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What's the difference between a hurricane and Alaska's mega storm?The huge weather system that began to lash Alaska's western coastline with wicked strong winds and high water overnight Tuesday is what meteorologists call an extra tropical cyclone. Though intensely powerful and potentially destructive, it is not a hurricane. "It's a completely different kind of storm. A lot of the impacts are the same but scientifically it's a fundamentally different process within the atmosphere," explained Andy Dixon, a meteorologist with the National Weather Service in Anchorage. It's a cyclone because it's a mass of inward spiraling winds driven by a low pressure system, and it's "extra tropical" because it occurs outside the tropics. Hence the title "extra tropical cyclone." But when you live in the nation's most remote communities that lace the Bering Sea and Chukchi coastlines, hunkered down as category-3 hurricane force winds pound your home, the technical distinction doesn't matter much. "It's a horrible storm and in some ways it is comparable to a hurricane," Dixon said. The fact that the storm is massively wide -- spanning nearly 1,700 miles -- and is delivering sustained, high speed wind gusts certainly gives it a hurricane-like signature in terms of its impacts, worsened due to the cold temperatures and blizzard like conditions accompanying it. But from a scientist's perspective, it's not too different from the weather patterns that bring routine thunder and snow storms to middle America. "This one coming through now is certainly a real doozey. But it is not unheard of. These are the same kind of low pressure storms as we see in Colorado or New England -- but they tend to be strong in the Bering Sea," said Mark Serreze, director of the National Snow and Ice Data Center in Colorado. No ice makes a differenceIt's been nearly 40 years since a storm of this magnitude rattled Western Alaska. Like now, a November storm in 1974 also caused flooding, most notably in Nome. Back then the surge caused millions of dollars in damage, notable because at the time the state's seaside communities also had a protective build-up of winter ice to help safeguard their beaches and towns. The ice helps subdue the force of incoming waves. This year, however, most of the Bering and Chukchi Sea coasts are ice-free. Without that buffer, forecasters expect the storm to cause widespread flooding and erosion. The equation is simple: the longer winds are able to blow unencumbered over open water, the larger and more powerful the waves they will generate will be. While the loss of sea ice is driven by climate change, Serez says it shouldn't be blamed for this storm's force. "To say that the formation of the storm or intensity of the storm is some kind of climate change effect would be irresponsible and incorrect. This is a single event. We have had big storms before," he said. Anchorage is feeling the effectsThe storm battering Western Alaska is so large it's responsible for the light cloud cover experienced Wednesday in Anchorage. "This is an enormous storm," Dixon said. One of the main scientific differences between hurricanes and the current Alaska storm is how the storms feed themselves. The Alaska storm is drawing energy form the jet stream circulating some 15,000 to 20,000 feet above the earth. Hurricanes pull energy from warm ocean water. Unlike a hurricane, which has many bands of spiraling air on all sides, the storm hitting Alaska has one dominant band, recognized as the weather front it's generating. The Alaska storm is also different from something called a polar low, which shares features with hurricanes in that it is fueled by a temperature shift as air is pushed over the sub-zero Siberian plateau into the warmer Bering Sea. In fact, this very kind of weather pattern was developing far offshore Wednesday morning, Dixon said. But storms of that variety are not comparable to the mega system moving over Alaska. "Polar lows can still spin up a very strong storm, but they are small and short lived," Dixon said.
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