The USA in the past 12 months has seen the fewest number of tornadoes
since at least 1954, and the death tolls from the dangerous storms have
dropped dramatically since 2011.
Just two years after a ferocious
series of tornado outbreaks killed hundreds of Americans, the USA so
far this year is enjoying one of the calmest years on record for
twisters. Through Thursday, tornadoes have killed only three Americans
in 2013; by the end of May 2011, 543 Americans had died.
The seven
people killed from May 2012 to April 2013 is the fewest in a 12-month
period since five people died in September 1899-August 1900, according
to Harold Brooks, research meteorologist with the National Severe Storms
Laboratory in Norman, Okla.
The year-to-date count of tornadoes
is probably approaching the lower 10% of all years on record, said Greg
Carbin, warning coordination meteorologist with the Storm Prediction
Center in Norman.
The reason: An unusually cool weather pattern
from the Rockies to the East Coast. "Generally, the lower the
temperature and/or the drier the air, the lower the number of
thunderstorms," said AccuWeather meteorologist Alex Sosnowski.
Severe thunderstorms produce tornadoes, along with large hail and high winds.
So
far in May — usually the USA's most active month — only three tornadoes
have formed. All have been rated EF-0 on the Fujita scale of tornado
intensity. EF-0 is the weakest rating for tornadoes, with wind speeds of
about 65-85 mph.
The EF-5 tornado that ravaged Joplin, Mo., two years ago, had estimated wind speeds as high as 250 mph and killed 158 people.
The
record low in tornadoes comes less than two years after a record high
from 2010 to 2011, Weather Underground meteorologist Jeff Masters said.
"The extraordinary contrast underscores the crazy fluctuations we've
seen in Northern Hemisphere jet stream patterns during the past three
years," he said. "Call it 'weather whiplash' of the tornado variety."
Current
weather patterns are expected to continue into the first part of
summer, likely keeping 2013 well behind the curve for violent
thunderstorms and tornadoes, AccuWeather reports.
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