At the moment, some people are probably wondering about the weather, which doesn't seem to fit in with the dream of a White Christmas. For example, the WeatherBlog received the following question: "Hi, can you explain when this warm and sunny bastard weather will disappear? And what does it have to do with climate change if it gets 2 degrees warmer overall? Why is it not -2 degrees in December instead of -5 degrees as it used to be, but +15 degrees for weeks on end? What does global warming have to do with the fact that we have often had a tendency towards a persistent mild south-westerly flow in recent years...?"
Point 1: When will the warm and sunny nasty weather disappear?
Short version: nobody knows for sure. Until yesterday, the two major weather models were very much at odds, but now the European ECMWF model has come closer to the American GFS and also discovered an option for an end to the SW situation. Both now see a high developing roughly over the Baltic and Scandinavia at the beginning of January. This will result in a corrugation, which will also have a cold side, and cold air will advance far to the south on the western flank of the high. Whether this will happen is still quite speculative, but the ECMWF's switch to a more or less joint solution is of course a hopeful sign. At least we would then have a different general weather situation. Whether and where this will actually lead to snow and cold is another question and depends very much on the details. You can't really see them in the crystal ball yet.
Point 2: What does this have to do with climate change? If it's getting 2 degrees warmer overall and it used to be -5°C in December, why is it now not -2°C but +15°C for weeks on end?
Here it's important to distinguish between the very different concepts of "weather" and "climate". Weather is what I notice on my doorstep right now and what will happen tomorrow and the day after tomorrow. Climate, on the other hand, is what happens on average over several decades. Wikipedia puts it like this: "Climate is the totality of all possible weather conditions at a location, including their typical succession and their daily and seasonal fluctuations." The climate at a location is therefore something like the average of all possible weather variations at this location. In order for this to be reasonably representative, we speak of climate when we have around 30 years of data available to calculate this "weather average".
"+15°C for weeks" falls under the heading of weather. Climate change would be a change in the mean value over a much longer period of time, for example a rise in global temperature of 2°C over a period of 150 years. This much-cited increase does not mean that it simply becomes 2° warmer everywhere in the world evenly distributed over the year, but that if you throw the entire world's weather together and average it, you arrive at a value that is 2° warmer than the comparison period. In such a climate average, there is plenty of room for extreme weather at both ends of the scale, including "+15°C for weeks on end" (we won't check now whether this really sums up the current situation accurately).
Point 3: What does global warming have to do with the fact that we have often had a tendency towards a persistent, mild south-westerly flow in recent years...?
Short version: Once again, nobody knows exactly. Apart from a shift in the mean in the context of climate change, it is likely that the frequency distribution of the individual weather events will also change (corresponds to the shape of the curve in the graphs). This can mean, among other things, that the typical weather pattern over the year changes in a particular region, or that there are more extreme events. It may well be that certain weather conditions occur more frequently (or less frequently) over time.
For several decades, a long-term increase in the NAO index has been observed (at least in the winter months), which lies outside the expected natural variability. Accordingly, it is assumed that the increase is due to climate change, which alters the underlying processes. However, it is unclear how the causal relationship works. A high NAO index means strong pressure differences between Iceland and the Azores, which results in a strong westerly drift (westerly weather).
Last year, there was a similar question asking whether stable weather patterns are becoming more frequent. The answer was complicated and not overly meaningful. Unfortunately, the WeatherBlog has no further, decisive findings in this regard. To summarize: There are probably changes in the frequency of certain weather patterns and they may be due to climate change. What the changes look like and why they occur is not sufficiently known.
We still wish you a Merry Christmas and all of us a sustainable onset of winter in the Alps!
Finally, a graphic of the snow cover in the northern hemisphere for the last 10 years. And by the way, you don't say "bad weather".
UPDATE:
In the Weather Center forum, someone has posted preliminary results of their bachelor thesis and comes to the conclusion that SW locations have increased in recent years. There is speculation about the causes in the corresponding thread. Hier lang.
