[ Freelance Traveller Home Page | Search Freelance Traveller | Site Index ]

*Freelance Traveller

The Electronic Fan-Supported Traveller® Resource

Hazard: Tornado!

This article originally appeared in the June 2015 issue.

A particularly loud thunderclap drew Willem’s gaze upward. Were he a Primitive, like his partner who’d disappeared into the underbrush to circle around their quarry, he’d say the gods were angry. The sky certainly was. Overhead, the clouds boiled black. Off to the west, they took on a greenish cast. The rain came down in sheets. The wind gusted to worrisome levels. And the lightning…it wouldn’t do to stay exposed like this.

We should wait this out in the ATV, he thought. Then he remembered how he and Bereld had chased their bounty across the subsector. They weren’t about to let him—and the 25,000 credits on his head—get away. They’d never been this close to catching him.

Cursing, Willem returned to the hunt. Staying low to avoid being struck, he tried to catch a glimpse of the other men through a face full of rain. He knew the barbarian would flush their prey toward Willem’s waiting shotgun. He had to be ready.

The rain suddenly stopped, as though Bereld’s gods had decided enough was enough and flipped the “off” switch. It was then that Willem heard it: a loud rushing sound. A waterfall, or…?

He peered westward, toward the sound. A few kilometers away, a grayish-white finger of cloud had begun a journey to the ground below. Rope-thin at first, it gained girth as it touched down and announced its presence with a roar of wind and a veil of black dust.

Willem had heard of these things, but had never seen one; now one was bearing down on him. As he cast quickly about for shelter, his mind—probably in a ludicrous attempt to keep his fear at bay—dwelled on the name for the phenomenon. The Vilani called it iirupiim. He’d heard a Vargr once call it zoghfaeng. He remembered the ancient Terran word as he dove for a welcome depression in the ground:


The worlds of the Imperium are unique, with their own beauties and their own dangers. Weather is often one of those dangers, as any planet with a thick enough atmosphere and an energetic enough star has significant meteorological events. Storm form and sometimes become life-threatening. One of those threats is an example of the worst a world’s weather has to offer: the tornado. This article builds upon “Hazard: Storm!” appearing in an earlier issue of Freelance Traveller, providing background material, scientific explanation, and a game mechanic the referee can use to implement such a disturbance.

Author’s Note: while based on real-world meteorological science, the concepts presented here are part of a game. Nothing written here is intended to be used in real-life situations. Tornadoes are dangerous weather phenomena that cause great damage and injuries. Warnings regarding their appearance should be promptly observed and authorities’ instructions strictly followed. Readers are directed to their respective national weather organizations or meteorological research institutes for more information.

Defining a Tornado

A tornado is “a rotating column of air, in contact with the surface, [suspended] from a [vertically-developed] cloud, and often visible as a funnel cloud and/or circulating debris/dust at the ground.” (American Meteorological Society.) Also called twisters, whirlwinds, or cyclones, a tornado is the most violent and unpredictable known atmospheric disturbance. Tornadoes are also among the most recognizable. They appear in many shapes and sizes, not necessarily the classic “funnel” shape. Width ranges from a few hundred meters to almost five kilometers. Winds in the most powerful examples can approach 500kph, more than enough to level almost any structure and hurl vehicles like toys. Their lifespan is typically less than ten minutes, although some last mere seconds and others can ravage the landscape for over an hour. In short, there is no such thing as the “typical” tornado.

Tornadoes are rated by a scale known as the Enhanced Fujita, or EF, scale. This scale doesn’t measure tornadic winds directly; rather it estimates the prior wind speed using a combination of observed damage and knowledge of building strengths. The scale ranges from EF0 (a weak tornado doing little damage) to EF5 (the deadliest, most powerful storms.)

A waterspout is a common tornado variant; it’s essentially a tornado over a large body of water. Generally weaker than a classic tornado, it can become one if it comes ashore. Waterspouts pose a threat to small watercraft, although larger watercraft and some aircraft have been known to survive encounters with them.

