It is easy for me to suspend belief when I am watching an Avengers or Star Wars movie. However, whenever I watch a movie about weather or climate, the scientist in me is always lurking. My wife and I saw Twisters yesterday. The moviegoer in me watched it for the storyline and action. However, I am also a meteorologist, past president of the American Meteorological Society, and director of an atmospheric sciences program at a major university. This means that I was also consuming the movie from a scientific lens too. Here is my attempt to explain the science, terms, and more in Twisters.
The first installment, Twister, is an iconic movie. Virtually any meteorologist my age or younger places that film on their “Mt. Rushmore” of movies. It produced a new generation of students interested in meteorology and storm chasing. Meteorology or atmospheric sciences departments swelled with new enrollments and so did the roads of the Great Plains during the spring. I am bracing for a similar response after Twisters.
My wife Ayana thoroughly enjoyed the movie as a casual viewer going into the theater with no scientific expectations. It will appeal to most moviegoers seeking the formulaic Hollywood mix of action, hyperbole, and a love story. I also liked the movie but was also taking a few notes on my phone. Shhhhhh, don’t tell the theater manager since they warn you incessantly about using your phones during the movie.
Twisters, which joins a growing list of nostalgic movie offerings this year, starts with a flashback to a group of young meteorology researchers trying to “disrupt tornado dynamics” in a violent storm. In other words, they were trying to dissipate the tornado using super absorbent polymers to “choke off” the moisture in the storm. It was an idea hatched by one of the main characters, who like many of us had a passion for weather since middle school. What happens next sets up the rest of the movie as the setting fast forwards to current times. Two competing storm chaser teams pursue an outbreak of tornadoes with very different intents. That’s about as far as I want to go with the movie review to prevent spoilers. Let’s discuss the science.
I teach the Radar/Mesoscale Meteorology course at the University of Georgia. It is the exact course in a meteorology program that covers topics featured in the movie. When we discuss severe weather, students always perk up. By the way, the National Weather Service glossary defines a severe thunderstorm as, “A thunderstorm that produces a tornado, winds of at least 58 mph (50knots), and/or hail at least 1″ in diameter.” For tornadic storms to form, I tell my students to remember the acronym SLIM. Let’s break each letter down and connect them to Twisters.
Shear
Wind shear is a change in speed and/or direction in the vertical or horizontal direction. The characters in Twisters often referred to it while assessing whether enough shear was present to support production of a supercell thunderstorm. Though less common than a regular thunderstorm, supercells are typically associated with severe weather in the Great Plains and increasingly in the southeastern U.S. too. The rising, moisture-laden plume in a thunderstorm is called an updraft. Supercells have a rotating updraft called a mesocyclone that precedes a tornado. Be on the lookout for several supercells in the film. I saw both low-precipitation (LP) and high-precipitation (HP) supercells in Twisters. HP supercells can be associated with rain-wrapped tornadoes which can make them particularly dangerous because you cannot see them.
I should point out, however, that not all supercells produce a tornado. According to NOAA, the home of the National Severe Storms Laboratory, “…. Moderate to strong speed and directional wind shear between the surface and about 20,000 feet is the most critical factor.” Wind shear actually serves a couple of purposes. It helps to create the rotating updraft and allows for the storm to be tilted. Why is that important? It allows for coexisting updrafts and downdrafts. Downdrafts, caused in part by evaporating rainfall, are cold plumes of air that rush downward. In a typical afternoon thunderstorm, the downdraft can choke off the moist updraft and “blow” the storm out.
The NOAA website goes on to say, “A separate updraft and downdraft allows the supercell to be long-lived because it reduces the likelihood that too much rain-cooled, stable air from the downdraft region will be ingested into the updraft, causing the storm to weaken.” A key premise of the technique being pursued by our Twisters heroes is to try to starve the moisture out of the tornadic storms using polymers and cloud seeding. I will circle back to that later.
Lift
A source to lift is always needed to initiate storm development. Lifting mechnisms can include fronts, drylines, outflow boundaries, and other entities in which there is a density difference. My kids would often marvel at my “geekdom” when I would mix diet soda and Mountain Dew. Because of the differences in sugar content, they had different densities. It was a fun little experiement, but such density differences are at the heart of many lifting mechanisms in severe weather processes.
