Extended U.S. Tornado Outbreak During Late May 2019: A Forecast of Opportunity. Issue 16 (27th August 2019)

• Record Type: Journal Article
• Authors: Gensini, Vittorio A.; Gold, David; Allen, John T.; Barrett, Bradford S.
• Is Part Of: Geophysical research letters. Volume 46:Issue 16(2019)
• Page Start: 10150
• Page End: 10158
• Publication Date: 2019-08-27
• Subjects: tornado -- forecasting -- subseasonal -- weather -- extreme -- spring; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL084470
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The second half of May 2019 was an unusually active period for tornadic thunderstorms across the U.S. Great Plains, Midwest, and lower Great Lakes. While this period typically coincides with the peak climatological frequency of tornadoes, preliminary reports of tornadoes were over triple the expected 30‐year average. Multiple‐day outbreaks of tornadoes are not unprecedented in the United States; however, this event was perhaps the first to be forecast at subseasonal lead times (3–4 weeks) by the Extended Range Tornado Activity Forecast team. This forecast of opportunity was driven, in part, by anomalous convective forcing in portions of the tropical Indian and Pacific Oceans, causing subsequent changes in Northern Hemisphere atmospheric angular momentum. This manuscript analyzes the evolution of hemispheric‐scale circulation features leading up to the event, examines teleconnection processes known to influence U.S. tornadoes, and provides insights into the forecast process at subseasonal lead times. Key Points: Tornado frequencies during the last half of May 2019 were over three times the climatological average This extended period of favorable tornado conditions were successfully forecast nearly 4 weeks in advance Changes in atmospheric angular momentum associated tropical convection appear to have created this forecast of opportunity