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

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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

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Was the February 23 snowstorm in the Northeast really unusual?

Posted on March 9, 2026 by WeatherGuys Editor

The northeast United States experienced a once-in-a-generation storm on Feb. 23-24. It would take too much space to list all the remarkable snowfall records that were set during this event, though mentioning a couple is both irresistible and instructive.

5-minute GOES-19 Mid-level Water Vapor (6.9 µm) images with 3-hourly analyses of Surface Pressure (beige) and Surface Fronts (cyan), from 1001 UTC on 22 February to 0201 UTC on 24 February [click to play MP4 animation] (Image credit: CIMSS Satellite Blog)

Southeast Massachusetts and most of Rhode Island were hardest hit by both the snow and winds associated with this event. T.F. Green International Airport at Providence, Rhode Island, ended up with 37.9 inches of snow — its all-time two-day and single-day records — and suspended all operations on Feb. 23. Hurricane-force wind gusts were widespread in the region, with Wellfleet, Massachusetts recording a peak gust of 98 mph.

This fury was powered by a rapid intensification of the associated cyclone, which, importantly, stayed well offshore throughout its lifetime. Early in the day on Feb. 22, the storm’s central sea-level pressure was a modest 1009 millibars (mb) off the North Carolina coast. Less than 24 hours later it had dropped to 966 mb — 43 mb lower. This represents approximately 4.3% of the atmospheric column directly above the storm center having been excavated in just one day.

This can only be accomplished through incredible upward vertical motions of the air, which, in addition to lowering the sea-level pressure and, consequently, whipping up the winds, also provide the means by which clouds and precipitation are produced in such storms. With such remarkably vigorous vertical updrafts occurring on a multi-state scale, enormous amounts of precipitation were produced.

The storm was not only a spectacular natural event; it was also a benchmark for the astounding progress that has been made, rather silently, over the past few decades in weather prediction. Several days in advance of its initial appearance, the potential storm was garnering attention from forecasters all along the northeast coast of the U.S. Highway traffic signs announcing “Blizzard conditions expected” were lighting up I-195 in New Jersey as many as 36 to 48 hours before the first snowflake fell. Similarly, schools were canceled well in advance and travelers were alerted by commercial airlines to the threat well before it was occurring.

It was a real triumph for our ever-improving forecast capabilities.

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, Seasons, Severe Weather

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What is a mesonet and what are they used for?

Posted on March 2, 2026 by WeatherGuys Editor

The term “mesonet” is a blending of the words “mesoscale” and “network.”

The weather station delivers near real-time data on precipitation, air and soil temperature, humidity and wind speed. (Photo credit: https://wisconet.wisc.edu/about/instrumentation)

In meteorology, “mesoscale” refers to weather events that range in size from about one mile to about 150 miles. Mesoscale events last from several minutes to several hours. Thunderstorms, snow squalls and wind gusts are examples of mesoscale events. A mesonet refers to a network of collectively owned and operated automated weather stations that are installed close enough to each other and report data frequently enough to observe mesoscale meteorological phenomena.

Typically, each observation station in a mesonet is independent, operated by battery or solar panels. Each station records temperature, humidity, wind speed and direction and atmospheric pressure. Some mesonets also measure solar energy, soil temperature and soil moisture. Observations are transmitted to a base station for distribution and long-term storage.

A mesonet can provide realtime 24/7 weather information on a local to regional basis and observe rapidly changing weather conditions that may be significantly different from the conditions over a larger area.

Mesonet data improves weather prediction and is especially beneficial for short-range mesoscale forecasting and tracking hazardous weather. In addition to meteorologists, mesonet data is used for decision-making by firefighters, transportation departments, farmers and agricultural entities — anyone who needs fine-scale weather information. Mesonets also provide data to a wide variety of researchers, scientists and teachers.

The Wisconsin Environmental Mesonet, or Wisconet, is a valuable state resource. This network monitors weather and soil conditions across Wisconsin (wisconet. wisc.edu). There are 78 sites that provide measurements across various ecosystems that reflect Wisconsin’s unique geography. The web interface makes data access easy. Wisconet data is publicly available and may be used commercially under the Creative Commons Attribution license.

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, Seasons

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What did the Endangerment Finding suggest about global warming?

Posted on February 23, 2026 by WeatherGuys Editor

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.

Rescinding the Endangerment Finding weakens regulating greenhouse gases, potentially leading to increased emissions and reduced protections for public health and the environment. (Image credit: US Environmental Protection Agency)

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.

It is well known that Trump considers global warming a “hoax” — but it is equally well known that his opinion is ridiculous and utterly without merit. In fact, this very winter, the one in which we suffered from a robust cold spell in late January, is now just days away from becoming the warmest Northern Hemisphere winter since at least 1948-49.

This declaration derives from analysis of observations, not idle speculation or guesswork. The areal extent of air as cold as or colder than -5 degrees centigrade at about one mile above the surface is a routinely available observation, and this year’s Dec. 1-Feb. 28 period is poised to be the smallest integrated value of that measure seen in modern times. This particularly “warm” year is the 79th entry in a time series that has steadily decreased over nearly eight decades and robustly testifies to the reality of global warming.

Scientifically, the dangers posed by these gases still exist, and now those emissions are not regulated. “Revoking” a scientific conclusion borne of an impartial analysis of evidence is nothing more than asserting an alternate reality — a behavior that appears to have become so common in the current administration as to have become a malignant standard of practice. Nothing good ever comes from ignoring a problem.

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, Weather Dangers

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