Posted by: JeffMasters, 2:45 PM GMT on April 18, 2011

In a stunning display of violence, close to 200 tornadoes rampaged across the Midwestern and Southeast U.S. April 14 - 16 in one of the largest tornado outbreaks in history. At least 40 people died in the tornadoes, making it the deadliest tornado outbreak since the Super Tuesday tornado outbreak of February 5 - 6, 2008, which killed 57 people. Severe thunderstorms and flash floods killed at least seven more people in this April's severe weather outbreak. Hardest hit was Bertie Country in northeast North Carolina, where an EF-3 tornado carved a path of destruction 18.8 miles long and 1/2 - 3/4 miles wide, killing 11 people in the town of Colerain. It was the deadliest single tornado in the United States since May 10, 2008 in Picher, Oklahoma and Neosho, Missouri, which killed 21. Also hard-hit Saturday was the Raleigh area, where a 3/10 mile-wide tornado carved a 63-mile long path of destruction through downtown. Damage was rated EF-2 in downtown Raleigh, but was EF-3 along other portions of its path, and the tornado killed five people. The 23 tornado deaths in North Carolina made Saturday's outbreak the deadliest day for tornadoes in the state since 1984, when the infamous March 28 tornado outbreak killed 57 people and injured 1248. The 1984 outbreak had more violent tornadoes--seven F4 twisters in all. None of the tornadoes in this year's outbreak have been rated above EF-3, as of yet.


Figure 1. Viewer-uploaded photo sent to WRAL of damage in Fayetteville, NC on Saturday.


Figure 2. Radar reflectivity image of North Carolina on Saturday during the height of the tornado outbreak, showing four simultaneous hook echoes of tornadoes. The storm at the top of the image is the EF-3 tornado that ripped through Raleigh, killing five people.

One of the largest tornado outbreaks in history
NOAA's Storm Prediction Center logged 120 preliminary tornado reports on Saturday, 120 on Friday, and 27 on Thursday, bringing the 3-day total to 267 twisters. In past years, these preliminary tornado reports typically were an over-count of the actual confirmed tornado totals by about 15%. However, this year the Storm Prediction Center stopped trying to filter out preliminary reports they thought were from the same tornado, so the over-count may be higher. Even so, the 3-day April 14 - 16 2011 tornado outbreak will likely will end up with close to 200 confirmed tornadoes, making it the largest tornado outbreak since the 235 tornadoes recorded in the May 22 - 31, 2008 outbreak. According to a list of tornado outbreaks maintained by Wikipedia, only two other tornado outbreaks have had as many as 150 twisters--the May 2004 outbreak (385), and the May 2003 outbreak (401). An average April typically has 150 - 160 tornadoes across the entire U.S.


Figure 3. Steven Hoag sat in his car filming the EF-2 tornado that hit Wilson, North Carolina on Saturday. We can hear his side of a cell phone conversation as the tornado passes directly over him, unroofing a Walgreens store across the street. His calmness and lack of concern are truly extraordinary to hear. Hoag was very fortunate, as the 120-mph winds of the tornado rolled several cars as much as 100 feet.

Another significant severe weather outbreak coming on Tuesday
NOAA's Storm Prediction Center is predicting another major severe weather outbreak for the Midwest on Tuesday, when a strong cold front is expected to sweep across the Mississippi and Ohio River Valleys. A "moderate" risk of severe weather is expected across much of Missouri, Illinois, and Indiana. The weather conditions are not expected to be as conducive for severe weather as was the case Saturday, when SPC placed much of North Carolina in their "high risk" area for severe weather, the only "high risk" forecast they've issued this year.


Figure 4. Severe weather risk for Tuesday.

Wikipedia has a nice summary of the April 14 - 16 tornado outbreak.

Jeff Masters