For the second consecutive year, U.S. March tornado counts are among the lowest on record.
March U.S. Tornado Stats
March U.S. Tornado Stats
A preliminary 21 tornadoes touched down across the nation in March.
If this sounds familiar, March 2013 was the least tornadic March in 35 years, with only 18 tornadoes.
March continues a slumbering tornado trend for the year. A preliminary 66 tornadoes have been tallied in 2014 as of April 1; this is just over one-third of the 10-year average-to-date of 186 tornadoes.
"Twenty other years since 1950 had fewer tornadoes (than 2014) through March 20," says Forbes. "There had been just eight tornadoes thus far in 1969. The 41 tornadoes in February 2014 have kept the year from being closer to a record-low pace."
The dominant weather pattern in place through the first two-plus months of 2014 helping to squelch tornadoes in the U.S.
Why the Tornado Drought?
Essentially the same pattern responsible for a persistently cold and snowy winter in parts of the U.S. also, for the most part, squashed the threat of severe weather through the first three weeks of March.
A pronounced southward dip in the polar jet stream has frequently driven cold air into the Gulf of Mexico, as a powerful northward diversion of the jet stream has persisted in the eastern Pacific Ocean and western U.S. This is the polar opposite of a pattern which would favor severe weather in the southern states during winter.
As a result, deeper, richer Gulf moisture can't flow northward into the southern U.S. ahead of a strong jet-stream level disturbance. Shallow, meager moisture, with weak instability lends itself to damaging straight-line winds in any severe thunderstorms that have developed, rather than tornadic supercells.
However, history shows that a slow start to the year doesn't signal a quiet period is ahead. Both 2012 and 2013 featured at least 400 less U.S. tornadoes than the 10-year average. Despite that apparent tornado drought, we had the following destructive events:
- Mar. 2-3, 2012: EF4 in Henryville, Ind.; EF3 in West Liberty, Ky.
- May 15, 2013: EF4 in Granbury, Texas
- May 19-20, 2013: EF5 in Moore, Okla.
- May 31, 2013: EF3 in El Reno, Okla.
- Nov, 17, 2013: EF4 in Washington, Ill.
How long can 2014 stay quiet?
Average monthly U.S. tornado count from 1984-2013. Note the sharp increase from March into April.
The Spring Ramp-Up Looms
As you can see in the bar graph at right, on average, the U.S. witnesses a marked ramp-up of tornadoes in April as warmer, more humid air flows farther north to intercept under the still-energetic polar jet stream.
A corridor from the southern Plains to the Tennessee Valley is typically in the highest risk for severe thunderstorms in early April, however, those are just climatological averages. Early April severe weather can stretch into the Upper Midwest, Ohio Valley and even parts of the East.
(MORE: 10 Worst U.S. Tornado Outbreaks)
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MORE: Marysville, Ind. Tornado (Mar. 2012)
Tony Sherrard searches through debris that used to be his home for family keepsakes, March 3, 2012 in Marysville, Indiana. (Scott Olson/Getty Images)