April 27, 2011: Predicting a Tornado Outbreak with Unpredictable Consequences

Forecasts leading up to the deadliest tornado outbreak in over 35 years will be reviewed as a part of this retrospective on recent events across the southern United States. More tornado fatalities occurred on this day (317) than were attributed to the infamous April 1974 Super Outbreak (315). The review of meteorological information will include a look at the large scale pattern leading up to the outbreak and the model guidance that was used by forecasters at the Storm Prediction Center (SPC) to gain confidence in the potential for a severe weather outbreak across the South. In the days leading up to the outbreak, forecaster confidence in the scenario was reflected in the severe weather probabilities used in SPC outlooks. The wording of those outlooks also became more dire and threatening. Some of the strongest wording and highest probabilities for tornadoes were reserved for day of the outbreak when all the meteorological conditions came together to result in a very dangerous and deadly day across five southern states.

Despite the excellent forecast lead time for this historic tornado event, many still died. This presentation will conclude by discussing the historical context of the high death toll in this event, as well as the incredibly high mortality (141 dead) from a single EF5 tornado, in Joplin, Missouri, less than a month later.