Popular weather vendor AccuWeather this week took the meteorological community by storm when it released a highly specific outlook showing how many tornadoes — despite their notorious unpredictability — will be seen in the United States in 2019.
“AccuWeather predicts there will be 1,075 tornadoes in 2019,” the company told the public, after first releasing the outlook to its paying clients including television stations and newspapers.
AccuWeather predicted that traditional tornado-alley places — Oklahoma, Kansas, Texas and southern Nebraska — have the highest risk of twisters this spring. It shows that almost all of Iowa is expected to have “isolated” tornadoes in keeping with the three-year average — although western and southwestern Iowa could see an elevated “moderate” risk.
“The 525 tornadoes expected from March through May is almost exactly the normal average of 526 from March through May,” AccuWeather wrote.
In other words, the company expects one fewer tornado than average in the spring. Many broadcast and private-sector meteorologists took issue with that.
“They are simply being very unscientific,” wrote Scott Feldman, a meteorology graduate from Iowa State University. “There is really no way to know ... until a few days before a severe outbreak. It misleads the public into thinking we know more than we do so far in advance.”
He said such predictions undermine public trust in meteorologists.
Iowa’s storm season illustrates the difficulty in arriving at a specific number for just how many tornadoes will hit. Within the last five seasons, Iowa saw 88 tornadoes in 2014 but fewer than half that — 43 — in 2016. The state saw 69 tornadoes — about midway between the five-year low and high — in the 2018 season. Those included the strongest storms of the year — EF3 — that on July 19 struck Pella and Marshalltown.
Writes AccuWeather of its rationale: “We believe warmer-than-normal sea surface temperatures over the Gulf of Mexico will lead to increased moisture transport from the Gulf over the region and ultimately a higher frequency of severe weather in these areas.”
Feldman noted warmth and moisture are among many ingredients needed to spin up a tornado, and there is little correlation between sea surface temperatures in April and May and tornado frequency in Oklahoma.
Among the leaders in the field of advanced tornado forecasts is John Allen, assistant professor of meteorology at Central Michigan University. He co-authored a paper in 2015 linking U.S. tornado counts to the El Nino/La Nina phase.
While “guidance ... is feasible at leads up to 5 months,” the article notes “substantial variability ... that may not be explainable.”
“I am extremely skeptical of Accuweather’s decision to include a precise number of tornadoes in their forecast,” Allen wrote to the Washington Post. “There is no basis for such precision, as seasonal tornado counts are extremely difficult to predict.”
Allen names a number of factors that influence seasonal tornado tallies, including El Nino, Pacific and Atlantic sea surface temperatures and seasonal wind shifts.
“For the upcoming season, there is a weak El Nino event ongoing, which typically would imply the unstable conditions favorable to tornadoes being less likely over the Great Plains,” Allen said. “In contrast, the Gulf of Mexico is exceptionally warm, which would instead suggest more instability to be available over the U.S. Taken together, this suggests a forecast of mixed signals at best.”
A number of meteorologists urged AccuWeather to “show their work” to explain the science behind its prediction. AccuWeather declined, saying it is a private company and that its methods were proprietary.
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In a statement, the Pennsylvania company said “AccuWeather is really proud of its 2019 tornado forecast. We have been in the prediction business for 57 years and have found that the powerful combination of utilizing all the tools and reliable indicators available, including the expertise of our over 100 expert meteorologists, results in predictions with the greatest accuracy.”
The Washington Post contributed.