Granite Geek: We're Overdue For A Tornado

Apr 28, 2015

The Granite State gets lots of “weather”—and by weather, we usually mean snow. This winter we saw a lot of it. What we don’t see a lot of? Tornadoes! All of the New England states get about seven per year on average. But one meteorologist says we’re due for one soon. David Brooks has been writing about tornadoes this week in his weekly Granite Geek science column for the Nashua Telegraph.

David, you spoke recently with a meteorologist who says we’re “overdue” for a tornado. That sounds kind of scary. Should we be scared?

No, we should not be scared. Spending your life being scared is not helpful. I talked to Glenn Field. He’s a meteorologist with a really cool title: “Warning Coordination Meteorologist” with the National Weather Service down in Taunton, Massachusetts. And I called him up to talk to him about tornadoes partly because this is “America Prepared Action Week” which is a national program trying to get emergency folks and others to think about preparing for dangers. And one of the things they’re talking about is tornadoes. There are a number of programs in Nashua this week. Frankly, I didn’t really think of tornadoes as being a big deal here. We have one every three years in Hillsborough County.

When was the last time we had a serious tornado in New Hampshire?

We had a big one in 2008 that lasted for about 50 miles on the ground, which is, according to the data I can find, about three times the previous length. It destroyed a lot of homes. And, of course, down in central Massachusetts—Worcester and towns around Everett—had two tornadoes last year that did quite a lot of damage. Hundreds of thousands, millions of dollars of damage. The one in New Hampshire had one fatality. When they come, they can be very bad, but they don’t come very often.

Why are they so prevalent in the Midwest and not so prevalent in the northeast? I imagine it has something to do with our geography.

Tornadoes usually form when there’s a discontinuity in the sense of there’s one large, wet air mass hitting a dry one and a difference in temperature. And that creates the sort of energy that can be turned into a twister, particularly if there are winds going in different directions at different altitudes. Frequently the wind is blowing at a different direction a half mile up than it is on the ground. That can create a twister.

We have dry air that comes down on the leeward side of our mountains, so when air goes up, it gets pushed up one side of the mountain. Usually it’s coming from the west, so it gets pushed up the western side of the mountain, and the air gets colder so it drops precipitation because cold air can’t hold as much moisture. And so when it comes down the other side of the mountain it doesn’t have much moisture in it so it’s dry.

What happens in the Midwest is that that air comes off the Rocky Mountains, so it’s really quite dry, and it hits the wet air coming in from the gulf of Mexico. We have some dry air off our mountains that can hit wet air coming off the Atlantic ocean, but it’s nowhere near the level we see in the Midwest.

You also mentioned the Coriolis Effect. What’s that?

It’s one of my all-time favorite things that happens on the earth. Because the earth is spinning, the winds go different speeds at different latitudes, so if you have a large air mass it can be made to turn, and of course in the northern hemisphere. That’s why you always see hurricanes spinning in the same direction and they spin the oppose direction in the southern hemisphere.

The thing that most people know about the Coriolis effect that isn’t true is that it also causes the water in your toilets to turn in a certain direction in the southern hemisphere, with the implication that as you cross the Equator, the water as you flush the toilet will be spinning one way, it’ll stop and start spinning the other way. Unfortunately, that’s not true. I would be very cool if it was. The Coriolis Effect is not strong enough to alter the water in something as small as your toilet bowl. If you had a toilet the size of Winnipesaukee, then I imagine the Coriolis Effect would apply.

And your sources also mentioned that we may also want to worry about hurricanes. Why is that?

For the same reason is that we’re historically overdue. The last hurricane that really effected the Nashua area, this part of the state, was Bob, which was almost a quarter century ago. So we are way overdue for another one that will effect us. Of course, weather doesn’t happen on a regular schedule, so the fact that we’re overdue doesn’t mean it’s going to happen, but better safe than sorry.

Read David's full article here.