Radar loop of the derecho as it was producing its strongest wind gusts in eastern Iowa on Monday morning. Current radar loop (NWS)

1:16 p.m. update: The storm has weakened since it entered Wisconsin and Illinois, and has now tracked as far east Kalamazoo, Mich.

[National Weather Service: Current U.S. radar loop]

A severe thunderstorm watch continues for northern Illinois and northwest Indiana until 3 p.m. central time. Damaging wind reports are mostly confined to northern Iowa and southwest Wisconsin when the derecho appears to have been at its peak intensity:

This radar loop starting around 6 a.m. central time shows how the main mesoscale convective system tracked across southern Minnesota and northern Iowa, and eventually spawned the windy derecho.


Radar imagery of the mesoscale convective complex that spawned the derecho. The loop starts around 6 a.m. eastern time, and ends at 1 p.m. (Weather Underground)

12:10 p.m. update: Photos of damage in eastern Iowa are appearing on social media, including this from the area around Oelwein and Fayette, via KGAN-TV.  Weather stations are sparse in this area, but the region is just north of Independence, Iowa, which recorded a gust around 90 mph on Monday morning.

The straight-line winds flattened this corn field in Floyd County, Iowa. The photographer says that the stalks just appear to be bent and not broken, though he hasn’t really surveyed the damage yet.

Original post:

A damaging derecho is blasting across the Midwest on Monday, with the ability to produce gusts in excess of 80 mph, hail large than two inches in diameter and isolated tornadoes.

Severe thunderstorm watches are in effect for east-central Iowa, southern Wisconsin and northern Illinois, including the Chicagoland area as the storm tracks east.  Derechos are long-lived, damaging wind storms that have the ability to inflict damage that’s similar to a tornado, though is technically the result of straight-line winds.

[Everything you need to know about derechos]

If the derecho lasts through the early afternoon, it will likely track across the Upper Midwest, and not sink south into the D.C. area a la 2012. Radar imagery indicates the storm is weakening as it traverses Wisconsin and Illinois, so it’s possible that Chicago and points east will be spared the storm’s strongest wind gusts.


Severe thunderstorm watch (pink). (NWS)

According to reporting by weather.com, notable wind gusts so far include:

Sheldon, Iowa — 95 mph
Independence, Iowa — 93 mph
Dubuque, Iowa — 80 mph
De Smet, S.D. — 81 mph
Sioux Falls, S.D. — 72 mph

The storm took shape from what meteorologists call a mesoscale convective system that formed in the northern Plains late on Sunday night. As the sun came up over the Midwest, the system exploded over southern Minnesota and northern Iowa, and by 8 a.m., the southern flank of the system had developed the classic bow echo shape, indicative of damaging wind gusts.

[National Weather Service: Current U.S. radar loop]

Some flights in and out of the Chicago area have been canceled already — O’Hare International suggests checking your flight status with the airline before you leave.

The Weather Channel’s Jon Erdman shared this image of the wind damage reports that stretches back to western South Dakota in the early morning hours as the convective system was just starting to form. Since then it’s tracked over 700 miles into southern Wisconsin and northern Illinois.

The storm has had a history of producing damaging winds, particularly in eastern Iowa where a 95 mph gust was recorded and a plane hangar was destroyed.