August 2014 Brings Lowest U.S. Tornado Count Since the 1960s
By Jon Erdman
Published: September 1, 2014
The August 2014 tornado count in the U.S. was the lowest since at least the 1960s.
In preliminary data compiled by The Weather Channel severe weather expert, Dr. Greg Forbes, and NOAA's Storm Prediction Center, only 27 tornadoes were reported in the U.S. this August.
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If that preliminary tornado count holds, it would be the least tornadic August in 51 years, when only 26 tornadoes were observed in August 1963. The last August with fewer than 30 tornadoes nationwide was 1967.
Doppler radar, spotter networks, storm chasers, the internet, smartphones and social media have lead to better detection of weaker tornadoes (EF0, some EF1) today, compared to past decades. This is what makes low tornado counts in the modern era compared to the 1950s and 1960s impressive.
Why So Few Tornadoes?
Despite being in the heart of summer, August is not typically an active month for tornadoes.
As you can see in the bar graph at right, only 81 tornadoes are sighted in August on average, less than each month from March through July, and slightly below that of September.
Typically by August, the polar jet stream migrates into Canada, taking most of the deep-layer wind shear required for supercell thunderstorms most often to the Canadian prairies.
What made August 2014 particularly quiet for tornadoes?
- No U.S. tropical cyclone landfalls: One prime tornado-generator in the months of August and September is a landfalling tropical storm or hurricane. Both Hurricane Bertha and Hurricane Cristobal steered well east of the U.S. in August.
(MORE: 5 Most Tornadic Hurricanes)
- Cool, dry air intrusions: While not the magnitude we saw in July, several frontal boundaries were able to sag quite far south for August, ushering in drier, if not cooler air as far south as the Gulf Coast.
- Flooding: Slow-moving weather systems across the U.S., particularly one in mid-August, lent themselves more to flooding rainfall (Detroit, Baltimore, Long Island, north Phoenix) than discrete supercell thunderstorms spawning tornadoes.
August continues a trend of relatively few tornadoes so far in 2014.
Again, using preliminary data, year-to-date tornado counts are pacing about 35 percent, or roughly 376 tornadoes, below the 10-year average-to-date through August 30, according to Dr. Forbes.
Weather map and data guru Daryl Herzmann from the Iowa Environmental Mesonet tabulated all National Weather Service severe thunderstorm and tornado warnings issued since 2002 in the graph below. Note only 2002 saw fewer warnings issued year-to-date.
Only June (preliminary count: 331) has featured an above-average tornado count of all eight months in 2014.
March 2014 was the second straight March with less than 20 total U.S. tornadoes. April followed with only half that month's average tornadoes (113).
Just as a hurricane season with few named storms and hurricanes can spawn one or two destructive storms, destructive tornadoes and tornado outbreaks have occurred in 2014, despite the low tornado counts. Perhaps first and foremost were the Pilger, Nebraska, twin tornadoes in June 2014.
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