Change in snow cover probability on Christmas Eve Europe - Changing White Christmas Europe.

Chances of a White Christmas in Europe: Declining Snow Cover Trends on Christmas Eve

The magical feeling of Christmas is often associated with a blanket of snow, transforming landscapes into winter wonderlands. But how common is a snowy Christmas in Europe these days? In this article, we dive into the likelihood of experiencing a white Christmas across different regions of Europe. We’ll also take a close look at the trends: is the chance of a snowy Christmas Eve on the decline? If you’re wondering where to go for the highest probability of a white Christmas, or you’re just curious about how these odds are changing in your area, you have come to the right place.

Check the white Christmas probability in US here.

To explore the probability of a white Christmas, we turned to ERA5 reanalysis data. With many European countries celebrating on Christmas Eve (24th of December), we focused on whether there’s a snow cover on this day at 18 UTC. This corresponds to 18:00 local time in places like Iceland, the UK, and Portugal, 19:00 in most of Western and Central Europe, and 20:00 in regions like Finland and Eastern Europe. The choice of this specific time aligns with the widespread tradition of evening celebrations on the 24th. However, it’s worth noting some countries have different customs. If you’re interested in details of the methodologies behind our findings and what reanalysis data is, you can find more about this at the end of this article.

Probability of a white Christmas in Europe

In our current climatological period (1991-2020 average), a snow cover on Christmas eve is more or less guaranteed in much of Lapland, the Scandinavian highlands, the elevated regions in Iceland, the higher peaks of the Alps and Pyrenees and even the highest peaks in the Balkan countries and Turkey, as indicated by the purple colors in the figure below.

As a general rule, the further you venture towards Europe’s southwestern coast, the slimmer the chance of a white Christmas. However, local effects – especially elevation (in hilly and mountainous areas) – can somewhat compensate for this and turn the tide in favour of snow on Christmas eve.

Snow Probability on Christmas Eve (climatology 1991-2020) -White Christmas in Europe - Christmas Snow Chance
Snow probability on Christmas Eve in the climatological period 1991 2020

Change in snow probability on Christmas Eve in Europe

Rewinding to an earlier climatological period (1951-1980), Christmas Eves in Europe were (much) more likely to be snowy. Back then, a blanket of snow was almost a certainty across most of Scandinavia, Finland, and parts of the Baltic States, Belarus, and Eastern Europe’s mountainous regions. In the Alps, the elevation for guaranteed snow on December 24th was much lower, making a white Christmas a more common occurrence in more places. The same goes for the Pyrenees.

In Germany, the chances of snow ranged significantly (from 25-70%, with even higher probabilities in mountainous regions) but were much higher than is the case nowadays. Most of Eastern Europe basked in a 60-90% likelihood of experiencing a snow cover on Christmas Eve.

Snow Probability on Christmas Eve (climatology 1951-1980) -White Christmas in Europe - Christmas Snow Chance
Snow probability on Christmas Eve in Europe during the climatological period 1951 1990

Snow in Europe on Christmas Eve much less likely

When comparing snow probabilities between the two aforementioned climatological periods, a clear pattern emerges: in our current climatological period, the likelihood of a white Christmas has dropped substantially across most of Europe. This decline stretches from Spain to Eastern Europe, and from Finland down to the Mediterranean. The most pronounced reductions in snow probability are found in Eastern and Central Europe, particularly in areas like Germany, Poland, the Balkan region, parts of the Alps, and Southern Sweden. Here, we’re witnessing enormous decreases, ranging from 20 to 40 percentage points (%pt), and in some localities, the drop is as steep as 50%pt. Regionally, in places such as the lower parts of the Alps, southern Germany, Massif Central, the Balkan and small areas in Poland even show a decrease of more than 50%pt. Yet, it’s not all downward trends; a few regions actually show a slight increase in the likelihood of snow compared to the past.

A percentage point is a unit of measurement used to express differences in percentages. E.g. moving up from 40 percent to 44 percent is an increase of 4 percentage points (although it is a 10-percent increase in the quantity being measured).

Change in snow cover probability on Christmas Eve Europe - Changing Chances of White Christmas Europe.

Higher likelihood of white Christmas in the UK?

In some areas of Europe, including parts of the UK, our analysis indicates a subtle uptick in white Christmases. However, it’s important to note that this increase must be understood in the context of historical rarity. In regions where snowy Christmases have historically been infrequent, even a small number of snowy events can disproportionately influence the overall trend. This is a classic example of a low signal-to-noise ratio, where weather variability plays a significant role.

