Derechos- Straight line winds

Spanish for “straight,” a derecho is a wide, straight-¬line wind storm with speeds over 58 mph that generates a continuous series of severe thunderstorms. Wind speeds in a derecho typically increase after the passing of its associated front and approach 100 mph. The strongest recorded have peaked around 130 mph. Low¬-level warm air advection, rich low-¬level moisture and wind divergence in the upper troposphere are necessary for the formation of derechos. Their bow or spear¬headed appearance on radar has lent them their nicknames “bow” and “spearhead” echoes. If a derecho converges to less than 2.5 miles across, it becomes a microburst. Beyond the threats associated with all thunderstorms, derechos likely cause flash flooding and often spawn tornadoes. Although they may occur at any time of the year, day or night, they’re most common in the Northern Hemisphere during the summer.

A strong downburst from a derecho is inescapable for most aircraft and significantly adds to the force of gravity, which makes crash landings more violent. A sky with small pockets of storms may seem penetrable but, if meteorologists predict the imminent formation of a derecho, aircraft must avoid it because hazardous winds are present and new storms are developing.
Photo below NOAA.

Written by
Meteorologist Geoff Linsley