It’s mid-October, so it’s back in the air: winter forecast. In recent years cold winters were predicted remarkably often, which subsequently failed to materialize. This does not surprise experts: the winter forecasts were not based anywhere and have virtually no value in the Netherlands, say climate researchers Peter Siegmund and Geert Jan van Oldenborgh of the KNMI in conversation with NU.nl.
“Winter forecasts have virtually no value for the Netherlands. So we don’t make them at KNMI,” said Siegmund and Van Oldenborgh.
Some commercial weather agencies do. Especially in the United Kingdom “the approaching horror winter” is a recurring hype. And Piet Paulusma also makes the news every year with an expectation of the skating opportunities in January and February.
At the KNMI they are certain: you can predict the weather fairly reliably up to a fortnight in advance. The same models also produce a monthly forecast, but it is broadly based and unsuitable for public communication.
“With summer showers you sometimes do not know an hour in advance where they will fall, at most that they will form somewhere.”
Peter Siegmund, KNMI
It’s a different story in the tropics. There the weather is not only less erratic than ours, but also more predictable over a period of months. This is due to the influence of fluctuations in tropical ocean temperatures, so that Indonesia and Peru, for example, sometimes know months in advance whether they can expect flooding or drought.
In Australia and North America, tropical ocean temperatures also have an influence, but in Europe actually not, the researchers say. This also applies to fluctuations in water temperatures in the Atlantic Ocean.
A cold or warm North Sea: you won’t notice it in Maastricht
The temperature in the North Sea does make a difference. If it deviates, it will affect our weather in the autumn and spring. However, because the North Sea is relatively shallow, this effect usually fades away after a month. “And it is only noticeable in the coastal areas. In Maastricht you can no longer base a monthly forecast on it,” says Van Oldenborgh.
Can we not predict our winters at all? Well, it could be worse, says Siegmund: the Dutch summer. “With summer showers you sometimes do not know an hour in advance where they will fall, at most that they will form somewhere.”
“How much gas is needed for heating, how much road salt for the roads? Will farmers have to deal with flooded fields? Will there be an Elfstedentocht? We want to know, but are largely in the dark. ”
The fact that the Dutch winter weather is more predictable over a period of fourteen days is due to the influence of ‘slow vortices’ in air currents at high altitude in the atmosphere. These determine whether cold air lingers around the North Pole or makes forays into lower latitudes and can be predicted up to about a month in advance.
Reliable winter forecasts would be valuable
There is also more variation in winter: the difference between a cold and mild winter is much greater than between a hot and cool summer. That wide variation would make reliable winter forecasts very valuable.
How much gas is needed for heating, how much road salt for the roads? Will farmers have to deal with flooded fields? Will there be an Elfstedentocht? We would like to know, but are largely in the dark.
Things may be different one day: research is being done to predict cold spells longer in advance. “There are indications from weather models that some winter air pressure patterns are predictable for longer,” says Van Oldenborgh. “It’s unclear whether that will lead to meaningful winter forecasts. But it’s an interesting new scientific development.”
Siberian autumn snow and weak sun do not bring ice skating
Other connections do not appear to be valid from further research. For example, it was thought that winter cold depended on the amount of autumn snow in Siberia. That has been debunked. Variations in the strength of the sun would also determine our winter weather.
“At high altitudes in the atmosphere, the eleven-year solar cycle produces subtle temperature differences,” says Siegmund. “But you don’t see it in our weather.”
What is striking about the winter forecasts of commercial weather agencies is that they almost always predict a cold winter. “Every year a horror winter is predicted in October. That has indeed turned out beautifully for the past seven or eight years,” jokes Van Oldenborgh.
If there is one thing predictable about the Dutch winters, it is that they will become milder and rainier. Perhaps that’s why we love to read about thick packs of snow and endless ice skating.