Europe braves a cold and wet spring – here's the summer outlook

Spring has not yet arrived in large parts of Western Europe. It was particularly miserable in Great Britain, where this was recorded Coldest April in a century and experienced an unusual wet May.

It has been raining for weeks in the Netherlands, where I live. We also had the coldest April in decades, inclusive more snow than every year since 1977. Most of Western Europe has a cold streak with the sun hidden behind storm clouds and Hailstorms.

So is it getting better or is summer 2021 doomed?

The best models we have can only accurately predict the weather up to two weeks in advance. The further we go, the less reliable these forecasts become and the more uncertain these forecasts become. That is, the European Center for Medium-Range Weather Forecasts makes weather forecasts that last longer than half a year.

Surely we can’t trust the weather forecast for six months, can we?

This is not entirely true – while these predictions shouldn’t be used as a basis for your biking and hiking adventures, we can definitely use them for long-term planning. For example, water managers can plan their operations based on long-term estimates of precipitation and temperature to anticipate upcoming droughts, and farmers can adjust their crops to the most likely summer conditions.

These seasonal forecasts can tell us whether a season will be wet, dry or “normal” and warm or cold compared to normal conditions. Scientists are pretty good at predicting these seasonal anomalies, but the further in time we go, the better It becomes more unpredictable. Seasonal forecasts cannot predict the rain on a given day about three months in advance.

Unfortunately, Western Europe is one of the hardest places in the world to predict long-term weather. This is because the weather in the region is largely determined by irregular air currents across the Atlantic and does not show any long-term persistent patterns. Therefore, Europe is more difficult to predict than regions like California or South America, where the weather is partly due to anomalies in the more stable weather patterns of the Pacific Ocean.

To determine the “ability” or usefulness of such a seasonal weather model, scientists look at historical forecasts and compare them with current observations. Just like I could predict the weather for next week, and next week we’ll see if I was wrong or right. If we do this over an extended period of time, we can see if these models work and if they have predictive capabilities.

In this way, scientists have shown that seasonal weather models are bad Predict rainWhile the temperature forecasts provide more useful information and displays more predictive ability. This means that in most cases the models correctly predict summer temperatures.

So now the big question, what does that mean for summer 2021?

The models predict normal to warm temperatures and that it will be a little drier than usual. Southern Europe in particular has a high likelihood of above average temperatures (i.e. above the long-term average from 1990 to 2020), while the UK and Northern Europe should have normal temperatures but drier conditions.

The European Center for Medium-Range Weather Forecasts predicts that July 2021 will be warmer than usual across Europe (but not on the southern tip of Portugal). ECMWF, CC BY-ND

If the summer is warmer than normal, it is not really due to the cold, wet spring as the weather conditions do not last long enough. Instead, the predicted warm weather is part of a major trend of warmer summers and more droughts thanks to climate change.

As the world warms up, on average, most forecasts will predict normal to warm summers. If you need to make an educated guess, this is your best bet.

Seasonal forecasts definitely add value if you know how to use them. But we need to be aware of their limits and view them as a general prediction or sense of direction. We expect the summer to be normal to warm, but this is only an increased chance given the information we now have based on current conditions and forecasts – any forecast can still be wrong, of course. After all, often nothing is as unpredictable as the weather.

Niko Wanders, Assistant Professor, Hydrological Extremes, Utrecht University

This article is republished by The conversation under a Creative Commons license. read this original article.

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