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[Slashdot] - Pacific Northwest Bakes Under Once-In-a-Millennium Heat Dome

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As covered earlier today, the Pacific Northwest is experiencing the most severe heat wave in its history, with all-time record temperatures being set in Portland, Seattle, and Lytton, B.C, which just broke the record for hottest temperature ever recorded in Canada at 116 degrees. CBS News says this heat wave "is of an intensity never recorded by modern humans," and by one measure it's "more rare than a once in a 1,000 year event." Meteorologist Jeff Berardelli explains what's causing this "heat dome" and why events like this "are bound to become more common, more extreme and more deadly in the coming years": The heat is being caused by a combination of a significant atmospheric blocking pattern on top of a human-caused climate changed world where baseline temperatures are already a couple to a few degrees higher than nature intended. [...] In the case of this specific heat dome, which is a mountain of hot air stacked vertically through the atmosphere, it is a once in a 1,000 or even 10,000-year event for this particular area. How do we know? It's actually quite simple to explain. The intensity of a heat dome is measured by how "thick" the atmosphere is at a given spot. The hotter the air in that column, the larger the thickness of air in that column, because heat expands. In our historical record of North America's Pacific Northwest this heat dome registers a statistical standard deviation from the average of greater than 4. In layman terms, that means it falls more than 4 deviations to the right of the center of a typical bell curve (shown below) and that equates to values with less than a 99.99% chance of happening. In other words, statistically speaking, there is a 1 in 10,000 chance of experiencing this value. So, if you could possibly live in that spot for 10,000 years, you'd likely only experience that kind of heat dome once, if ever. It is worth noting that our historical record is limited and statistics like this are very sensitive to small changes. But if it seems like an overstatement to say there is a 1 in 10,000 chance of having a heat dome like this, it is certainly not an overstatement to say this is the kind of event you would expect to experience once in 1000 years. So what is causing this heat wave? Like any heat wave, it is being caused by a highly amplified jet stream pattern. These extreme jet stream perturbations are a natural, normal part of the atmosphere. But the climate science community is split as to whether these extreme jet stream perturbations are becoming even more likely because of climate change -- a phenomena known as the wavy jet stream. Along with a more wavy, buckling and slow-moving jet stream, comes a phenomena called "blocking". This is when waves in the jet stream become so elongated that they break off, sit and spin. In this case there is a textbook type of block called an Omega block over the Pacific Northwest because it looks like the Greek letter Omega. Inside this Omega, the heat pools and intensifies. There is a faction of climate scientists who believe that a warming climate -- specifically the Arctic -- results in a more wandering jet stream at certain times of the year. But it is hotly debated; there is an equal amount of research that does not arrive at this conclusion. Mann and his colleagues have been involved in some of this research, in which he finds that a specific type of Northern Hemisphere blocking -- what he calls Quasi Resonant Amplification -- will increase by 50% this century under business as usual human-forced climate warming. "I do indeed believe that the phenomenon we describe in our work played a very important role in the record heat wave," Mann said. As for the lack of consensus in the climate research on the wavy jet stream and blocking, Mann thinks it has more to do with the current state of climate modeling "This is an area where current generation models are NOT capturing a real-world climate connection," Mann explained. Whatever the cause, the result of an extreme jet stream pattern is extreme weather across many parts of the nation and globe. Over the past few days, the central U.S. has seen over a foot of rain with flash flooding along a stalled front. And, starting on Sunday and continuing through most of the upcoming week, the major East Coast cities will also sweat through a heat wave -- although not nearly as intense as the one in the West -- with feels-like temperatures near 100 degrees from Washington D.C. to Philadelphia and New York City.

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