Thunderstorm Outflow Likely Caused Last Night’s Electrical Trouble, Rolling Green Country Club Trouble Today


The edge of the outflow boundary (the thin bowing gray line moving south from the yellow and red thunderstorm complex) was detected by Doppler radar and traveled through Arlington Heights and Mount Prospect just before 9:50 p.m. Wednesday. [See LIVE CHICAGO RADAR]

‘Outflow’ — the National Weather Service warned about it hours before they issued a Severe Thunderstorm Warning about 11:00 p.m. for our northern Cook County. Severe storms were already pounding southeast Wisconsin when an outflow of rain-cooled air radiated north to south from the main storm, which was traveling west to east in Wisconsin. The outflow boundary marks the border of the cool downdraft from thunderstorms, distinctly from the warmer air that residents experienced all day.

Outflow boundaries are interesting because sometimes new storms develop in the boundary, but sometimes the boundary cuts off the supply of warm, humid air that feeds the main thunderstorms, which causes the large thunderstorms to collapse and dissipate.

A severe local outflow of air from thunderstorm downdrafts is involved with microbursts, which can cause severe local damage, like a tornado, but its physically the opposite of a tornado –regarding air flow.

The outflow boundary was clearly visible on weather radar. The National Weather Service even described its path from Highland Park south in the hours ahead of the thunderstorms that hit about 11 p.m. The outflow boundary blew down large tree branches in Arlington Heights and Mount Prospect about 9:45 p.m. Wednesday. Some of the large branches took down two primary electric lines behind the Walmart on Rand Road in Mount Prospect. Lines were still energized on the ground, causing arcing and surges in a few residences. A few neighbors reported that their lights in the residences were extra bright and that they heard humming near outlets and behind the wall inside their rooms.

A large branch fell and blocked Arlington Heights Road between Euclid Avenue and Oakton Street, and a large branch fell near Arthur and Davis. A tree also fell on Oakton near Gibbons Avenue.

Firefighters and Com Ed workers check on a vault and building safety at Rolling Green Country Club in Arlington Heights. Also scenes from Rand Road electric lines and a downed tree on Oakton at near Gibbons Avenue.

Electrical problems continued on Thursday. Com Ed was working on power lines and large transformers on Rand Road, just east of Camp McDonald Road, when arcing and possibly a fire started in an underground vault near the main entrance of the Rolling Green Country Club building. Firefighters, concerned that the fire or arcing could extend into the building, inspected the building with a thermal imaging camera, and requested that Com Ed workers nearby, rush over to inspect the vault. The Com Ed workers de-energized the power to the vault. Firefighters cleared a light haze that collected on the first floor near the underground vault. No fire was detected in the building. Com Ed and Asplundh Tree Expert Co. were working past 8:00 p.m. Thursday in the area.

Staff at the Rolling Green Country Club worked hard to keep disruption of a scheduled luncheon to a minimum.

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