Instability
Instability is what allows air to rise once lifted to produce explosive storms. If you have ever taken a ride in a hot air balloon, you are benefitting from instability. The air in the balloon is heated so it becomes warmer than the air that it is rising within. This creates positive buoyancy and the balloon is able to rise. Throughout the movie, the scientists refer to instability. You will also hear them mention CAPE, which stands for Convective Available Potential Energy. Higher values of CAPE provide clues for meteorologists that stronger updrafts are possible.
Moisture
It was interesting to watch the meteorologists in the movie try to pick which storms would have the optimal mix of lift, shear, and instability to produce lasting tornadoes or break through a “cap” of stability. Daryl Hall once said in the song “You Make My Dreams Come True” that the “candle feeds the flame.” The inflow of moist air feeds tornadic storms. I mentioned that a premise of the researchers’ efforts was to starve the storm of moisture and dissipate the tornado. After realizing polymers were not sufficient to do this, the scientists learned from Phased Array Radar (PAR) analysis (more on that in a moment) and detailed computer modeling that they needed to induce “rain” in the storm using cloud seeding. What’s that?
Cloud seeding is a type of weather modification that uses things like silver iodide to “seed” the growth of ice crystals (nuclei) in clouds needed to start the process of rain formation. According to the Desert Research Institute website, “These nuclei provide a base for snowflakes to form.” Did you know that most rain starts out as snowflakes before melting? Yep, they do. While many agencies and countries employ cloud seeding, past and current scientific studies find results to be inconclusive. You’ll have to watch the movie to see what ultimately happens, but the scientist in me definitely had to suspend disbelief.
Other Notable Nuggests From The Movie
Phased Array Radar
I mentioned Phased Array Radar earlier. The use of this technology permeates the storyline in some interesting ways. PAR is an emerging technology. The NSSL website says, “Current weather radars mechanically rotate and tilt the radar dish to sample different parts of the atmosphere.” The phased array radar uses a completely different design. It is comprised of stationary flat panel antennae, “Made up of a grid of fixed antenna elements, and each can transmit and receive a signal.” Why is this valuable? NSSL says, “This means the radar can be controlled to direct its beam only where storms are detected. Focused observations of storms lead to faster updates since the radar does not waste time scanning clear-air regions.” It was cool to see concepts of multiple radars targeting storms to derive air motions. As a graduate student at Florida State University, I worked with one of the pioneers of multiple Doppler radar analysis to detect winds.
Enhanced Fujita Scale
The Enhanced Fujita (EF) Scale is used to rate storms and is mentioned several times in the movie. Unlike the Saffir-Simpson Scale for hurricanes, which is based on real-time winds in the storm, the EF Scale is based on damage. The National Weather Service is the only entity authorized to rate tornadoes. Their website says, “When tornado-related damage is surveyed, it is compared to a list of Damage Indicators (DIs) and Degrees of Damage (DoD) which help estimate better the range of wind speeds the tornado likely produced. From that, a rating (from EF0 to EF5) is assigned.”
Safety
There are several actions taken in the movie that subtly illustrate best practices if you are caught in a tornado. The characters are often seen seeking basements, storm cellars, interior reinforced rooms, or low points. Early in the movie, an important scene involves sheltering under a highway overpass. I have written in the past that overpasses are dangerous because they are places where wind speeds may be higher due to height and funneling of air (and debris) through the narrow passage under the bridge. The National Safety Council has a great list of tornado safety recommendation.
There is a lot more that I could say about Twisters. The movie accurately shows how meteorologists use observations, instincts, and computer models to nowcast or forecast weather. Heck, it even mentioned the Fujiwhara effect, which is when two tornadoes do natural tango with each other around a central point. It also revealed the beneficial and “wild west” sides of storm chasing. In both cases, it’s dangerous. Climate change is real and affecting extreme weather on several fronts, but I would quibble a bit with some of the connections implied about tornadoes. Radar technology is allowing us to detect more tornadoes than in previous decades. However, contemporary research is starting to suggest connections between climate change and tornadic environments.
I was most pleased to see the “human element” in Twisters. I often remind colleagues and students not to “cheer” for storms. They take and change lives. Weather should not be for sport, and human lives should be valued first. The film certainly raised the stakes on that point, and I applaud them.
