I completely agree with Rogerio in one think: weather and climate must not be confused. One is about present facts, the other about tendencies, means, extremes. That's why the question is very pertinent but not correct: this is an extreme that could happen whether climate has changed or not (and if it has, this would be independent of the causes). So it cannot be attributed to climate change. What would be attributable to climate change is the FREQUENCY of such extremes. It is like winning in a Lotto: explaining why some particular guy won a high jackpot (a single extreme) would rely on the number of tickets he bought, how the tickets are distributed to the sellers, how much money accumulated for that jackpot, the drawing mechanics etc; however, explaining why a particular Lotto system results in higher prizes (more extremes) would need to investigate the system (does it accumulate non-won prizes? How difficult is to have no-winner? How much is a single prize (or which is the mean prize...). This is what Rogerio refers to when he cites the Table 1 of the Summary for Policy Makers in the AR5 IPPC report: the confidence of the report on a human contribution to the intensity and duration of drought events or intense tropical cyclones is low. However, this is no surprise as the column to the left shows low confidence of these two kinds of event also low at a global scale for drought or in the long term (centuries) for cyclones. However, to get the real picture better look at the complete table. For instance, this two kinds of events are considered to be Likely and More Likely than not in the future. And, of the seven kinds of event listed in the table, the human contribution is considered very likely for two of them, likely for two more of them, Medium confidence for one and low confidence for two, the ones cited by Rogerio.

So, put it simple, there is no answer to the question because weather and climate are two different things and the explanation of one extreme event can only be related to the particular conditions of that event; only frequency can be related to climate.

The extreme rate of warming in the Arctic region results in a greater loss of ice and snow, less reflection of sunlight, and a faster rate of warming in the Arctic than in the rest of the Northern Hemisphere. Now, the temperature difference between the Arctic and mid-latitude areas helps to drive the jet stream, which drives much of the weather that we experience. Since the Arctic is warming faster than the mid-latitudes, that temperature difference is decreasing and the jet stream is slowing down. A slower jet stream can lead to more frequent and extreme weather events (hurricanes, snowstorms, etc.). In the winter, cold air from the Arctic gets pulled southward and leads to the extreme cold that the midwest is experiencing.

Bahram.

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I'm skeptical of the CO2 be the most important driver of climate, and how some skeptics and AGW alarmists could take this opportunity to say that the current cold wave in the USA is an example of cooling and not heating. I would be lying in the same way that when the moment occur a heat wave outstanding and the alarmists use to illustrate global warming.

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Do not confuse WEATHER with CLIMATE, extreme events occur in situations of greater or lesser global temperature. If we consider that the climate warms as a whole or with small gradients difference between ocean and land, any cyclical disturbance (Atlantic Multidecadal Oscillation or AMO its associated North Atlantic Oscillation NAO Pacific Decadal Oscillation PDO, El Niño and other) are more important to create imbalances between parts of the earth and cause extreme events than the variation caused by differential heating or cooling.

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If the data looks IPCC AR-5 (Table SPM.1), you will see that the correlation of extreme events such as heavy precipitation, drought, cyclone activity with human contribuition are considered medium to low confidence , since heat waves that are considered Likely looking at the references that support these conclusions will see that they are relatively short compared to the period of the AMO.

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In the current situation of the negative phase of the NAO is there really a shift of the jet stream further south allowing cold air masses penetrate the USA and Canada. Ski lovers observed from the months of September and October the conditions of this oscillation, it is almost certain that a negative phase indicates abundant snow on the ski slopes.

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Jeff when he quoted the jet stream most southerly was correct, however the reason for the variation of this migration that is incorrect.

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The climate and weather are controlled by the Oceans and their variations (and long or short periods), but the period may be the same one to two years (El Niño and La Niña) and decades (AMO, PDO, NAO) or mesmo1500 years as the Great Ocean Conveyor Belt!

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Now if you want to take an alarmist position from cold winters that can succeed in this, we might think of the Laurentine Ice Sheet rebuilding, so this would be a major tragedy.