The Making of a Tornado

Tornadogenesis is complex, and a full discussion of it is beyond this article’s scope. For gaming purposes, however, a grossly oversimplified version of the events will do:

Each tornado is a unique creation, but they all start the same way: cool, dry air clashes with warm, moist air. Thunderstorms develop along the boundary between the air masses. Some of these storms develop powerful updrafts and downdrafts; the interplay of this wind shear eventually becomes rotation—a mesocyclone—within the thunderstorm. The storm then becomes a supercell. The mesocyclone in due course extends downward, pulled by intense downdrafts, through the cloud base. The visual manifestation of this is a wall cloud, and is a near-certain confirmation of impending tornadic activity. The funnel cloud extends downward out of the wall cloud, but isn’t considered a tornado until it touches the ground. The funnel may not be visible if there isn’t enough condensation to make it so; it’s thus invisible and only detectable on electronic sensors or by observing swirling debris under the wall cloud. Heavy rains and darkness may also hide an approaching tornado.

Fortunately, twisters tend to be self-limiting. The updrafts which pull in the warm air feeding the storm also draws cooler air that eventually cuts it off. The tornado soon weakens until it enters a rope-out, or a stage where it narrows until it resembles a rope or cord hanging in the sky. It dissipates soon after. However, a powerful enough parent storm can form another mesocyclone and begin the cycle again.

Particularly powerful supercells may also spawn multiple vortices, in the form of separate twin tornadoes; a smaller “satellite” tornado orbiting a much larger and stronger funnel; or multiple suction vortices revolving around a common point. These are the most dangerous tornadoes of all, and spark the common observation of one structure being destroyed while an adjacent structure survives.

Surviving a Tornado

While the only truly safe place from a tornado is underground, heroes have several courses of action which increase the odds of survival. PCs can take refuge in a basement or specially-constructed safe room or get into the structure’s interior on the lowest floor, away from windows and with as many walls between themselves and the twister as possible. If caught outside, they can lie flat in the lowest depression available (such as a culvert or ravine.) A vehicle such as an ATV or Ground Car or a light structure like an Advanced Base (Book 3: Worlds and Adventures) may be death traps and aren’t recommended as shelter.

Of course, the best way to survive a tornado is to listen closely to weather reports for a particular area and then be elsewhere before it arrives.

Aftermath of a Tornado

Twisters can cause great damage, but this is typically along a set path. Thus, a tornado is by nature a local phenomenon. However, an outbreak, or multiple storms and associated tornadoes appearing in a widespread area, can cause extensive damage. Such disturbances on planets with particularly dynamic weather patterns may see outbreaks become regional in scope.

The typical response to a tornado’s aftermath is to locate survivors, render aid to the injured, account for the missing and the dead, and assess the damage with an eye not only to calculating monetary costs, but assigning an EF rating. On worlds with a low Law Level, victimization of survivors by criminals—especially looters—can be a problem.

A tornado can have a large impact on an area’s economy, infrastructure, environment, and even its society. Damage from an EF5 or an outbreak can reach into the billions of credits. Typically only the area directly affected by a tornado bears the costs of recovery. Even an outbreak rarely rises to the level of requiring aid from a nation-state, world or the Imperium. Infrastructure can be greatly compromised, especially the delivery of essential services such as power, potable water, and foodstuffs. If the tornado destroys the main provider of these items, recovery can take years instead of weeks. Environmental damage comes from the destruction of cropland, forests (which can lead to soil erosion and animal migration), and food chain disruption. Facilities that manufacture toxic compounds, if damaged or destroyed, can leak poisons into the ground and water. Tornadoes that become waterspouts can carry hazardous debris with them. Fires sparked in the storm’s wake can wreak secondary havoc, especially if local emergency services have also been compromised. Social disruption can lead to psychological problems such as Post Traumatic Stress Disorder, social unrest in the form of increased crime and rioting, and even mass exodus as a populace decides to relocate to safer places.

Refereeing a Tornado

The following rules are a more detailed version of the rules appearing in “Hazard: Storm!” and replace the tornado rules therein. It’s also geared toward creating classic supercell twisters.

Determine if—or rule that—a thunderstorm is powerful enough to become tornadic. Once the funnel begins descending, it touches down in 1D combat rounds.

Throw 2D-2 for the tornado’s Intensity (i). Apply the result to the following calculations, substituting 1 for 0 except where noted:

Note that there isn’t necessarily a correlation between the size of the funnel and its Intensity.

A direct hit by the funnel inflicts 2i dice of damage per second it is in contact, from dust and debris driven hard enough to penetrate solid objects. (Funnel width×0.28)÷forward speed (round to nearest value)=number of seconds. For example, an Intensity 3 funnel measuring 300 meters across moving at 20kph takes 4.2, or four seconds to pass over an area. Anyone unlucky or foolish enough to be caught in the vortex takes 6D damage each second for four seconds. Armor protects normally, for what it’s worth.

