Category Archives: Severe Weather

What is a ‘bomb cyclone’?

The term “bomb cyclone” refers to the formation and rapid development of a mid-latitude cyclone. A mid-latitude cyclone is a large-scale, low-pressure system, characteristic of the middle latitudes, that has counter-clockwise flow around its center (in the Northern Hemisphere).

A primary measure of development in these storms is a drop in the atmospheric pressure at the center of the storm. Air near the ground is forced to move inward to the center of the circulation — this is known as convergence. Continue reading

Category: Phenomena, Seasons, Severe Weather

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What are the leading threats from hurricanes?

With all the news about hurricanes over the past couple of weeks we’ve been asked a lot of questions about the various threats posed by these storms.

Hurricane Harvey is a clear example of the damage that long-duration heavy rains can inflict. Hurricane Irma provides an example of the destructive power of the winds associated with these storms. Continue reading

Category: Severe Weather, Tropical, Weather Dangers

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Why is lightning white?

Lightning is a huge electrical discharge.

Static charges form in a storm composed of ice crystals and liquid water drops. Turbulent winds inside the storm cause particles to rub against one another, causing electrons to be stripped off, making the particles either negatively or positively charged. Continue reading

Category: Meteorology, Phenomena, Severe Weather

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Is UW-Madison involved in hurricane forecasting?

Hurricane Harvey is the first hurricane to make landfall in the United States since Wilma hit Florida in October 2005.

Harvey made landfall early Saturday morning as a Category 4 storm with estimated sustained winds of 130 mph and gusts to 150 mph. Continue reading

Category: Meteorology, Severe Weather, Tropical

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Can weather fan the flames of revolution?

July was the month of revolution in both America and France in the late 18th century as we declared independence from Britain on July 4, 1776, and the French Revolution began with the assault on the Bastille in Paris on July 14, 1789. It is interesting to examine the extent to which weather may have influenced the passions that led to these seismic events.

The author of our Declaration, Thomas Jefferson, was such an avid weather observer that he brought his instruments with him from Monticello to Philadelphia that summer. He recorded a mild day on July 4 with a high temperature of 76 degrees. Phineas Pemberton, a prominent citizen, independently recorded the same high temperature – nearly 10 degrees Fahrenheit below normal. Pemberton also noted a wind shift from northerly to southwesterly with a falling pressure as often accompanies passage of a surface high-pressure system. Thus, the great revolutionary act in America was birthed in benevolent weather conditions. Continue reading

Category: Meteorology, Severe Weather

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