by Chuck Gaidica
In the past few months we have seen devastating tornado outbreaks and flooding across the southern United States. Michigan had plenty of thunderstorms, but nothing like the killer storms down south.
Weather coverage has emerged as one of the top reasons why people watch local television news. We in the forecasting business have known for a long time that weather is one of the few things to affect everybody, everyday.
Here in Michigan, we have a unique challenge. We have to forecast the weather with the same tools and forecast models as other meteorologists in the country, but we get the added challenge of the Great Lakes. These wonderful bodies of fresh water help to create and divert weather patterns. Most of us associate lake effect with enhanced snowfall, but the Great Lakes can also have an impact on temperature patterns, wind direction and more.
This time of the year our focus shifts to thunderstorm development and severe weather. Tornadoes and their potential for destruction are of great concern. We live in a state with active, severe weather patterns. In fact we live on the northern fringe of what is called "tornado alley."
Even though tornado alley is a phrase usually used to describe parts of the mid-south, Midwest, plains and Ohio valley, the statistics show Michigan (especially southern-lower Michigan) can also be filled with tornado activity.
According to the National Weather Service, Michigan averages 16 tornadoes per year. Since 1950, every one of Michigan's 83 counties has experienced at least one tornado. The peak season for tornadoes in Michigan is April through August. Although tornadoes can occur at any time of day, they usually strike between 3 p.m. and 9 p.m., which is usually the peak of daytime heating, often an ingredient in the storm development process. The average tornado in Michigan is on the ground for less than 10 minutes and travels about five miles.
But there are exceptions. A large tornado that struck Louisiana and Mississippi in April was on the ground for nearly 159 miles and approached a width of two miles. That would be like a tornado staying on the ground in Michigan from Detroit to Mt. Pleasant, carving a path of destruction nearly two miles wide. It is hard to imagine, but it happened.
A tornado is produced by a severe thunderstorm. A complicated bunch of ingredients come together to create a violent, rotating wind that extends from a thunderstorm. It is not uncommon for the rotation to start horizontally along the ground and extend vertically into the thunderstorm cell.
If this rotating column of air doesn't touch the ground it is called a funnel cloud. If it touches the ground it becomes a tornado. If it touches water, it is called a water spout.
Any of the above, whether seen in person or spotted on radar, are enough for the National Weather Service to issue a tornado warning.
A tornado watch is issued when conditions are "right" for tornadoes in and around the watch area. You get the most lead time with a watch. Many times the sky is still blue when a tornado watch is issued, but this is a time to keep your eye on the sky.
A tornado warning is issued when a tornado has been spotted on radar or in person. A warning requires immediate action. Tornadoes generally travel at 30 mph but have been known to move as fast as 70 mph.
When you hear of a warning from the media or local sirens sound, it is time to seek shelter. You should move quickly indoors and go to the lowest, centermost part of your home or building, preferably a basement. Stay away from outside walls and windows. Tornadoes are intense areas of low pressure. That means along with ferocious winds, the storm itself can cause damage just because of the relative pressure difference inside your home.
One effective way to receive warnings is through a battery powered NOAA Weather Radio with an alert function, which can receive alerts from the National Weather Service. They are available from several manufacturers and sell for about $30.
We see video on television and the web of people with a camera getting stills or video of severe storms. If you are close enough to record a storm or tornado on camera, you are in the wrong place. You need to get to a safe and sturdy part of the house and fast!
Even when we take cover, and the storms pass with little trouble, there can be a cost.
In 2009, Michigan had the quietest severe weather season since Doppler radar came into wide use in our state. Even though the season was quiet on average, a few key storm events cost us plenty. They weren't tornadoes but they were expensive storms. Flood damage in Michigan for 2009 cost us nearly $77 million dollars, while damage from severe storms cost us another $150 million dollars.
Chuck Gaidica is director of meteorology at WDIV in Detroit.