Sunday, May 11, 2008

Are tornados in the Mid Atlantic more common now with global warming?



Are storms stronger now in the mid-Atlantic states than they used to be? Is it because of global warming?

I can speak anecdotally. When I was growing up in the DC area in the 50s and 60s, I recall that most severe thunderstorms occurred after hot humid days with cold fronts. Severe, lightening generating storms and tornado watches did not occur except on hot days. There were rare exceptions, such as “thunder snow” with big Noreasters in the winter, as with the 1961 Inauguration Day blizzard.

In the past few years, we have seen much more tree damage, a tendency for much stronger pull-away winds after cold fronts, and much more dangerous storms during “ordinary” lows that pump in large amounts of Atlantic moisture. The tornados in Suffolk Va a couple weeks ago, and in Stafford County VA Thursday night occurred during “ordinary” lows passing to the north or west, with southeast winds at the surface, and cold-front-like winds from the northwest in the upper levels, resulting in spin, even when surface temperatures were only in the 60s, even at night when the sun had not been out to heat up the ground. I don’t recall this occurring before.

I’ve noticed that southern Maryland, between the Potomac River, Bay, and Ocean gets much more violent weather than the No VA suburbs west of Washington. That area got tornados even in “wrong direction” thunderstorms moving from the Southeast during a stalled low. “Wrong direction” fronts are becoming more common as land lows take on tropical storm characteristics, even in the spring. However, that area is flatter, surrounded by warm water, and farther from the mountains. Some parts of the DC area to the west are somewhat protected by the closer Blue Ridge, especially the Central Section that rises to 4000 feet. A bit farther north, the mountains are lower, so Montgomery County MD seems less “protected.”

Thinks have changed. The tree foliage stock, important for absorbing carbon, has gotten older and weaker, and a lot of it fell in 2003 during Isabelle, which never actually got violent; it was just prolonged and the ground was soaked.

When I was a graduate student a Kansas University 1966-1968, a few times some of us rode around chasing tornadoes. I knew a woman who lived through the Wichita Falls, Texas tornado of 1979, while working in a fast food restaurant that was struck. This was called a "wedge tornado." And I recall the March 30 tornadoes in Minnesota in 1998; I was with a friend driving back to Minneapolis from a visit to the wineries up north when the violent storms struck suddenly.

On August 11, 2001, I spotted a funnel cloud when driving back from Rehoboth Beach , DE, along route 9; flooding thunderstorms had occurred, emptying the beach. I was probably about a mile from it. It didn't hit any buildings, just farmland.

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