"Was that a derecho?"
It's a popular term in meteorology for a storm event. But not every bad storm that passes through is a derecho. There are actually distinct characteristics that classify a weather event as a derecho.
A derecho is a widespread, long-lived wind storm associated with a band of rapidly moving showers or thunderstorms.
The destruction is similar to tornadoes, but the damage is usually directed in one direction.
Two characteristics it must have include:
- The wind damage swath extends more than 240 miles
- Wind gusts have to reach at least 58 mph along most of its length
A derecho can bring hurricane-force winds and cause serious impacts. Impacts include damage to crops and property. Downed trees can damage cars and building, and downed power poles can lead to power outages.
In extreme cases, these winds can lead to the loss of life.
As a rain-cooled downdraft of a thunderstorm reaches the surface, it spreads horizontally and forces the warm, moist air surrounding the storm up along the leading edge of the outflow.
Once the warm, moist air travels upwards, new storms form. The rain from these storms reinforces the cold pool, strengthening the flow of air from the backside of the storm and encouraging the downward transport of stronger winds from the top of the storms.
As the thunderstorms increase in coverage, more rain-cooled air reinforces the cold pool. The line of storms accelerates as one large bow or multiple smaller bows within an overall line. During this event, persistent wind damage occurs.
Predicting a derecho in advance is very difficult. The characteristics are very specific, and the processes that lead to a derecho are small-scale.
It’s easier to identify a derecho when the storms are happening, which in the end, could only give a few hours’ notice.
It is much easier to predict where severe weather might be possible. If the National Weather Service forecasts severe weather for your area, it is best to prepare before the event. This way, you’ll be ready for whatever happens.