Has this year’s tornado activity been abnormal?

Posted on May 20, 2024 by WeatherGuys Editor

A remarkable number of tornadoes have occurred across the United States this year.

Preliminary reports from the Storm Prediction Center tally 784 tornadoes across the United States through May 13, the second-largest number on record. That number is far higher than the historical average to that date of 549.

Storm Prediction Center running total for 2024 tornadoes, as of May 19th.

Remarkably, however, this year’s total pales in comparison with the 1,314 tornadoes that had visited our country by the same date in 2011. That year’s total of 2,240 exceeds the next highest total (1,677 in 2019) by 33.6%. Other seasons that crossed the 700 tornadoes threshold by mid-May were 2023, 2022 and 2017. Of those three, 2017 ended with the largest total (1,522, third all time).

It is hard to say whether this rapid start to the season will mean that 2024 will contend for a top spot on this harrowing list. It is also very difficult to say whether the background climate change has played a role in increasing the number of tornadoes the country experiences.

Recent work by Victor Gensini at Northern Illinois University and Harold Brooks at the National Severe Storms Laboratory has found that Tornado Alley has shifted eastward during the past 40 years. Once again, the role of background climate change in this shift is an open question.

Regardless of the cause, such trends are important for understanding the potential for changes in tornado exposure. These storms, and the associated severe thunderstorms that deliver them, are responsible for an average of $5.4 billion in damages each year across the United States — with seasons exceeding $10 billion in damages becoming more common.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Meteorology, Severe Weather

Comments Off on Has this year’s tornado activity been abnormal?

Do tornadoes occur over all parts of Earth?

Posted on May 14, 2024 by WeatherGuys Editor

The only continent that has not recorded a tornado is Antarctica. Otherwise, tornadoes can happen in just about any location.

A tornado spins west of Hawley, Texas.
(Credit: R. Erdrich, Abilene Reporter-News)

North America, and specifically the United States, accounts for more than 75% of the world’s reported tornadoes. Other tornado-prone areas around the globe include western Canada, Argentina, the western Mediterranean, Japan, Bangladesh, Australia, New Zealand and South Africa.

Tornadoes form in regions of the atmosphere in which warm moist air is surmounted by warm dry air, large vertical wind shears exist, and weather systems such as fronts or thunderstorm complexes can force air upward. The U.S. provides these three ingredients in abundance. The distribution of tornado reports reveals a “tornado alley” of highest frequency in the central Great Plains. In this region, warm moist low-level air from the Gulf of Mexico is often capped by very dry air blown out over the Plains at mid-levels from the Mexican Plateau. This type of stratification sets the stage for the explosive thunderstorms that can spawn tornadoes. Another area of frequent tornado occurrence is over the Southeast.

Although tornadoes can occur at any time of day or night, favorable tornadic conditions benefit from solar heating. Therefore, the most likely times for tornadoes are late afternoon or early evening. In fact, more than half of all U.S. tornadoes occur between 3 and 7 p.m.

The total number of tornadoes in the U.S. each year has stayed relatively consistent over the past several decades. Recent research has indicated that there are now fewer days with tornadoes each year, but there are more tornadoes on the days when they do occur, indicating that they tend to now happen in more concentrated bursts over fewer days of the year.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Phenomena, Severe Weather

Comments Off on Do tornadoes occur over all parts of Earth?

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

Posted on May 6, 2024 by WeatherGuys Editor

Immediately after World War 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.

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 Jan. 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 69 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 69 years ago today!

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: History, Meteorology

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

How does hail get its shape?

Posted on April 29, 2024 by WeatherGuys Editor

Hail is precipitation in the form of balls or chunks of ice.

Hailstones begin as small ice particles that grow primarily by accretion; to grow large, they require abundant water droplets. As the hailstone moves up and down through a storm, it collides with water droplets and ice crystals, growing larger with each collision. Hailstones can be smaller than peas or as large as oranges and grapefruits. The small hailstones are roughly spherical in shape, while large ones can take on jagged shapes.

When a hailstone is cut in half, you can see rings of ice. Some rings are milky white; others are clear. This ringed structure indicates that hailstones grow by two different processes: wet growth, represented by the clear layers, and dry growth, which forms the milky white layers. Counting the layers of clear and milky white ice gives an indication of how many times the hailstone traveled through the storm.

This hail stone from Madison Wisconsin exhibits both dry and wet growth. (Credit: M. Mooney)

Dry growth of hailstones occurs when the air temperature is well below freezing. In these conditions a water droplet freezes immediately as it collides with the hailstone. This quick freezing leads to air bubbles “frozen” in place, leaving cloudy ice.

In wet growth, the hailstone is in a region of the storm where the air temperature is below freezing but not very cold. When the hailstone collides with a drop of water, the water does not freeze on the ice immediately. Instead, the liquid water spreads over the hailstones and slowly freezes. Because the water freezes slowly, air bubbles can escape, resulting in a layer of clear ice.

With wet hail growth, a thin layer of liquid water can remain on the surface of a hailstone. This thin layer helps hailstones that collide to freeze to each other, forming jagged shapes.

Steve Ackerman and Jonathan Martin, professors in the UWM Adison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. send them your questions at stevea@ssec. wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Severe Weather

Comments Off on How does hail get its shape?

Are ‘chem trails’ a real thing?

Posted on April 23, 2024 by WeatherGuys Editor

For years we have fielded questions on our monthly radio show on WHA regarding the nature of condensation trails left in the wake of jet airliners.

Widespread contrails over the southeast U.S. in January 2004. Credit: NASA MODIS

These contrails are composed of ice crystals that develop from the exhaust of jet engines in portions of the atmosphere that contain sufficient water vapor. Sometimes these condensation trails can persist for a very long time because the environmental conditions are moist enough that sublimation (the direct transformation from solid ice to invisible water vapor) is easily resisted by the aircraft-produced ice particles.

Sometimes there is not enough water vapor available along a portion of a flight route for the formation of a trail. The variability of upper tropospheric water vapor is such that sometimes the same aircraft can create a condensation trail along a segment of its track and nothing along an immediately adjacent segment.

With the increase in air travel over the past half century, these interesting, thoroughly explainable and naturally occurring results of air travel have become the font of an enduring conspiracy theory which suggests the condensation trails are actually “chem trails” — short for “chemical trails.” The idea is that some governmental agency is responsible for producing these “chem trails” for any of a number of malevolent purposes, including altering precipitation patterns so as to create drought, altering the chemical composition of the atmosphere so as to promote global cooling, etc.

None of these theories is in any way valid — and all of them disregard the enormous scale of the clandestine enterprise that would need to be taking place in order for such schemes to have any discernible impact on the atmosphere. It has taken over a century of continuing, unchecked increase in carbon dioxide from the burning of fossil fuels to have produced the actual climate change that many of the same people warning about “chem trails” deny has even begun. And yet, just last week, the state of Tennessee succumbed to this nonsense and passed a bill that forbids “intentional injection, release, or dispersion” of chemicals into the air — code for eliminating “chem trails.”

We live in a strange time.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Phenomena

Comments Off on Are ‘chem trails’ a real thing?