National Weather Service United States Department of Commerce

Significant Severe Weather Outbreak Likely Today

A significant severe thunderstorm outbreak is likely for portions of the Midwest this afternoon and evening, especially from eastern Iowa into northern and central Illinois. The threats include tornadoes, a few which may be significant, large to very large hail, and damaging winds. A powerful system near the Central Plains will lift north and clash with a warm and humid air mass over the region. Read More >

Slide 23

'Non-Weather Issues'

Slides 1 through 15 of this presentation addressed the aspects of the ‘overpass’ issues in relation to tornadoes. Slides 16 through 19 have addressed the other meteorological aspects associated with severe thunderstorms. However, we have not yet directly addressed the non-meteorological reasons why this practice must be minimized. We will do that here.

Other extremely important reasons why seeking shelter from tornadoes and severe storms underneath overpasses are the non-weather issues. This has been alluded to in several of the previous slides, most notably the ones describing the happenings at the Shields Boulevard overpass (Slide 8 and Slide 9) on May 3, and will be explained here.

When a traffic jam results from blocked free flow of traffic because a multitude of vehicles parked near an overpass, this forces many others into the same desperate situation, unnecessarily. This happened at Shields Boulevard on May 3, and has also happened in several other severe storm situations. Once people start to seek shelter under overpasses, a potentially lethal series of consequences begins. First, the free flow of traffic is blocked. Then other potential escape routes are blocked by this stalled traffic, especially on limited-access roads such as interstate highways. There is also the potential for a major traffic accident in the form of a chain reaction during low visibility and/or nighttime events, where oncoming traffic might not be able to see the stopped vehicles in time to prevent collisions, adding to the blockage. A tornado hitting such an involuntary assemblage of vehicles will leave a deposit of rubble and vehicles, rendering the road impassible for several hours. The blocked road would prevent emergency vehicles from gaining access to the affected areas; this did happen on May 3rd in the Oklahoma City metro area. Despite all of the incredibly valid meteorological reasons why overpasses are very bad places to be, the traffic blockage aspect may be just as important of a reason why we need to minimize this practice! WE MUST AVOID FORCING OTHERS INTO THE SAME DESPERATE SITUATION BY BLOCKING THE ROAD!

Finally, there were also a few people on May 3 who ACTUALLY LEFT THEIR HOMES TO DRIVE TO THE NEAREST HIGHWAY OVERPASS TO SEEK SHELTER! As has been stated before in Slide 21, the current guidelines for people in buildings are EXTREMELY effective when practiced properly, and in almost no instance should one leave a soundly constructed building that has an interior room in a tornado situation!

Yet further evidence of how far the myth of overpasses offering good shelter from tornadoes was provided by one of the co-authors of this paper. He told a story of one of his friends who moved to a new apartment building shortly after the May 3 event. One of the first things his friend did after moving to the new apartment complex was to go for a drive and scope out the ‘best’ overpass to go to in the event of another tornado! It SHOULD be noted that this person DID do one thing correctly – THEY MADE A PLAN. However, it is one of our goals as meteorologists to make sure that we help people plan PROPERLY for severe weather events by providing the best possible practical advice and safety guidelines!

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