After what has already been a very active tornado season for the US, meteorologists are now warning of the possibility of severe windstorms hitting some parts over the next few days. This next round of bad weather is due to a feature known as a derecho.
The word derecho literally means ‘straight’ in Spanish. The weather phenomenon is defined as a widespread and long-lived windstorm that accompanies rapidly moving showers and thunderstorms. They can trigger tornadoes, lightning and large hail storms.
The storms are expected to form across South Dakota to Pennsylvania. Cities at risk include Milwaukee, Chicago, Cleveland, Indianapolis, Cincinnati, Detroit, Baltimore, Washington, Pittsburgh and Louisville.
Derechos typically strike the lower Midwest states once every year, but are relatively rare across the Mid-Atlantic States. On average, this region is affected by them once every four years.
To be classed as a derecho, a storm must cause damage over 400 kilometers and contain gusts of wind at least 93 kph. Last year on June 29 a small group of thunderstorms developed in the Chicago area.
The storm steadily rumbled eastwards. As they did so, they gathered power and momentum, reaching a peak over Virginia and Washington DC, around 1000 km away. Winds gusting as high as 145 kph were recorded.
The damaged caused by the storm was estimated to be on par with an EF-1 tornadom but over a much larger area. There was a trail of destruction over 1000 km long across the Midwest and Mid-Atlantic, cutting power to four million residents and killing 13 people.