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A look at weather extremes and the big-picture climate connections.

Freak Pattern Brings Europe Record Cold and Snow

Originally published on Washington Post's Capital Weather Gang blog

One of the fiercest beginnings to winter on record has slammed Europe with relentless assaults of bitter cold and heavy snowfalls. The unusually wintry weather gripping Europe as well as the cold plaguing the eastern United States are linked by a historically strong weather system locked over Greenland.

Map of atmospheric pressure departures from average (geopotential height anomalies) from December 1 to 18, 2010. Credit: NOAA.

In Europe, the strange weather pattern has caused mayhem for holiday travel. Over the weekend, airport and ground transportation disruptions were widespread, from London's Heathrow Airport - one of the world's busiest hubs - to Frankfurt International Airport and the German Autobahn. According to the The Guardian newspaper, Frankfurt airport workers resorted to dressing up as angels in an attempt to calm the situation when crowds of stranded passengers, frustrated by lengthy delays and flight cancellations, became unruly. Heathrow, meanwhile, was closed to arriving aircraft on Sunday, after being closed altogether on Saturday, according to several news reports. More heavy snow is forecast for London yet again today according to the UK Met Office.

BAA spokesman Andrew Teacher told CNN: "These are absolutely ... freak weather conditions ... We've not seen a storm like this in 20 years."

So what has been causing this freak winter weather onslaught in Europe, and the colder-than-average conditions in much of the eastern U.S., including Washington? 

There is a very strong "blocking pa...

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Time-Lapse View of 2010 Hurricane Season

The 2010 Atlantic Hurricane Season ended on November 30th with the season tied for third place in terms of the number of named tropical storms and hurricanes — 19. Of these named storms, twelve were hurricanes, and five were major hurricanes of category three strength or greater. Yet despite this above average activity, the United States was spared a direct hit from a hurricane, because weather patterns repeatedly blocked storms from approaching the coast.

You can actually see how storm after storm was kicked out of bounds into the open Atlantic, or confined to the southern Caribbean Sea, thanks to a new visualization of the entire hurricane season from the U.S. National Oceanic and Atmospheric Administration (NOAA).

This movie shows GOES-13 infrared satellite imagery from June 1 through November 30, the official extents of the Atlantic Hurricane Season. Credit: NOAA

As the video plays, watch how fronts and low pressure centers (they show up as swirling cloud masses on the satellite images) repeatedly push off the East Coast, accompanied by strong upper level winds that deflected several tropical storms and hurricanes (their names pop up in the video) out to sea, or in the case of Hurricanes Earl and Igor, northeastward into the Canadian maritimes. Be careful though, the video can be mesmerizing, especially for fellow weather/climate nerds out there.

From this movie, as well as the raw statistics from this season, it's clear that the U.S. was extremely...

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Some Heat Waves Can Be More Harmful Than Others, Study Says

By Alyson Kenward

Heading into this last week of November, when the air is cool and the daylight hours are growing shorter, the idea of a heat wave might sound like a pretty good thing. But it was only a few months ago, back in July and August, that many parts of the country sought relief from long spells of abnormally hot weather. And the heat waves that hit the entire Atlantic coast were relatively mild compared to record-breaking temperatures felt elsewhere around the world this past summer.

Record high temperatures for 17 nations that have broken their national records so far in 2010. Previously, the largest number of countries to break such records in a single year was 14, according to Weather Underground and The Guardian newspaper. If verified, the record set in Pakistan would also stand as the warmest temperature ever recorded in the continent of Asia.

Thousands of deaths were attributed to the most extreme of these summer heat waves, like those in Pakistan, Russia and throughout the Middle East.

Now a new study from Yale University has put some some real numbers on the health risks from U.S. heat waves. In a review of heat waves in 43 American cities between 1987 and 2005, environmental scientists Michelle Bell and Brooke Anderson found that there is a slight but significant increased risk of dying during a heat wave, and that the risk can increase considerably if high temperatures persist for many days or affect areas where people haven't adapted to warm weather by, for example, commonly adopting air conditioning.

Also interesting was the finding that heatwaves occurring early in the summer were found to carry relatively larger risks for human mortality than heat waves with a later onset. In a press release for the new study, published in the journal Environmental Health Perspectives, Bell said:

...

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Southeast Rainfall More Variable as Climate Warms

(Originally published on Washington Post's Capital Weather Gang blog)

In recent years the southeastern U.S. has had a string of summers with unusual amounts of rainfall. There was the withering drought in 2007, during which Georgia Governor Sonny Perdue famously held a prayer service for rain. This eventually worked — albeit too well. Late last summer the drought-stricken region was hard hit by record flooding.

A new analysis of six decades of weather and climate data finds that such extreme summers are becoming more common in the region, due to shifting atmospheric steering currents that appear to be related to manmade global warming.

The study, published in the early online edition of the Journal of Climate, investigates a key driver of summertime weather in the Southeast — the Bermuda High, referred to in the study as the "North Atlantic Summertime High" or "NASH." This High Pressure cell is typically centered in the vicinity of Bermuda, and often acts as a heat pump along the eastern seaboard, drawing warm and humid air up the coast throughout the summer. (You have the Bermuda High to thank for many of our summer heat waves in Washington).

By analyzing precipitation, wind, and humidity observations, along with data of the height of pressure surfaces aloft, the researchers found the western extent of the High pressure ridge has crept closer to the continental U.S. in recent decades, at the rate of 1.22 longitudinal degrees per decade. During that same per...

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Historical Perspective on the Russian Heat Wave of 2010

By Heidi Cullen and Claudia Tebaldi

The summer of 2010 brought intensely hot weather to large portions of the northeastern U.S., central Europe, and Russia. Russia was especially hard hit as a heat wave — with daily high temperatures hitting 100°F — contributing to the deaths of as many as 15,000 people in Moscow while wildfires tore across more than 2,900 square miles in the central and western part of the country. Drought accompanied the record high temperatures decimating more than a quarter of Russia’s grain harvest. Economists estimated the grain losses cost the Russian economy upwards of $15 billion dollars.

As climate scientists continue to study the underlying dynamics of this extreme heat event in order to better understand the extent to which human-caused climate change may have played a role, we wanted to put the Russian heat wave of 2010 into historical context. With that in mind, we collected temperature data from Moscow for July 2010 as well as summer (June through August 2010) and compared it to every year since 1950. (Our analysis is similar to that employed by Schär et. al in their 2004 Nature paper). 

We sought an answer to the question: how significant was the departure of the 2010 values from the typical summer temperature in Moscow?

Probability of June, July and August average temperature anomalies in Moscow, Russia since 1950.
This image shows that the average temperature in Moscow for summer 2010 was significantly hotter than...

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