The Science of Extreme Weather

Survey the remarkable range of extreme weather around the planet. Then consider: Why does Earth have weather at all? Professor Snodgrass introduces basic features of the atmosphere that naturally lead to severe weather. He concludes by outlining the goals of the course - among them, preparedness.#Science & Mathematics

Discover the origin of Earth’s great variability in air temperature, and learn how it also explains the seasons. Search for the highest and lowest temperatures on the planet, and the locations with the greatest difference between highs and lows. Along the way, encounter the deadliest weather on Earth.

Witness a demonstration of the power of air pressure and the ability of changing pressure to produce clouds. Learn how fluctuations in air pressure play a role in all weather, propelling everything from the ferocious winds of a tornado to the incredible speeds of the jet stream.

Severe weather is driven by water’s ability to change phase-with energy being released during the transition from vapor to liquid, and from liquid to ice. Calculate the stupendous amount of energy brewing in a typical thunderstorm, and study cases of extreme humidity, rain, and fog.

In this and the next lecture, study the advanced technology that has revolutionized extreme weather forecasting. Here, look at how radar has vastly improved the prediction of tornadic thunderstorms. You’ve seen Doppler radar images in forecasts. Now learn how this all-important tracking tool works.

Venture into space to see how different types of weather satellites chart large-scale extreme weather systems in both daylight and darkness. Compare two nearly identical hurricanes-one in 1900, the other in 2008-to highlight the life-saving capability of orbiting weather stations.

Moment for moment, the one billion volts discharged in a typical lightning strike may be the most extreme of all weather phenomena. Watch lightning unfold in super-slow motion, and gain an appreciation for the exquisite complexity of this electrifying event.

Investigate positive polarity lighting-a bolt up to ten times more powerful than normal lightning-which accounts for five percent of cloud-to-ground strikes. Then hear life-saving tips on how to recognize when you are about to be hit by lightning and what you should instantly do.

Begin a series of lectures on thunderstorms, which are the key to understanding many types of extreme weather. Learn how thunderstorms are forecast, and explore their formation by following a weather balloon on its data-gathering mission through the atmosphere.

Wind shear is the ingredient that turns an ordinary thunderstorm into a monster. Study the mechanisms that underlie this transformation. Then evaluate the crucial difference between a severe weather watch versus a warning, and put yourself in the shoes of a forecaster calling the shots.

Heralded by an ominous-looking formation called a shelf cloud, a squall line is a group of thunderstorms that produces intense, destructive winds. Analyze the anatomy of a squall line, so that you know what to expect next time a shelf cloud approaches. Also investigate microbursts, another dangerous product of thunderstorms.

Pound for pound, the supercell is the most powerful thunderstorm on Earth. Explore the mechanics of this system, which produces the strongest straight-line winds, the most violent tornadoes, and the largest hail. Close by looking at the formation of a record-breaking hailstone weighing almost two pounds!

Tornadoes hit all 50 states of the U.S. and most inhabited regions of the world. Blowing as fast as 200 to 300 mph, they are the most awe-inspiring of extreme weather. But what exactly are they? And why are they more prevalent in some areas than others? Probe tornado facts and myths, and survey some of the deadliest tornadoes of our times.

The genesis of tornadoes takes place under complex conditions that are still being deciphered by meteorologists who make detailed measurements from up close. Go inside a supercell thunderstorm to see a tornado being spawned. Then learn tornado safety tips and the precautions that professional storm chasers take.

Study the impact of mountains on weather by investigating the Chinook winds, which can race down the east face of the Rocky Mountains with tornadic force. Also look at the Santa Ana winds of southern California, notorious for fanning the region’s wildfires. Then explore another aspect of extreme mountain weather: avalanches.

Begin the first of three lectures on winter weather by pinning down the cause of ice storms, which are beautiful but also dangerous and destructive. Professor Snodgrass demonstrates how supercooled water is the source of the freezing rain behind these perilous storms.

The region downwind from the Great Lakes is famous for its lake effect snowstorms, which can total more than 200 inches of snow per year for some locations. Examine the factors behind this phenomenon as well as the mortal danger posed by blizzards, as shown by the tragic Children’s Blizzard of 1888.

Look back at historical blizzards that paralyzed major U.S. cities. Then probe the official definition of a blizzard, the cold-weather cyclone systems that create them, and the revolution in forecasting blizzards since 1993. Focus on the role of the jet stream, and dispel a common misunderstanding of the polar vortex.

Consider the deadly power of moving water. Explore scenarios for extreme flooding in flood-prone regions of the U.S. and consider past cases of extreme coastal floods, river floods, and flash floods. Study the meteorology behind these events, and hear flood safety tips.

From the American dust bowl of the 1930s to the relentless expansion of the Sahara in Africa, drought represents severe weather that can stretch out for years. Explore what’s going on in the atmosphere to create extreme drought, which is associated with heat waves and dust storms.

Begin the first of three lectures on tropical cyclones, known as hurricanes, typhoons, or cyclones depending on where they occur. Plot the historical tracks of these gigantic storms, sharpen your understanding of how they are named, and focus on tropical cyclones that were so notorious that their names have been retired.

How do hurricanes get so big? Start off the coast of West Africa to see how this region is the perfect breeding ground for low-pressure disturbances. Chart the role of the Coriolis force, water temperature, and other factors that must coincide for these systems to grow into hurricanes threatening the U.S.

Hurricanes destroy life and property in four ways: through storm surge, inland flooding, high winds, and embedded tornadoes. Consider examples of each. Then focus on high water as the deadliest factor, responsible for 80% of all hurricane fatalities.

Close by investigating one of the most eventful weather triggers of all: the El Niño-Southern Oscillation, which starts as a warming trend in the eastern Pacific and can lead to extreme weather throughout the world. Our detailed understanding of this once-mysterious phenomenon, as well as other extreme weather cycles, shows how far the science of meteorology has come.