Watch Those Funnel Clouds

Q: Is there a difference between a funnel cloud and a tornado?

A:  It’s all in the timing, says Brent McRoberts of Texas A&M University. A funnel cloud is a powerful twisting mass of air stretching down from a thunderstorm, but it has not yet touched the ground. “Once it makes contact with the ground, it’s then officially called a tornado,” McRoberts explains. “That means that a funnel cloud has become a tornado. A funnel cloud doesn’t do much damage up in the air, but once it makes contact with the ground, that’s when trouble starts. If a funnel cloud is spotted, it should be treated like it is a tornado because the situation can change quickly and become a life-threatening event.”

A funnel cloud about to touch the ground. Photo: Shutterstock

Q:  Once it does touch the ground, how fast can it travel?

A:  Most tornadoes travel fairly slowly, at about 20 miles per hour or so, McRoberts says. “But some have been clocked at 60 to 70 miles per hour. You have to realize that the winds inside the tornado are much faster than the rate at which the storm moves on the ground. Winds inside a tornado can reach 300 miles per hour, which is why they cause so much destruction and death. In any year, there are about 100,000 thunderstorms in the United States, and these produce about 1,000 tornadoes every year. Some travel just a few hundred feet, while others have been known to travel more than 100 miles on the ground. Studies show that the average tornado will travel a little over 3 miles on the ground.”

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Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.

Floods Are The Deadliest Weather Disaster

Q: What is the deadliest type of weather disaster?

A: The weather-related incident that kills the most people in the United States is flooding, says Brent McRoberts of Texas A&M University.  “You hear a lot about blizzards or tornadoes, but more people are killed by floods than any other type of weather-related incident,” he explains.  “This goes back to 1889 and the famous Johnstown Flood in Pennsylvania in which 2,200 people were killed.  During the 20th century, floods were the number one natural disaster in the U.S. in terms of property damage and fatalities. In 1993, the Great Midwest Flood killed 48 people and did $12 billion in damage in numerous states.  But that’s nothing compared to other parts of the world.  In 1931, one of the worst weather incidents in history occurred when the Yangtze River flooded, killing 3.7 million in China in flooding and subsequent disease and starvation. In 1971 in Vietnam, more than 100,000 died in flooding in that country.”

Q: Why are floods so dangerous?

Flash floods can be killers

A: The best answer is that too much water flows at one place in a very short time, adds McRoberts.  “Flash floods are the most dangerous because they can happen quickly and have tremendous power, moving anything in their path,” he says.  “Flash floods can occur any time, any where. The National Weather Service notes that flash floods can occur because of excessive rainfall, a dam or levee failure or a sudden release of water held by ice jams.  A flash flood caused by 15 inches of rain in 5 hours killed 237 people in Rapid City, S.D., in 1972.  According to the U.S. Geological Survey, most flood deaths are caused by flash floods, and 50 percent of all flash flood fatalities are vehicle-related.  Also, 90 percent of people who die during a hurricane are due to drowning caused by flooding.  To compound the problem, in the U.S. most homeowners insurance policies do not cover damage caused by flooding.”

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Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University

Winds Often Die Down At Night

Q:  Why does the wind seem to die down at night?

A:  The simple and quick answer is that there’s no sun, says Brent McRoberts of Texas A&M University.  “Wind is a form of energy and it gets much of its strength from the sun,” he explains.  “You can think of wind as a huge river of air over land, and it does this day or night.  But as the sun rises and starts heating up the ground, rising warm air mixes with slower air near the ground and with air moving faster that is above ground.  This faster-moving air is pushing downward, and it creates windy and breezy conditions as the day progresses.”

Winds tend to die down at night. Photo: Shutterstock

Q: So what happens at night?

A:  When the sun starts to set, this mixing of conditions doesn’t happen as much, so the winds start to slow and eventually die down.  “Remember that hot or warmer air expands and rises,” McRoberts adds.  “At night, the ground begins to cool.  Air closer to the ground cools by radiation, so there is a lack of heat and energy and these directly affect air currents. So the winds at night and in the early morning hours are usually the weakest.  But remember that cold fronts and storms can occur and these directly affect wind speed, too.”

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Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.

Heat Bursts Mean Very Hot Air

Q: What is exactly is a heat burst?

A:   It is an odd weather occurrence that happens during thunderstorms when temperatures can quickly rise 25 degrees or more in just a few minutes, says Brent McRoberts of Texas A&M University.  “Heat bursts usually happen in the evening,” McRoberts explains.  “It is a strong burst of hot air that is pushed down very quickly and is warmed all the way down to the surface, often originating from 20,000 feet or more.  When the air reaches the ground, it is very hot – in some cases well over 100 degrees.  Heat bursts are odd because usually during thunderstorms, the air will become cooler. The air in a heat burst is not only very warm, but it is very dry and sometimes this hot, dry air can create damaging winds in excess of 75 mph.”

Heat bursts usually happen in the evening

Q: How much can the temperature rise during a heat burst?

A: There have been some amazing documented examples of rising temperatures caused by heat bursts, McRoberts adds. “In 1993 in Glasgow, Mont., the temperature was recorded at 67 degrees at 5:02 p.m. during a thunderstorm.  By 5:17 p.m. – just 15 minutes later – the temperature had shot up to 93 degrees.  In 1960, a reported heat burst in Bosque County, Texas briefly raised the temperature to a mind-boggling 140 degrees.  The intensity of a heat burst depends on the size of the thunderstorm and how much the air can heat up before descending down to the ground.”

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Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University

Troughs and Ridges Can Affect Your Weather

Q: You often hear about a “ridge” and a “trough.” What are they?

A: Both terms refer to conditions in the air, says Brent McRoberts of Texas A&M University.  “Air is usually associated as being part of a mass that is high pressure or low pressure,” he explains.  “A trough is an area of low pressure, either at the surface or higher aloft.  A ridge is just the opposite – it refers to a high pressure air mass. Both of these can tell us a lot about the weather in a particular area.”

Troughs and ridges can affect the weather. Photo: Shutterstock

Q: How is that?

A:  The type of air can often determine if it’s going to be a nice day or stormy one, McRoberts says.  “Usually, strong ridges are accompanied by warm and dry weather conditions at the surface,” he says.  “On the other hand, strong troughs are often preceded by stormy and sometimes violent weather conditions. A strong upper air trough can often push a cold front through. So it’s a good idea to notice where ridges and troughs are because they can affect the weather where you live.”

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Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.