Thursday, November 21, 2013

Summary of Sunday's Tornado Outbreak

We will never know how many lives were saved or injuries avoided because of the timely and accurate warnings issued during Sunday's severe weather outbreak. It's easier to speculate on what could have been had there not been enough advance for people to take cover, and that picture isn't pretty.

The science of meteorology and the art and science of forecasting have come a long way in the last two decades. Technology has advanced, the forecasts are much better, there has been a greater effort at public education, and there are now multiple avenues to disseminate this information, including social media. Nevertheless, it takes the skill of the forecasters, the cooperation of the media, and the efforts of volunteer storm spotters for the system to work.  It certainly worked well on Sunday, November 17.  More importantly, those in the storm's path heeded warnings and took shelter.

The Storm Prediction Center had indicated the possibility of severe weather on Sunday as early as Thursday. As the forecast became clearer the outlook issued Saturday indicated a Moderate Risk for severe storms on Sunday.

The outlook issued early Sunday morning upgraded that to a High Risk for portions of Illinois and Indiana. SPC expanded that High Risk area in the next update issued at 8:00 a.m. CST through Indiana and into Ohio. High Risk outlooks for severe weather are pretty rare in November.

The SPC forecasters are very skilled at what they do, but often Mother Nature throws curveballs and forecasts aren't always perfect. On Sunday, however, they hit a home run out of the park (to maintain the baseball analogy). Here is map of all the storm reports received superimposed on the outlook map issued Sunday morning. Note that all but a few tornadoes occurred in the High Risk area, and all reports fell within the area outlined by the Slight Risk (yellow) - most were within the Moderate Risk area..

To go along with the above map, here is a summary map of all the watches and warnings issued between Saturday morning and Monday morning.

What made this day particularly challenging was the forward speed of the supercells and thunderstorms. Many were moving at 60 to 65 mph, so a delay in issuing a warning even for five minutes meant that a storm was five miles closer to a particular location.  Fortunately advances in radar technology allow forecasters to detect tornado potential before a tornado actually forms providing more lead time for a warning. Residents in Washington, IL were warned 15 minutes before the monster hit, no doubt a reason that more people weren't killed or injured.

Here is a summary of the strongest tornadoes that occurred on Sunday. There were a total of 24 tornadoes in Illinois and 24 in Indiana (preliminary numbers). Tornadoes also occurred in Kentucky, Missouri, Michigan, Ohio, and Tennessee. Seven tornadoes have been rated EF-3 and two have been rated EF-4 on the Enhanced Fujita Scale.  Of those nine EF3/EF4 tornadoes two tornadoes, including the EF-4 that hit Washington, Illinois, traveled over 40 miles and two others traveled more than 29 miles.

Tornado Est. Path Max
Location Intensity Max Wind  Length Width
Washington, IL (Tazewell/Woodford County) EF4 190 46.2 1/2 mile
New Minden, IL (Washington County) EF4 166 10.6 200 yds
Gifford, IL (Champaign/Vermilion) EF3 140 29.7 1/4 mile
Villa Grove (Douglas and Champaign) EF3 140 15.0 1/4 mile
Lafayette, IN EF3 NA 29.2 NA
Woodville, KY EF3 145 42.0 500 yds
Hopkins County, KY EF3 140 8.0 200 yds
Union/Henderson County. IL EF3 145 14.5 200 yds
Scott County, MO EF3 140 19.0 600 yds

Most of the damage surveys are complete, but the data presented here is still preliminary and subject to change as more storm reports come in. NWS offices are still updating information on their web pages. The NWS Chicago office and NWS Lincoln, IL office both have extensive information, maps, videos, and photographs on their web sites, as well as links to the other NWS offices with storm information on this outbreak.

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