Visualizing Wind Speeds
We recently learned about the Beaufort Scale. In the early 19th century, Sir Francis Beaufort sought to create an empirical system for describing wind speeds, in an effort to make communication about conditions useful to mariners.
As the scale matured, it moved from informing dedicated sailors to anyone on the water to anyone on land or sea who experiences winds. While the updated version allowed one person to objectively express to another person the weather conditions, human perception of extremes is still notoriously dodgy. Ask someone to estimate the height of a tall tree and chances are the produced number will be far higher than the actual dimensions. As it turns out, the same is true for wind speed.
According to a study conducted by the University of Florida and the Federal Alliance of Safe Homes, people were fairly accurate with their perceptions of wind speeds at lower velocities but tended to misfire when actual speeds were higher. Looking at the Beaufort Scale in detail might explain part of this dichotomy. Most people likely have a decent idea of how winds at extraordinarily high or low speeds might affect the environment, but what about the spots in the middle of the spectrum?
The mirror-like waters and vertical smoke of Force 0 winds are obviously imaginable to everyone. Level 1 – which corresponds to winds of 1 to 3 miles per hour – creates ripples on water and can blow smoke but not a wind vane; this level feels intimately knowable. Likewise, the powerful forces of hurricanes and tornadoes stir the imagination toward devastation. One does not need to have personally experienced such speeds to understand what they might look like (distinguishing a Category 4 hurricane from a Category 2, for example, might be a different story, but that’s beyond the Beaufort Scale). The system’s final stop is Level 12’s Hurricane, which features speeds over 72 miles per hour. In between the 3 mph of Level 1 and the 72 mph of Level 12 lie 10 distinctions for a spread of just 69 miles per hour. This stretch implies that relatively subtle differences in velocities can have a big impact on the physical world.
Wind speeds up to 40 miles per hour are relatively common. For me, at least, this commonness led to the imagined need for higher velocities in order for a storm to be destructive. In fact, to reach the point of Level 7 on the Beaufort Scale – a point at which winds can put whole trees in motion, take umbrellas to the void, and make walking difficult – the wind only needs to reach 32 miles per hour. Cars drive more quickly on many city streets. Though a 30-mph reading is certainly windy, I would not have lumped it into the realm of a full tree swaying. If I saw a giant maple flapping around, my estimation would have likely been much higher than 30 or 40 miles per hour. According to the scale, structural damage begins at the 47-mph tier, Level 9. Obviously, 47 miles per hour is a rough wind but my guess for damage would have been higher.
In addition to undervaluing the “lower” speeds, cramming 10 levels between paltry breezes and catastrophic speeds means it’s likely difficult to discern disparities between speeds if we don’t have a scale to help us. What does a 20-mph gust look like in the trees? How does it change at 30 or 40?
With the caveat that the following examples are the result of self-reporting, which the University of Florida/FLASH study displayed is likely inaccurate, let’s attempt to visualize what some different velocities look like using mostly the same framework: trees.
In the video above, we start with speeds of 20 miles per hour. Previously, I would have pegged this reading to be on the tame side, but the footage shows just how much a tree is caught in Level 5 wind on the Beaufort Scale. This example already displays that speeds can be damaging at points much lower than I would have predicted.
Bumping the power up just 10 miles per hour has a relatively dramatic effect on the trees. They begin to move into the airspace of others. Once again, I would have pegged this behavior from speeds much higher.
The next scenario has some scientific weight to it, as the reporter totes a handheld anemometer. A tropical storm was on the way in, packing winds in the 40-mph range. Though we cannot see any trees comparable to the previous videos, this example produces weather that my imagination would have produced with speeds much higher.
Once winds hit 50 miles per hour, reaching Beaufort Level 9, inland trees really start to take a beating. At this tier, structural damage can begin to happen to residential buildings. The exact speed in the following clip is not necessarily clear, especially because the effect is amplified by precipitation, but one can start to see how dangerous these speeds can be. A bit counterintuitively, this zone seems to fit my perception of 50 miles per hour better than the previous several scenarios. Perhaps 50 just sounds like a big number.
The next illustration is fascinating because it places the “calm before the storm” directly next to massive winds. We can’t be certain the reported 70-mph figure is accurate, but the way the trees behave certainly displays it might be possible. Interestingly, the trees seem to oscillate in a chaotic fashion at these speeds in a way they did not at 30 miles per hour. At the lower velocity, the trees seemed to move back and forth, giving to the wind and then snapping back into shape, only to have the process repeat. At 70, the physical matter of the tree seems to lose its shape completely, though it does not give way.
We go treeless another time in the following video, as we visit one of our favorite spots, New Hampshie’s Mount Washington. This crag is one of the windiest places on the planet and it’s a great one to illustrate the next velocity tier. The piece from the BBC does a great of showing how lower speeds can move objects I would have guessed would require higher winds, before demonstrating what 80+ miles per hour can do to a walking human.
Of course, 80 miles per hour is child’s play for Mt. Washington. A pair of scientists at the weather observatory on the peak produced a video on the effects of winds just shy of 110 mph. As you can see from the thumbnail, levitation isn’t necessarily a magic trick!
At Beaufort Level 11 – between 64 and 72 miles per hour – winds reach a point that is “very rarely experienced inland.” In fact, the dramatic events captured in the subsequent video can happen at a rung below that point, according to the official descriptions. When tornados or derechos subject inland areas to speeds usually only felt on coasts during cyclones, things can get ugly. Incredible to watch this awesome power:
During major hurricanes and tornados, the winds can get far worse.
Putting it all together is the national treasure that is Jim Cantore, of thundersnow fame. He hopped into a wind tunnel in an attempt to experience the gamut of winds, from the tepid to Category 5 hurricanes.
At some point, speeds seem to break the human ability to perceive the differences, though this threshold seems to be fairly high. When we recently encountered 55-mph winds on Mt. Marcy, they felt big but the number did not register as anything quite tenacious in my mind’s eye. However, after some research into the Beaufort Scale and comparing videos of different speeds, I’ve landed on a new perspective. At that rate, structural damage can occur and it’s right on the brink of being able to uproot trees. Thankfully, on the summit of Mt. Marcy, being in the path of uprooted trees is not a concern.
My threshold for what constitutes a high wind apparently needs to be lowered!
Further Reading and Exploration
Wind Speed Perception and Risk – National Library of Medicine
Beaufort Wind Scale – National Oceanic and Atmospheric Administration
Beaufort – National Meteorological Library and Archive