Tornado's intensity rare occurrence for November

INDIANAPOLIS -- The deadly tornado that obliterated homes across a swath of southwestern Indiana was unusually intense and fast, packing winds that topped 200 mph as it roared through the night at up to 75 mph, meteorologists said Monday.\nThe storm's strength, its 41-mile path of destruction and the fact that it struck in the middle of the night in November are all unusual, said Dan McCarthy, warning coordinator at the National Oceanic and Atmospheric Administration's Storm Prediction Center in Norman, Okla.\nSunday's twister, which killed 23 people including an unborn child, was at its peak a strong F3 on the Fujita scale, with winds that reached or exceeded 200 mph, according to National Weather Service estimates.\nThat makes it the strongest and deadliest November tornado since an F4 twister with winds of 207 to 260 mph killed two people in Van Wert, Ohio on Nov. 10, 2002, McCarthy said.\nPushed by a rapid shift in the jet stream along a strong cold front, the tornado raced along at 70 to 75 mph and stayed on the ground for about 35 minutes, said David Blanchard, a meteorologist with the National Weather Service in Paducah, Ky.\n"It was just booking along during the greatest punch of the jet stream. You just don't see speeds like that very often," Blanchard said.\nWeather service meteorologists who surveyed the damage and path of the tornado Sunday and Monday estimated its winds reached between 170 and 180 mph as it plowed through the Eastbrook Mobile Home Park southeast of Evansville, killing 18 people, he said.\nA few miles to the northeast, its winds peaked at 200 mph or greater near the Warrick County town of Paradise, Ind., with the path of destruction about a quarter-mile wide, Blanchard said.\nAlthough most people think of tornadoes as spring events, the nation actually experiences a "second season" of tornadoes from mid-October through November, when shifting weather conditions resemble those in the spring, said McCarthy of NOAA.\n"That's what makes tornadoes so dangerous this time of the year -- people just don't expect them. They expect them to happen in the spring and in the afternoon or evening, not at two in the morning in November," he said.\nAbout 75 percent of twisters occur in the March to June period, but another 10 to 12 percent occur during late October and November as the jet stream shifts southward, shoving warm, moist southern air against cold, dry northern air as occurs in the spring, McCarthy said.\nSunday's deadly storm arose as a strong cold front collided with the abnormally warm air that has held sway over the nation's midsection this fall, Blanchard said.\nIt was spawned by a supercell thunderstorm that originated over Cape Girardeau, Mo., and moved across southern Illinois and into northwestern Kentucky.\nThe twister began about 1:50 a.m. CST near Smith Mills, Ky., jumped the Ohio River into Indiana's Vanderburgh and Warrick counties, destroying or severely damaging more than 100 homes before it dissipated in Spencer County just southwest of the town of Gentryville after a 41-mile journey.\nUntil Sunday's deaths, this year, the United States had experienced some of the fewest tornado fatalities in several years, with only 10 deaths from seven killer tornadoes, McCarthy said.\nAnd for the first time since record-keeping started in 1950, no one was killed by a tornado in April, May or June, he said.