A case in point is the UK, where several snowy Christmases in relatively recent years, for example around the turn of the millennium and in the early 2010s, have contributed to this increased white Christmas probability.

Also around the Black Sea, there is a notable uptick in the likelihood of a white Christmas in select areas. Yet, these instances might be more of an anomaly rather than an emerging pattern and an uptick in the most recent climatological period does not mean that these places will continue to see upward trends in a further warming climate.

In stark contrast, the far north of Europe and the high Alps show no significant change in snow probability; here, a snowy Christmas Eve remains almost certain. Despite regional warming, the winter temperatures in these areas are still predominantly below freezing, ensuring that precipitation falls (mainly) as snow and existing snow cover stays intact. In some northern regions, like Lapland, the amount of snowfall has even increased (although there is no significant trend in maximum snow depth). This is attributed to milder air carrying more moisture, resulting in heavier snowfall.

We also don’t see clear changes in for example the Benelux region, which makes sense because the probability of a white Christmas Eve was already very low in the past.

Trends in snow probability on Christmas Eve

Whereas the previous map highlighted the difference between two climatological periods, and might be a decent indicator of a trend, this difference in snow probability between two climatological periods is not completely the same as a trend, as these periods can be influenced by yearly weather variations. Therefore, we also computed trend lines in snow probabilities across Europe for each datapoint. This approach offers a more ‘fair’ comparison, though it too has its limitations (which we’ll delve into in the methodology section at the end of this article).

When we look at the snow probability trend from 1970 to 2022 in the figure below, we see that the decrease in white Christmas probability is even more pronounced in many areas. Extending our view back to 1950 intensifies this trend, with positive trends almost completely disappearing. However, there remains a slight positive trend in southern Great Britain. This suggests that while most of Europe is experiencing a decline in the likelihood of a white Christmas, snow on Christmas has indeed become (slightly) more likely in southern Great Britain over the past decades. Again: it is not necessarily likely that this slightly upward trend will continue in a climate that continues to warm.

Snow Cover Probability Trend 1950-2022 on Christmas Eve (climatology 1991-2020) -White Christmas in Europe - Christmas Snow Chance

To conclude: where will it be a white Christmas in Europe?

To conclude, the results discussed in this article offer clear guidance for those seeking a guaranteed white Christmas in Europe. The far northern regions and the highest mountain ranges are your best bets. As a general rule, the further northeast you travel in Europe, the higher your chances of experiencing snow on Christmas Eve. However, it’s important to note that snow cover probabilities on Christmas Eve have been steadily declining in much of Europe over recent decades. There are a few exceptions, such as southern England, where we’ve seen a small uptick in white Christmases in recent decades. In the future, as Europe will continue to warm, the likelihood of a white Christmas is expected to decrease further, making snowy Christmases an increasingly rare phenomenon across most of the continent.

Check the white Christmas probability in US here.

Methods:

For this examination, we utilized the ‘Snow Depth’ variable from the ERA5 dataset, a comprehensive reanalysis dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF). Reanalysis involves combining past observations with modern forecast models to recreate historical weather patterns. This method provides a more complete and consistent picture of the atmosphere over time.

We downloaded this variable for the 24th of December at 18 UTC for all years of interest. The original unit of the data is water equivalent (m). This number was multiplied by 100 (to convert to cm) and consequently multiplied by 10 (assuming a snow water ratio of 10). If the snow depth at the 24th of December, 18 UTC, was at least 1 cm, we classified it as a ‘white Christmas’. Note that in some countries, official definitions of ‘white Christmas’ might differ. For example, in The Netherlands, a snow cover must be present at both the 25th as 26th of November, in order to qualify as a ‘white Christmas’, because these are the dates that Christmas is celebrated in this country.

The trends in each grid cell are determined using a linear fit on the binary snow depth data, representing the presence or absence of snow. While linear fits are generally better suited for continuous data and logistic regression might be more appropriate for binary data, the linear fit method was chosen for its simplicity and computational efficiency. This approach offers a broad view of the snow cover trends, indicating general increases, decreases, or stability over time, though it is less precise in estimating exact probabilities or changes.

Interesting? Share it!

Related Posts

4 thoughts on “Chances of a White Christmas in Europe: Declining Snow Cover Trends on Christmas Eve

  1. Interesting article but I hope nature surprises us and that we get a white Christmas in southern Sweden after all!

Leave a Reply

Your email address will not be published. Required fields are marked *