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What Is the 'Cone of Uncertainty'?

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Cyclone Catarina in the South Atlantic as photographed by astronauts on the International Space Station in 2004. Image credit: NASA via Wikimedia Commons // Public Domain

Weather forecasts are hardly ever perfect. Most of the forecasts you receive these days are pretty solid if you use the right source, but it’s not always a sure bet. Sometimes your friendly local meteorologist uses bad information to arrive at a bad forecast, and sometimes he or she just misses one. Predicting the future inherently involves some level of uncertainty, and some situations are more uncertain than others. Hurricanes are no different. When we look at a hurricane forecast map, the most striking feature you’ll see is the aptly named cone of uncertainty.

A hurricane forecast is conveyed to the public using a map that shows the forecast position of the very center of a tropical cyclone at seven different time steps up to five days out from the initial forecast. The cone of uncertainty, which looks like a quotation bubble emanating from the first point on a hurricane forecast map, is the historical margin of error in a meteorologist’s forecast track for the center of a tropical cyclone.

The forecast track and cone of uncertainty for Hurricane Igor in September 2010. The hurricane’s center stayed within the cone of uncertainty for almost its entire lifespan. Image: National Hurricane Center

At the end of every hurricane season, meteorologists at the National Hurricane Center look at all of the forecasts they made for storms in previous years and average out how far off their forecasts were from the actual location of the tropical cyclone. They average out and compile these errors for every time step in the forecast period all the way out to five days from the initial forecast. When you plot their average track errors on a map using a sequence of circles, the smoothed-out end result is the cone of uncertainty we’re all familiar with.

The center of a tropical cyclone typically stays within the cone of uncertainty 66 percent of the time, which also means that it strays outside of the cone 34 percent of the time. Tropical cyclone forecast tracks are much better today than they were in years past, but track error naturally grows with time as confidence in a forecast track decreases. The National Hurricane Center is only off by an average of about 35 miles when they predict the location of the center of a tropical cyclone 12 hours out. That average error grows to 97 miles two days out and goes all the way up to 273 miles five days out. To give you an idea of how wide the cone of uncertainty is five days out, it’s just roughly the distance you would cover traveling from Boston to Philadelphia.

The cone of uncertainty does not show you the confidence that forecasters have in that particular forecast. It shows you neither the size nor the total extent of the impacts a tropical cyclone will have. It doesn’t matter if it’s a 500-mile-wide hurricane or a 20-mile-wide tropical depression; the cone only applies to the very center of a hurricane, and it only tells you how far off forecasters were when they predicted the track of previous cyclones. You aren’t necessarily safe if your location falls outside of the cone of uncertainty, nor does it mean that areas inside the cone are definitely going to get blasted. Understanding the size and impacts of a tropical cyclone requires more context than one simple map can provide you.

Most tropical cyclones form and move along tracks that don’t stray too far from their predicted paths. A sudden jog to the west or east usually isn’t too much of an issue, but even a small deviation in course could be a big deal during complex or high-risk situations.

The forecast track and actual track of Hurricane Joaquin in October 2015. Map: Dennis Mersereau

The most common reasons storms deviate from their predicted paths are that they’re extremely weak (and subject to erratic movement) or they exist in a complicated setup with lots of moving parts. One of those latter situations occurred in 2015 during Hurricane Joaquin. The major hurricane formed over the Bahamas in a complex environment that would ultimately dictate whether it would make landfall in the United States or swirl harmlessly out to sea. On October 1, meteorologists issued a forecast that showed the storm approaching the Mid-Atlantic coast of the United States. Most of the models misread the weather pattern that week and the storm wound up trekking out to sea, causing Hurricane Joaquin’s ultimate path to fall almost entirely outside of the cone of uncertainty for that forecast.

If you find yourself in or near the cone of uncertainty four or five days out, that’s your cue to keep tabs on the situation and make preparations in case you have to secure your property or evacuate to safer ground. It’s time to act if you’re still in the cone a few days out. Watches and warnings will already be in effect by then and you’ll have plenty of information from the experts telling you what you should do in order to stay safe.

Great Britain's Last Snow Patch Is About to Disappear Completely for the First Time in a Decade

Until recently, it was easy to find snow in Great Britain at any time of the year—you just had to know where to look. In previous Septembers, the island has been home to as many as 678 snow patches, residual pockets of snow and ice whose climates and topographies keep them frozen through the summer. This year, though, only two of Britain's snow patches have survived the summer. And the island is now on track to be completely snowless by the end of the season, Atlas Obscura reports.

Snow patches vary in size and durability, with some melting completely by late summer and others remaining a permanent fixture of the landscape. Garbh Choire Mor—a steep glacial depression on top of Scotland's third-highest mountain, Braeriach—contains two of the oldest snow patches in Britain, known as the Pinnacles and the Sphinx. The Pinnacles snow patch dissolved into a puddle earlier this month, and the Sphinx snow patch, the last surviving snow patch in Great Britain, is expected to do the same in the next few days.

Scotland experienced uncharacteristically hot weather this summer, with temperatures creeping into the low 90s as early as May. But more significant than the sweltering summer was the dry winter that preceded it. Below-average snowfall last year meant this year's snow patches were already smaller than usual when temperatures started heating up. If the Sphinx snow patch does vanish before winter arrives, it will mark the first time in over a decade and just the sixth time in the last 300 years that England, Scotland, and Wales are without a single patch of snow.

The Sphinx snow patch, though currently a measly version of its previous self, is still visible for now. But Iain Cameron, a veteran "snow patcher" who writes an annual report on snow for the UK's Royal Meteorological Society, says it could be gone as soon as Wednesday, September 20.

He's currently camped out on Garbh Choire Mor, waiting to document the patch's final moments. You can follow his updates on Twitter.

[h/t Atlas Obscura]

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Matt Tillett, Wikimedia Commons // CC BY 2.0
‘Harvey the Hurricane Hawk’ Returns to the Wild
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Matt Tillett, Wikimedia Commons // CC BY 2.0

Among the devastating news that came out of Houston during the last weekend in August, there was one video that warmed the hearts of those following Hurricane Harvey. A Cooper's hawk startled Texas cab driver William Bruso after climbing into his car and hunkering down before the storm. Now, after receiving care from both Bruso and local wildlife experts, the Associated Press reports that "Harvey the Hurricane Hawk" has been released.

As the video below shows, Bruso assumed that the bird sensed the severe weather approaching and sought refuge in his cab. "He seems to be scared," he said. "He doesn’t know what’s going on. Hurricane Harvey is getting ready to barrel down through over here, and he doesn’t want to leave."

Veterinarians at the Texas Wildlife Rehabilitation Coalition Wildlife Center later learned that the hawk—which is actually female—had suffered head trauma, likely by flying into something, and this had left her unable to fly. After she refused to leave his side, Bruso took her into his home, fed her chicken hearts, and let her spend the night. Liz Compton of the rehabilitation center came to pick her up the next day.

Following a week and a half of medical care, Harvey the hawk has returned to the skies. According to TWRC, the animal likely wouldn't have survived the storm if she hadn't been given shelter. Texans hoping to catch a glimpse of the viral celebrity may be able to spot her above Oak Point Park in Plano, Texas, where she was released on September 13.

[h/t AP]


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