June 2, 2018 – Preliminary data from NOAA’s Storm Prediction Center indicate that the U.S. had a record low number of tornadoes

The spring severe weather season for the U.S. (March – May) is finally over. We had 449 EF0 – EF5 tornadoes from Jan 1 to June 2, which is a record low number for the period and certainly well below the historical average during 2005 – 2015 (792). Recent studies have suggested that U.S. tornado activity in spring season is influenced by tropical Pacific sea surface temperature condition, which is known as El Nino – Southern Oscillation (ENSO). A weak La Nina (i.e., cold sea surface in the eastern tropical Pacific) developed in the tropical Pacific around September 2017. However, the tropical Pacific returned to ENSO-neutral during April 2018. Given that ENSO’s impact on U.S. tornado activity is largely in April, it is probably safe to say that the 2017 – 2018 La Nina terminated too early to influence this year’s tornado season in the U.S. So, what is behind a record low number of tornadoes in the U.S. this year? Probably, we should thank the unpredictable weather for it.

http://www.noaa.gov/news/us-is-having-incredibly-quiet-tornado-season-so-far

http://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

http://iopscience.iop.org/article/10.1088/1748-9326/11/4/044008

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0783.1

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