A tornado while driving, an overpass, hail, straight-line wind and water over a road. What the NWS actually says, including where it declines to give you one answer.

In this lesson you will

  • State current NWS guidance for a tornado encountered while driving.
  • Explain why an overpass is dangerous, using the 3 May 1999 record.
  • Apply hail and straight-line wind vehicle tactics.
  • Apply Turn Around Don't Drown with the correct water depths.

A tornado, while driving

The NWS guidance, quoted exactly, because this is the one place in the course where paraphrase would be dangerous:

In a vehicle: Being in a vehicle during a tornado is not safe. The
best course of action is to drive to the closest shelter. If you are
unable to make it to a safe shelter, either get down in your car and
cover your head, or abandon your car and seek shelter in a low lying
area such as a ditch or ravine.

NWS, what to do during a tornado, read 11 September 2026. Quoted in full.

Read the word "either"
The NWS gives two options and does not rank them, and that is not sloppiness. Which is better genuinely depends on what is around you: whether there is a real depression lower than the roadway, whether it is about to fill with water, whether there are trees and power lines over it, how much time you have. This course is not going to publish a decision tree the agency declined to write. Know both options and know that the choice is yours in the moment.
  • If the tornado is distant and you can tell which way it is going, drive away from it at right angles to its path rather than trying to outrun it along the path.
  • The first sentence is the important one: a vehicle is not safe. Everything after it is a choice between worse options, so the whole of this module is about not arriving here.
  • A sturdy building beats both options, every time, if you can reach one.
Two things not to do
Do not open your windows to equalise pressure. It does not help, it has never helped, the pressure drop is not what destroys buildings, and it costs you seconds you need. Do not assume you can outrun it. El Reno accelerated past 50 mph and turned left, on roads with other people on them.

Overpasses

The most dangerous single piece of folklore in spotting, and it has a documented body count.

NWS Norman and NSSL, on the 3 May 1999 Oklahoma and Kansas outbreak: "highway overpasses offer, at best, questionable shelter not only from tornadoes, but severe storms in general: three people in Oklahoma lost their lives while seeking shelter near or under overpass bridges."

A cross-section through a highway overpass with wind arrows approaching from the left. The arrows crowd together and speed up as they pass through the gap under the bridge deck, drawn longer and closer on the far side. Debris is shown being funnelled into the same gap. Below, a plan view shows vehicles stopped on the carriageway at the overpass, blocking both lanes behind them.
Three separate mechanisms, any one of which would be enough: the wind accelerates through the constriction, the debris is funnelled into the same place, and the stopped vehicles trap everybody behind them. WxAlerts, after NWS Norman
  • The wind accelerates. Squeezing a flow through a smaller gap speeds it up. You have gone to the one place nearby where the wind is faster than it is in the open.
  • The debris comes with it. Whatever the wind is carrying is funnelled into the same constriction, at the same increased speed, at the height where people climb.
  • The road blocks. Vehicles stop on the carriageway and nobody behind them can move, including people who had a plan and including emergency services.
  • There is often nothing to hold. Many overpasses have no girder recess at all, just a flat underside and a sloped embankment.
Where the myth came from
Chiefly one widely distributed video from 26 April 1991 in southern Kansas, in which a television crew sheltered under an overpass and survived, plus an incident at Wichita Falls in 1979. What the video does not show is that the tornado was weak and did not directly hit the overpass. Millions of people drew a conclusion from a case that did not test it. Eight years later, three people died.

Hail

  • Face the vehicle into the hail. The windshield is the strongest and most shatter-resistant glass on the car; the side and rear glass are not. Pointing into the storm puts the strong glass where the impacts are.
  • Get occupants low and covered, away from the side windows, with a blanket or coat over heads if you have one.
  • Do not get out. Module 5 covered what large hail does at terminal velocity, and none of it is survivable well outside a vehicle.
  • Do not shelter under an overpass or a bridge to escape hail either, for every reason in the section above plus the blocked-road one.

Straight-line wind

Bow echo and downburst winds of 70 to 100 mph are a real threat to a stationary vehicle, and much more so to a high-profile one. NWS guidance is to point the vehicle directly toward or directly away from the wind, so that its aerodynamics work with you rather than presenting a broadside.

Then look at what is around you, because in most of the country the wind is not what hits you. Trees and power lines are. A position under mature trees or beside a line of poles is a bad position in a wind event even if the wind itself would not have moved you.

Water over a road

Module 6 is the hazard science and module 6 lesson 4 is why this kills more people than the rest of this module combined. Here it is a driving decision, and it is the simplest one in the course.

Depth of moving waterWhat it does
6 inchesReaches the bottom of most cars. Loss of control, possible stalling. Knocks over an adult on foot.
12 inchesFloats and carries away most cars.
2 feetCarries away most vehicles, including SUVs and pickups.

These are the NWS figures and they describe moving water. The road surface underneath may also be gone, which no depth rule covers.

Turn Around Don't Drown
Never drive into water over a road. Not ever, not in anything. You cannot see the depth, you cannot see whether the roadbed is still there, and at night you cannot see the water. This is the one place in this module where there is no judgment call and no circumstance-dependent option. Turn around.

Check yourself

A tornado is approaching, you cannot reach a building, and there is an overpass 200 yards ahead. What do you do?

  1. Do not use the overpass. Apply the NWS vehicle guidance: get down in the car and cover your head, or get to a low-lying area if one is genuinely available
  2. Shelter under the overpass and climb as high into the structure as possible
  3. Park under the overpass but stay in the vehicle with the engine running
  4. Drive under the overpass and continue through, using it for cover as you pass
Hint

One structure in this question has a documented death toll from exactly this decision.

Answer

Do not use the overpass. Apply the NWS vehicle guidance: get down in the car and cover your head, or get to a low-lying area if one is genuinely available

An overpass accelerates the wind, funnels debris into the same gap, and blocks the road for everybody behind you. Three people died doing this on 3 May 1999. The NWS gives two options for a tornado in a vehicle and neither of them is an overpass.

Sources

  1. NWS, what to do during a tornado
  2. Miller, Doswell, Brooks, Stumpf & Rasmussen, NWS Norman and NSSL: highway overpasses as tornado shelters, fallout from the 3 May 1999 Oklahoma and Kansas violent tornado outbreak
  3. NWS, Turn Around Don't Drown
  4. NWS Weather Spotter's Field Guide (YPA-201154, June 2011)
  5. NWS, severe weather safety: hail and wind