A person in such straits is endangered not only by the shrapnel, but being lifted and thrown. The total direct hit damage calculated above÷the object’s weight in tons=number of meters the object is moved. In the example above, the total of 24D would be used to calculate how far an object would be thrown. `If the object is a person, throw 1D; if it comes up “1,” (s)he is thrown into the path of the tornado, to be thrown again. Repeat this for each result of “1” on the 1D throw.

However, tornadoes have been known—rarely—to leave creatures completely unharmed. Total the victim’s STR, DEX, and END. If the result equals or exceeds the total damage dealt by the funnel, the character suffers no damage, but may still be thrown, as above.

As noted, a vehicle is the worst place to be in during a tornado, but if the heroes are caught in one, it protects its occupants as Combat armor for a number of seconds equivalent to its weight in tons divided by i (round off), thus reducing the damage somewhat. Atmospheric craft instead divide weight by 3i due to their light construction.

If use of the EF scale is desired to help describe the tornado, throw 2D: 2+ = EF0, 6+ = EF1 10+ = EF2, 11 = EF3; 12 = EF4. If a natural 12 results, throw again. If 12 again results, the storm is the dreaded EF5. DMs: +1 if Atmosphere 8+. Note that the vast majority of tornadoes are EF0-1.

Forecasting a Tornado

Predicting tornadic weather is an inexact science at best. The storms are completely unpredictable; they may not appear even when conditions favor their development, and may form even when conditions don’t warrant it. They may not necessarily move in a predictable fashion: they’ve been known to stand still, make abrupt turns, and even backtrack. And they can appear and disappear with disturbing suddenness.

Still, to save lives, science endeavors to understand them. Again, the best way to survive a tornado is not to be near one in the first place. The key to accomplishing this is earlier prediction. Meteorologists have long focused their efforts on lengthening the time between a prediction of a tornado and its manifestation. Imperial science has helped; tornadoes can be predicted on worlds prone to them with high accuracy and long prep times. The tools used to do so haven’t changed, only the technology behind them.

“I Happen to Know Something About Tornadoes”

PCs with certain skills and backgrounds can be very useful in an adventure or campaign featuring tornadoes. They typically will have received some measure of training involving the study, prediction or survival of tornadic weather.

PCs hailing from words with tornadic weather will be familiar with the proper safety techniques. They can advise other heroes on how to take cover from the storms, signs that show if one is imminent, and whether an intended survival action is a good idea. As noted before, primitives still attuned to nature can often sense innately if tornadoes are likely to develop.

Scouts receive a broad meteorological overview as part of their planetology and survey studies. Scientists certainly have the option of specializing in atmospheric mechanics or meteorology. A subset of scientists gets up close to the storms and attempt to insert remote sensing devices but many such “storm chasers” are motivated more from the adrenaline rush than pure science.

Two skills can dovetail with tornado knowledge. Pilot skill must have knowledge of wind shear and atmospheric conditions favorable to safe flights, and any PC with Survival skill has at least some knowledge of tornado safety and avoidance.

A Tornado’s Impact on the Game

The appearance of a tornado in an adventure can serve many purposes: as a random or background encounter; as an unthinking, unfeeling adversary; as a spur to adventure; as a device to provide clues; or even as a deus ex machina should the heroes find themselves in over their heads. Regardless of how the referee uses a tornado, the result should be to enhance the adventure, not derail or destroy it.

Ship’s Locker

THOR (Tornado Haven Optimally Restrained)
(TL10) Cr10,000. This is a higher-tech expression of a safe room. It uses gravitics technology to keep itself anchored to the enclosing structure’s foundation and deflect flying debris. Its armor is equivalent to Combat for any debris that does get through.
Tornado Reconnaissance Drone
(TL9) Cr89,500. A remotely-piloted, lifting-body robot designed to enter a tornado funnel (a maneuver called “punching the core”) and take readings and measurements. Basic remote control range is 5 kilometers. Some models have wireless communication systems that allow them to be controlled at longer ranges, even from orbit. At Tech Level B+ low-level AI takes the place of remote control in some models. Against debris damage, its armor is equivalent to Cloth. Weighs 400kg.