Dangerous 'High Risk' Midwest U.S. Tornado Outbreak Underway

A rare and very dangerous late-season severe weather outbreak is underway over the Midwest U.S., where NOAA's Storm Prediction Center is predicting a "High Risk" of severe weather--their highest level of alert--over most of Indiana and Illinois, plus portions of Southern Lower Michigan and Western Ohio. This is just the second "High Risk" forecast for 2013, and the area at risk of severe weather is unusually large. According to a list of all "High Risk" forecasts issued since 1984 maintained at Wikipedia, today's High Risk area is the farthest north such a forecast has been issued so late in the year. A 992 mb low pressure system that was over Northern Illinois on Sunday morning will move northeast and rapidly intensify to 965 mb by Monday morning, dragging a strong cold front across the "High Risk" area on Sunday afternoon. Isolated supercell thunderstorms--the kind most likely to produce strong and violent tornadoes--are expected to form ahead of the front, and the SPC is expecting multiple long-track strong tornadoes to form during the early afternoon. Any tornadoes that form will be moving at highway speed--50 to 60 mph--and will be under low cloud bases around 2,000 feet, making these storms difficult to see and react to, particularly in wooded or hilly areas. If the sirens sound, seek shelter!


Figure 1. Severe weather outlook for Sunday, November 17, 2013.

A dangerous day in Chicago
Most of Illinois, including Chicago, has been placed under a special "PDS" Tornado Watch: a "Particularly Dangerous Situation." Severe thunderstorms spawning tornado warnings have already erupted over Southern Wisconsin and Western Illinois as of 10:15 am CST. Severe thunderstorms are likely to sweep through Chicago in the early afternoon during today's Ravens - Bears game, which starts at noon CST. According to NBC 5 in Chicago, loose objects are being removed from the stadium in anticipation of high winds, and officials are prepared to evacuate fans, if necessary. An NFL game will stop if there is lightning, and cannot continue until 30 minutes afterwards.


Figure 2. Prior to Sunday's severe weather outbreak, there were seven billion-dollar weather disasters in the U.S. in 2013. Five of these disasters were severe weather outbreaks--the third highest such total in history.

A slow but very expensive tornado season
It's been an unusually slow severe weather season, with the 2013 preliminary tally of 818 tornadoes the lowest year-to-date count since the extreme drought year of 1988. However, when severe weather outbreaks have come, they have been unusually destructive. According to Aon Benfield, there have been five severe weather outbreaks topping $1 billion in damages this year. This is the third highest number of such disasters on record, going back to 1980. The record is shared by 2011 and 2012, with seven billion-dollar-plus severe weather outbreaks, according to NOAA's National Climatic Data Center. The total damage from 2013's five billion-dollar severe weather outbreaks is $14 billion, which is the third highest on record, behind 2011 ($29.6 billion) and 2010 ($16.3 billion.) The most expensive and deadliest severe weather outbreak of 2013 hit on May 20, when Moore, Oklahoma was devastated by an Ef-5 tornado that killed 23 people and did $2 billion in damage.

Stay Safe!
November is a highly unusual time to be getting a dangerous severe weather outbreak, but people need to take this event seriously. The four previous November "High Risk" events (1989, 1994, 2002, and 2005) have resulted in a total of 148 tornadoes and 62 fatalities (thanks go to wunderground member Neapolitan for this stat). Stay Safe!

Jeff Masters