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I completely agree with Rogerio in one think: weather and climate must not be confused. One is about present facts, the other about tendencies, means, extremes. That's why the question is very pertinent but not correct: this is an extreme that could happen whether climate has changed or not (and if it has, this would be independent of the causes). So it cannot be attributed to climate change. What would be attributable to climate change is the FREQUENCY of such extremes. It is like winning in a Lotto: explaining why some particular guy won a high jackpot (a single extreme) would rely on the number of tickets he bought, how the tickets are distributed to the sellers, how much money accumulated for that jackpot, the drawing mechanics etc; however, explaining why a particular Lotto system results in higher prizes (more extremes) would need to investigate the system (does it accumulate non-won prizes? How difficult is to have no-winner? How much is a single prize (or which is the mean prize...). This is what Rogerio refers to when he cites the Table 1 of the Summary for Policy Makers in the AR5 IPPC report: the confidence of the report on a human contribution to the intensity and duration of drought events or intense tropical cyclones is low. However, this is no surprise as the column to the left shows low confidence of these two kinds of event also low at a global scale for drought or in the long term (centuries) for cyclones. However, to get the real picture better look at the complete table. For instance, this two kinds of events are considered to be Likely and More Likely than not in the future. And, of the seven kinds of event listed in the table, the human contribution is considered very likely for two of them, likely for two more of them, Medium confidence for one and low confidence for two, the ones cited by Rogerio.

So, put it simple, there is no answer to the question because weather and climate are two different things and the explanation of one extreme event can only be related to the particular conditions of that event; only frequency can be related to climate.

I would second Regerio opinion.

I recently read that during the current arctic blast no records were broken--I wasn't able to find the source, but I have seen no reports of new records. Events such as these have a real positive side that is often ignored. An Associated Press story by John Flesher indicated that additional precipitation helps raise water levels in the Great Lakes, protect shorelines, kill invasive insects like the emerald ash borer and gypsy moth, slow the spread of some invasive species like kudzu, and make Florida oranges sweeter. It may even remind humans that there is nothing unusual about weather variability and extremes.

Charles.

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In my State (Rio Grande do Sul) has made colder winters. What are the consequences? Increased tourism in our mountain region, especially tourists from Northern Brazil where temperatures of 15 ° C lead the ladies put fur coats, and the second benefit, wheat production increased a lot!

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Yeah, that thing about increased wheat production is what the then prime minister of Russia Vladimir Putin said as a benefit of climate change (that, by the way, he doubted). He did not repeat that after the huge wildfires of that very summer.

What I mean is that climate change sure results in local benefits in specific places and economical sectors, but they are largely overcome but the negative effects in those very places. You can read that in the IPCC AR4 WGII (AR5 WGII is still not released)

http://www.ipcc.ch/publications_and_data/ar4/wg2/en/contents.html

or in the AR4 Synthesis Report

http://www.ipcc.ch/publications_and_data/ar4/syr/en/contents.html

It's noticeable that the Arctic Dipole (pressure gradient between Kara sea and Canada/Greenland) tends to go positive at solar minimum, and has gone more strongly and frequently positive during the long solar minimum around 2009 and the following low cycle 24.

This tends to bring southerly winds off the Pacific in the Asian quarter and Northerly winds off the pole into the Atlantic US/European quarter. I don't think this is the whole explanation, but it's certainly a strong contributing factor.

Well, Roger answer is a good example of a (partial?) explanation of a single extreme. I will assume it is correct (not my field, so I have no idea). Lets go further and assume that in the next 20 years we have five of this situations of Northern air masses pushing south, and that always the best explanation is the one given by Roger. From the climate point of view the question would be why the frequency of these events has increased, i.e., why the Artcitc Dipole goes more strongly and frequently positive during solar minima.

If you regard climate change as best manifest by disruptions in seasonal jet stream patterns then polar vortex intrusions, which are a deformed rossby wave (jet stream), might be expected given the rapid heat content we are adding to the surface ocean. The surface ocean coupling to the atmosphere is largely responsible for determining seasonal jet stream pattern. Human activities are adding energy (at increasing rates) to the atmospheric/oceanic interface and that ultimately will affect planet vorticity and the "shape" of the Rossby wave pattern about the north pole.