Pile-up

I was in the news. Big ‘ol car pile up on the Bong Bridge due to fog occurred back on Thursday. I was interviewed about the weather conditions surrounding the incident. I will let the article do the rest of the talking…



NO VISIBILITY: Rare conditions turn fog into driving peril


NEWS TRIBUNE STAFF WRITER

Several unique weather conditions combined Thursday morning to create a freak fog bank that hovered over the Bong Bridge and contributed to a multicar pileup.

National Weather Service forecasters stationed near Duluth International Airport, atop the hill, didn’t see the fog along St. Louis Bay. But based on history, they explained what may have caused the problem.

First, a fairly common fog developed over the open waters of Lake Superior, said meteorologist Kurt Mayer of the weather service’s Duluth office. Very cold air blows over the moist air rising up from the warmer water, creating a steamy layer of fog that usually hangs over the lake.

On Thursday morning, some of that fog slowly moved over the frozen harbor and parts of Duluth and Superior, creating a stunning landscape view for commuters.

Mayer said a strong high pressure system over the Northland, coupled with very light winds, caused an air inversion to trap air near the surface and keep it from dispersing or mixing, as usually happens early each day.

As the sun rose, the layer closest to the ground warmed slightly, forcing out the foggy, cooler air at that level. But the air inversion kept the fog from completely dispersing.

Another band of fog appeared to hang about 100 feet above the surface — just at the height of the bridge deck. People at the accident scene said entrances to the bridge were completely clear. Only when they approached the highest, center span of the bridge did they hit a solid wall of fog.

By mid-morning, the fog had lifted from the bridge.

“What seems to have happened is that a layer of fog got trapped between warmer air above and below. It’s not all that unusual. But it’s a fairly unique situation to see it last very long,” Mayer said.

A similar situation happened on June 30, 1992, when a derailed train car, south of Superior, leaked benzene gas. An air inversion and light winds held the gas cloud close the ground, prompting evacuations of much of Duluth and Superior. Only when the inversion lifted and winds increased did the gas cloud completely disperse.

Air inversions often cause smoke, steam and exhaust to hang low in the air, creating hazy conditions and, occasionally, spurring air-quality warnings. Additionally, the Twin Ports’ unique geography, with hills trapping air below, contributes to the stagnated air conditions.

…and here is a more comprehensive article that gives a thorough background…



Fog blamed in fatal pileup
16-VEHICLE CRASH: A newborn baby died and seven were hurt Thursday morning.

NEWS TRIBUNE STAFF WRITERS