The massive storm that swept through the area on Friday, June 29th, 2012, will not soon be forgotten by many folks around the northwest Ohio and northeast Indiana region. Packing winds of over 80 mph, the derecho [pronounced "day-RAY-cho"] raced through, uprooting trees, tearing off roofs, and knocking down hundreds of power-lines across the region. But it wasn't just our area that was impacted by this record-setting storm. The monster caused widespread and intense damage from northwest Indiana all the way to the East Coast, making it one of longest and most intense derechoes to ever impact the United States east of the Mississippi River. In total, the storm caused billions of dollars in damage and cut-off electricity to more than three million people.
In any given year, northwest Ohio and northeast Indiana are usually impacted by one or two derechoes in the summer. However, derechoes as violent as the one we experienced in late June 2012 are rare across the area. Derechoes, by the Storm Prediction Center definition, most produce significant wind damage [winds of 60 mph or greater] over a distance of 200 miles. However, this derecho produced winds in excess of 70 mph over a distance of over 800 miles. The Storm Prediction Center received around 900+ wind reports from the system that day. This made the event unique, rare and not likely to occur again for many years. So what factors lead up to this impressive event?
One of the major factors in the production and the sustenance of the system over a long distance was the fact that a weak, Canadian cold-front had settled across the area. North of the front, temperatures had dropped into the lower 90's, with dew points in the low-mid 60's. South of the front [the front was basically along the U.S. 30 corridor], temperatures were in the mid-upper 90's and dew points were in the low-mid 70's [Fort Wayne had reached the mid-90's with a dew point in the low-mid 70's by noon]. The incredibly hot and humid air mass present south of the front caused instability levels to sky-rocket. One of the parameters used to measure instability is known as CAPE [or Convective Available Potential Energy]; normal values of CAPE range from 1000-3000 J/kg on any given summer day. On this particular summer day, values were as high as 5000-6000 J/kg, especially in Southern Ohio. When instability levels are this high, thunderstorm formation can be explosive and deadly, which is exactly what happened.
At the same time, the intense levels of instability in the atmosphere allowed the thunderstorms to force the dry-air downward into the lower-atmosphere, which is what contributed to the very strong wind gusts that were observed at the surface. Because of the hot, humid atmosphere south of the front, the storm system was able to maintained all the way to the East Coast. This was unusual because most storm systems of this magnitude require a great deal of wind-shear throughout the atmosphere, and on this particular day, there was little or no shear.
The most damaging aspect of this storm system was the fact that it hit with little or no warning. Early in the morning on Friday, June 29, Storm Prediction Center forecasters noted that thunderstorms were possible across the area, but they were not originally expecting severe weather. They believed that the cap, a warm-layer in the mid-levels of the atmosphere, would inhibit widespread thunderstorm formation. However, by the mid-morning hours, the SPC realized that storms were already breaking through the cap and becoming organized over northeast Illinois and northwest Indiana, which lead them to include the threat of severe weather.
By this time, the thunderstorms had already organized and were racing eastward at speeds of up to 70 mph, giving little or no advanced warning time to those in the path of the storm. That is why severe thunderstorm and tornado warnings were only issued minutes in advance of the strongest wind gusts impacting areas. The local NWS did not realize that the storm system was developing so rapidly and had to race to issue warnings in advance to protect lives and property.
The problem was made worse by the fact that people were also caught off-guard. The storms were not forecasted in advance and were only able to be tracked after it had already done considerable damage. The damage it caused was further compounded, especially when hundreds of thousands of people were without power during one of the worst heat waves that has ever hit the eastern United States. The record heat and humidity contributed to several deaths after the storm was over with.
The good news is that this system isn't one that we will likely see again for several years, if not decades. The aftermath of this massive storm has caused us to realize how important it is to remain prepared and protected during forecasted severe weather events, and hopefully a re-analysis of the event by forecasters around the nation will help to improve forecasts of similar events and save lives in the future.
In any given year, northwest Ohio and northeast Indiana are usually impacted by one or two derechoes in the summer. However, derechoes as violent as the one we experienced in late June 2012 are rare across the area. Derechoes, by the Storm Prediction Center definition, most produce significant wind damage [winds of 60 mph or greater] over a distance of 200 miles. However, this derecho produced winds in excess of 70 mph over a distance of over 800 miles. The Storm Prediction Center received around 900+ wind reports from the system that day. This made the event unique, rare and not likely to occur again for many years. So what factors lead up to this impressive event?
One of the major factors in the production and the sustenance of the system over a long distance was the fact that a weak, Canadian cold-front had settled across the area. North of the front, temperatures had dropped into the lower 90's, with dew points in the low-mid 60's. South of the front [the front was basically along the U.S. 30 corridor], temperatures were in the mid-upper 90's and dew points were in the low-mid 70's [Fort Wayne had reached the mid-90's with a dew point in the low-mid 70's by noon]. The incredibly hot and humid air mass present south of the front caused instability levels to sky-rocket. One of the parameters used to measure instability is known as CAPE [or Convective Available Potential Energy]; normal values of CAPE range from 1000-3000 J/kg on any given summer day. On this particular summer day, values were as high as 5000-6000 J/kg, especially in Southern Ohio. When instability levels are this high, thunderstorm formation can be explosive and deadly, which is exactly what happened.
At the same time, the intense levels of instability in the atmosphere allowed the thunderstorms to force the dry-air downward into the lower-atmosphere, which is what contributed to the very strong wind gusts that were observed at the surface. Because of the hot, humid atmosphere south of the front, the storm system was able to maintained all the way to the East Coast. This was unusual because most storm systems of this magnitude require a great deal of wind-shear throughout the atmosphere, and on this particular day, there was little or no shear.
The most damaging aspect of this storm system was the fact that it hit with little or no warning. Early in the morning on Friday, June 29, Storm Prediction Center forecasters noted that thunderstorms were possible across the area, but they were not originally expecting severe weather. They believed that the cap, a warm-layer in the mid-levels of the atmosphere, would inhibit widespread thunderstorm formation. However, by the mid-morning hours, the SPC realized that storms were already breaking through the cap and becoming organized over northeast Illinois and northwest Indiana, which lead them to include the threat of severe weather.
By this time, the thunderstorms had already organized and were racing eastward at speeds of up to 70 mph, giving little or no advanced warning time to those in the path of the storm. That is why severe thunderstorm and tornado warnings were only issued minutes in advance of the strongest wind gusts impacting areas. The local NWS did not realize that the storm system was developing so rapidly and had to race to issue warnings in advance to protect lives and property.
The problem was made worse by the fact that people were also caught off-guard. The storms were not forecasted in advance and were only able to be tracked after it had already done considerable damage. The damage it caused was further compounded, especially when hundreds of thousands of people were without power during one of the worst heat waves that has ever hit the eastern United States. The record heat and humidity contributed to several deaths after the storm was over with.
The good news is that this system isn't one that we will likely see again for several years, if not decades. The aftermath of this massive storm has caused us to realize how important it is to remain prepared and protected during forecasted severe weather events, and hopefully a re-analysis of the event by forecasters around the nation will help to improve forecasts of similar events and save lives in the future.
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