Monday's Severe Weather: The Largest Outbreak Ever?

April 6, 2011; 12:00 PM ET
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Lightning from a fast-moving thunderstorm moves through the San Fernando Valley area of Los Angeles during the early morning of Wednesday, Dec. 27, 2006. A strong cold front was expected to move through the region Wednesday, bringing rain, snow in the mountains and strong and gusty winds, forecasters said. (AP Photo/Mike Meadows)

Destructive thunderstorms associated with a potent storm system rumbled across the eastern third of the country Monday and Monday night, producing more than 1,300 reports of damage from Texas through Pennsylvania.

Damage reports continue to flurry into the Storm Prediction Center, but the latest numbers show at least 1,377 reports of severe weather between 8 a.m. EST Monday and 8 a.m. EST Tuesday.

With such a large and unprecedented amount of severe weather reports, the question has been raised: Is this the largest single day severe weather outbreak in history? Expert Senior Meteorologist Henry Margusity said that this was the largest number of severe weather reports in a 24-hour time period that he had ever seen.

Looking a little closer at the data, there are several factors that need to be taken into consideration.

First off, in this day and age with the technology that is available, severe weather reports are much easier to receive and report.

In addition, there is the fact that these thunderstorms affected a region of the country with a rather large population. If the same severe weather outbreak occurred in the Plains where the population density is lower, there likely would have been fewer reports overall.

Another factor to consider is that the Storm Prediction Center, which takes all of the storm reports from local offices and combines it into one report, used to use certain filters on the data.

Late last year, the center removed their filters, which did not plot multiple reports of the same event if they were within 15 miles of each other. Therefore, the data this severe weather season is truly raw with every single report being plotted on the map.

In speaking with Meteorologist Greg Carbin of the Storm Prediction Center, he said that "if you add in the filters from a year ago on the preliminary data from Monday, you end up with approximately 850 severe weather reports."

Only two other events have been observed with more than 850 severe weather reports. Those events occurred on May 30, 2004 and April 2, 2006.

Carbin said, "If you take the numbers literally in terms of overall severe weather reports with the time/space filtering, April 4, 2011 would fall into third place."

He also stated, "As far as wind reports, it appears that, even with filtering, this most recent event

may have the greatest number of severe wind reports in a single 24-hour period on record."

However, Carbin mentioned that the final numbers would not be complete for several days, as reports continue to come into the Storm Prediction Center from local offices. Therefore, it is possible that this event ends up being the largest severe weather outbreak ever in terms of the number of reports.


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