Using the daily change in the Southern Oscillation Index to develop analogues and the relationship to severe weather outbreaks

Abstract

The occurrence of severe weather is an annual problem for much of the United States and North America and maximizes from March through June. With the increased interest in subseasonal weather forecasting, there have been attempts to anticipate the occurrence of anomalous weather on the timescale of one to 4 weeks including the occurrence of severe weather. Previous research has shown that teleconnection indices, associated with long period Rossby wave activity, or persistent large-scale flow regimes have been useful tools in this endeavour. Here, abrupt changes over a 24–72-hr period (10 or more units per day or 20 or more units over 3 days) in the Southern Oscillation Index (SOI) time series will be used to demonstrate that these changes can be associated with the possible occurrence of major severe weather event-days defined as; 20 or more tornado, 155 or more wind speed events >25.9 m·s⁻¹, or 135 or more hail diameter larger than 25.4 mm, reports over the United States one to 3 weeks in advance, especially during the March through June period. The severe weather events obtained from the archive at the Storm Prediction Center (SPC) from 1991 through 2020 were used. The results here demonstrate that more than 7 in 10 major severe weather occurrences were associated with abrupt positive and negative changes in the daily SOI when using signal detection methods.