Derecho with 100 mph winds moving throughout the Midwest

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A very dangerous derecho is moving out of Iowa into northern Illinois, toward Chicago, prompting the SPC to issue a PDS thunderstorm watch through 7 p.m. central time Monday.

“PDS severe thunderstorm watches are rare, and reserved for only the strongest thunderstorm events,” CNN meteorologist Brandon Miller said. “Wind gusts are expected to reach up 100 mph with the line of thunderstorms as rolls across northern Illinois and southern Wisconsin.”

About Derecho
A derecho (, from Spanish: derecho [deˈɾetʃo], “straight”) is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system.Derechos can cause hurricane-force winds, tornadoes, heavy rains, and flash floods. In many cases, convection-induced winds take on a bow echo (backward “C”) form of squall line, often forming beneath an area of diverging upper tropospheric winds, and in a region of both rich low-level moisture and warm-air advection. Derechos move rapidly in the direction of movement of their associated storms, similar to an outflow boundary (gust front), except that the wind remains sustained for a greater period of time (often increasing in strength after onset), and may exceed hurricane-force. A derecho-producing convective system may remain active for many hours and, occasionally, over multiple days.
A warm-weather phenomenon, derechos occur mostly in summer, especially during June, July, and August in the Northern Hemisphere, within areas of moderately strong instability and moderately strong vertical wind shear. However, derechos may occur at any time of the year, and can occur as frequently at night as during the day.
Various studies since the 1980s have shed light on the physical processes responsible for the production of widespread damaging winds by thunderstorms. In addition, it has become apparent that the most damaging derechos are associated with particular types of mesoscale convective systems that are self-perpetuating (meaning that the convective systems are not strongly dependent on the larger-scale meteorological processes such as those associated with blizzard-producing winter storms and strong cold fronts). In addition, the term “derecho” sometimes is misapplied to convectively-generated wind events that are not particularly well-organized or long-lasting. For these reasons, a more precise, physically-based definition of “derecho” has been introduced within the meteorological community.

Derecho with 100 mph winds moving across the Midwest

About moving
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A wind gust of a 106 mph in Marshall, Iowa, has already been reported as this storm passed through.

Derecho with 100 mph winds moving across the Midwest

“A derecho producing widespread damaging winds, some of which should be intense, is expected to persist and expand east from Iowa into parts of the Midwest through this evening,” the Storm Prediction Center said Monday.

A derecho (pronounced similar to “deh-REY-cho”) is a widespread, long-lived wind storm associated with a band of rapidly moving showers or thunderstorms.

A derecho can produce destruction similar to that of a tornado, but the damage typically occurs in one direction along a relatively straight swath. The term “straight-line wind damage” sometimes is used to describe derecho damage, says the SPC.

This storm complex is within the same area that is also under a moderate risk (level 4 of 5) for severe storms. The SPC upgraded this risk level Monday afternoon because of the formation of the derecho. The risk area includes over 13 million people.

In addition to wind damage, large hail — one and a half inches in diameter — is possible and a couple tornadoes possible.

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