AccuWeather forecasters warn of derecho risk in central US
AccuWeather meteorologists are monitoring the potential for a high-powered, long-tracking and fast-moving batch of thunderstorms, known as a derecho, to develop during the balance of this week across parts of the central United States. One such derecho may be evolving over part of the Ohio Valley on Thursday afternoon.
In simple terms, a derecho behaves like an inland hurricane with a large batch of damaging winds and heavy rainfall that can at times lead to significant flooding.
The National Weather Service has developed criteria to distinguish derechos from other less intense and shorter-distance thunderstorm complexes. In order for a derecho to be declared, usually via a post-storm analysis, the storms must have traveled 400 miles or more with a width of at least 60 miles. The storms also must have produced damage nearly continuously along that path.
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However, there will still be a significant risk to lives and property from a complex of severe thunderstorms this week - whether a derecho is officially declared or not.
"Complexes of thunderstorms will erupt near and north of the rim of tremendous heat, which is anchored over Texas and the southern Plains this week," AccuWeather Senior Meteorologist Dan Pydynowski said. "One day and night in particular - Thursday - may represent a higher risk for one or more derechos."
There are two zones where a derecho may evolve from clusters of severe thunderstorms, AccuWeather forecasters say.
Thunderstorms will continue to erupt and try to organize into complexes in portions of Illinois, southern Michigan, Indiana, western Ohio, Kentucky and Tennessee.
One such complex produced a lot of lightning strikes in southern portions of Illinois and Indiana to central and western Kentucky into Thursday midday.
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Because there are multiple areas where thunderstorms could merge into dangerous and far-reaching complexes, it is possible that some places could be hit by two rounds of dangerous thunderstorms in 12 hours.
Another complex of storms that fired up in parts of Kansas, Nebraska, Iowa and Missouri from Wednesday night was rolling to the east on Thursday afternoon parts of Illinois, Indiana and Kentucky once again. A turn toward the southeast is likely Thursday night.
Not only will there be a high level threat from high winds and hail, but also for flash flooding despite any existing drought conditions.
Just as all thunderstorms are not created equal, the same is true for derechos.
On Aug. 10, 2020, an intense derecho produced a swath of high winds and leveled crops from eastern Nebraska to parts of Michigan and northern and central Indiana. The damage swath extended for nearly 800 miles with a peak wind gust of 126 mph recorded in Atkins, Iowa.
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The derecho raced eastward across the Midwest, causing destruction along its path on Monday, Aug. 10, 2020. (NWS Chicago) |
That derecho resulted in at least four fatalities and more than $11 billion in damages across the Midwest.
On June 29, 2012, one of the most powerful derechos in recent memory caused substantial damage to the Washington, D.C., area. The storm produced significant wind damage along an 800-mile path from Iowa to the Delmarva Peninsula.
The zone from the eastern slopes of the central Rockies through the central Plains will be another hot spot for thunderstorm complexes and perhaps a derecho.
"Parts of Nebraska, northern Kansas, northwestern Missouri and southwestern Iowa was one area hit by a complex of severe thunderstorms on Thursday morning," Pydynowski said. The storms produced strong winds, hail, torrential downpours and perhaps flash flooding.
Some severe storms may erupt farther to the west in portions of Colorado and Wyoming as well. This could evolve into the second long-lasting complex for Thursday night.
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From this zone, should an intense complex of storms evolve, it may continue to roll through the late-night hours Thursday and then across the middle portion of the Mississippi Valley and then perhaps into portions of the Ohio or Tennessee valleys Friday.
Predicting the precise path complexes will take is extremely challenging, especially more than 24 hours in advance with storms that have not formed yet.
"The exact initial eruption of thunderstorms on Thursday and their intensity will determine how long they may survive and which areas may be hit or missed by the complex hundreds of miles away a day later," AccuWeather Senior Meteorologist Brett Anderson said. It is possible a long-lived complex such as a derecho could reach as far as parts of the southern and central Appalachians.
Similarly, a complex that erupts on the eastern Plains of Colorado Thursday evening could roll hundreds of miles to the east during Thursday night and early Friday to across the Mississippi Valley.
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By the extended Independence Day weekend, the heat dome over the South Central states will break down and the risk of a derecho may decrease.
However, as weather systems continue to move along from west to east across the nation, there will still be episodes of thunderstorms, including large complexes of damaging and dangerous severe weather, in the central region through July 4, just as millions seek the outdoors for holiday activities.
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