets) can resist falling in the atmosphere because there is upward moving air that overcomes the force of gravity and keeps them suspended in the cloud.

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

Comments Off on What is the shape of raindrops?

How is air quality measured and what are the trends in Wisconsin?

Posted on April 6, 2026 by WeatherGuys Editor

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.

Average Annual Population-Weighted concentration (PM2.5) trend in Madison (Image credit: State of Global Air.org)

Under the Clean Air Act, the Environment Protection Agency sets National Ambient Air Quality Standards for pollutants.

The DNR monitoring network is operated under a federally approved network plan, reviewed annually to ensure appropriate monitoring in all locations as required by federal regulations.

Continuous monitoring enables the determination of trends in air quality, which demonstrates how well air pollution controls and programs are working to improve our air quality. The monitoring also enables the DNR to rapidly inform the public when air pollution reaches unhealthy levels.

The data indicate that the concentrations of most pollutants regulated under the Clean Air Act have been decreasing across the state since the early 2000s, an indication that air quality is improving. However, in the most recent years, their report shows that ozone and PM2.5 concentrations have leveled off or recorded increases in concentrations.

The Endangerment Finding, established by the EPA in 2009, authorizes regulation of emissions from various sources, including vehicles and power plants. Without the Endangerment Finding, the U.S. would have fewer tools to curb emissions linked to greenhouse gases and poor air quality.

Recently, under the Trump administration, the EPA rescinded the Endangerment Finding, which could reduce regulatory oversight and worsen air quality. It will be important to continue collecting data on air quality to determine future impacts of this regulatory change.

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

Comments Off on How is air quality measured and what are the trends in Wisconsin?

What are ice balls and how do they form?

Posted on March 30, 2026 by WeatherGuys Editor

If you were lucky enough to be walking along Lake Mendota shoreline at Shorewood Hills and Frautschi Point on March 16, 2026, you might have seen ice balls, or ice eggs, floating in the water.  This was a rare occurrence of naturally formed balls of ice that form in cold water.

Linda Deith photographed this flotilla of grapefruit-size ice eggs bumping up against the Lake Mendota shoreline on March 16. (Photo credit: Linda Deith)

While they look a little like hail, the formation of ice balls is very different. The freezing temperatures form sheets of ice on the water surface. The wind and the resulting wave action causes the ice sheets to break up and form small pieces of ice and slush. The gentle tossing of the water by a breeze causes the pieces of ice to collide and stick together. Single balls of ice begin to form in the ebb and flow of water and grow as layers of water freeze over the surface of the ice balls. Eventually the wind and water currents move the ice balls to the shoreline where they collect.

The weather conditions must be just right for ice balls to form along a shoreline that is shallow with gentle slope. The temperatures must be slightly below freezing (32°F). The water must be calm with a light swell, and the wind must blow in a steady direction.

Ice balls have been observed in the Great Lakes and along several Arctic shorelines, including those of Estonia, Russia, and Northern Germany. Their sizes have been observed to range from golf ball size to 3 feet in diameter.  In 2016, ice balls washed up on a beach in Siberia with some measuring about 3 feet in diameter and covering an 11-mile stretch of coast.

The ice eggs along Lake Mendota were estimated to be the size of a grapefruit.

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: Uncategorized

Comments Off on What are ice balls and how do they form?

What is clear air turbulence?

Posted on March 23, 2026 by WeatherGuys Editor

Clear-air turbulence, or CAT, is the turbulent movement of air masses in the absence of any visual clues such as clouds. The atmospheric region most susceptible to CAT is at altitudes of around 23,000 to 39,000 feet. This is the region of jet streams — fast-moving, narrow bands of wind high in the atmosphere that blow from west to east.

National Center for Atmospheric Research (NCAR) is national center that made scientific advances in understanding and predicting Clear Air Turbulence. Their headquarters are in Boulder CO. (Photo credit: UCAR Center for Science Education)

Wind shear refers to a sudden change in wind speed or direction across a short distance. When an aircraft encounters wind shear, it may experience abrupt vertical or horizontal movements, resulting in unanticipated changes in altitude or velocity. While wind shear is commonly observed in the vertical dimension, it can also manifest horizontally.

A primary theory explaining CAT posits that vertical wind shear generates atmospheric gravity waves, which subsequently break in a manner similar to ocean waves approaching shore. The disturbance produced during the breaking of these gravity waves is analogous to the foam created by ocean waves, the “foam” representing atmospheric turbulence.

CAT is a destroyer and even a killer on occasion. On Dec. 28, 1997, United Airlines Flight 826, carrying 393 people, hit heavy turbulence over the Pacific Ocean. Passengers who happened to be wearing their seat belts at the time described floating “like we were in an elevator falling down.” Those not wearing seat belts crashed into the cabin ceiling. One woman was killed as the result of severe head trauma and at least 102 people were injured.

CAT is a particularly difficult challenge for weather forecasters. The chances of encountering CAT increase when: a) the vertical wind speed shifts by at least 5 knots every 1,000 feet; b) the horizontal wind speed changes by 40 knots or more across 150 miles; or c) two air masses moving at significantly different speeds come together.

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: Phenomena, Severe Weather

Comments Off on What is clear air turbulence?

How might climate change impact insects?

Posted on March 16, 2026 by WeatherGuys Editor

Global warming can result in a multifaceted set of pressures on insect populations. Insects are cold-blooded and rely on ambient temperatures to regulate their internal body temperature. Unlike mammals, insects are more at the mercy of a hot environment because they can’t cool themselves by sweating or panting. That makes them vulnerable to extreme weather and temperature fluctuations. Their main defense strategies for excessive heat involve finding shade or burrowing underground.

Most insects are susceptible to heat stress between 82 and 90 degrees Fahrenheit. The observed warming trends contribute to an increased frequency of heat waves, which threatens some insect species. The increased heat waves can push some insect species beyond their thermal tolerance. Some recent research indicates that 25 out of 38 insect species studied may face increased extinction risk over the next century, driven by temperature changes in their habitats.

Regarding cold tolerance, most insects do not function below 50°F. Warmer winters can boost survival rates and help expand habitats that are suitable for certain disease-carrying insects like mosquitoes. Warmer average temperatures may lead to better reproduction and increased survival of these vectors, which raises concerns about their spread to areas that previously did not have them. This expansion creates notable risks for the transmission of diseases such as malaria, dengue fever, and West Nile virus.

A warmer climate system will intensify Earth’s water cycle. Heavy rainfall and flooding also threaten some insects as it can dislodge them from plants, change soil properties, and force those who live underground to come to the surface, increasing the risk of predation.

Scientific reports have highlighted a decline in insect populations in both temperate and tropical ecosystems. This trend is worrying because insects serve as a crucial food source for many larger animals, such as birds, bats, reptiles, amphibians, and fish. Additionally, some insects play vital roles like pollinating crops and wildflowers.

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

Comments Off on How might climate change impact insects?