Finally, the sun - the onset of the summer heat?  Peter Sigmund of the National Institute of Islamic Institutions (KNMI) has not yet seen this happen

Finally, the sun – the onset of the summer heat? Peter Sigmund of the National Institute of Islamic Institutions (KNMI) has not yet seen this happen

The average temperature was eight degrees Celsius, the coldest spring since 2013, but almost over. The weather summer starts on Tuesday, and the improved weather this weekend is a prelude to that. At least, that predicts Weather online. The institute reported this week that since 1901, only one in six cold springs has followed a cold summer. The last time this happened was in 1987.

A month ago, Weeronline was a little more optimistic. Promise 2021 Wonderful summer : Sometimes it’s cold and damp, but also a lot of heat waves and tropical days. According to the spokesperson, the “broad trend” is causing temperatures to rise in southern and central Europe. “Once the winds blow in the right direction, the mercury can rapidly rise above thirty degrees here.”

Peter Sigmund of the National Institute of Islamic Institutions (KNMI) has not yet seen this happen. He does not see any relationship in the statistics of the last century between spring and summer temperatures. And yes, according to the Europeans Weather computer There is a good chance of a warm summer in southern Europe. But: “They present these seasonal forecasts to the whole world. They are of little value to Europe. KNMI used to work with them in the past, but abandoned them because expectations were often met as they were not.”

He says seasons can’t be expected with us. “We cannot look that far. You can say at most that this wet spring will reduce the risk of heat waves. The evaporation of all that water is consuming a lot of the sun’s heat.”

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This weekend: sun and terrace.ANP photo

Increased temperatures and increased evaporation

Dutch summer is not what it used to be. The average values ​​for the past 30 years are the new normal and have changed significantly compared to the previous period. For example, in a normal summer in De Bilt, the temperature is now 17.5 degrees, compared to 16.2 degrees in the years between 1961 and 1990.

Extremism has increased in particular, although heat waves in recent years have still been exceptional. The hottest day of summer is now an average of 25.5 degrees (it was 23.6 degrees). The number of summer days increased from 15 to 22; Even the number of tropical days has doubled.

There are also significantly more days with heavy rains. You won’t say it after this spring, but the trend is that the rainfall deficit is increasing. Sigmund: “This is mainly due to increased evaporation. With each degree of heating, there is 2% more evaporation. The sun shines more often, and there have been fewer clouds in spring and summer in recent decades.”

But these are averages. The weather can only be partially predicted. “We can look ahead for two weeks. We can do it better and better, but then it will also stop. The chaotic nature of the weather draws a key boundary there.”

not exactly. In the tropics, the warm ocean has such a large influence that meteorologists dare to look a little further. Then you can say: The North Sea has barely warmed up due to the cold spring. But what if that gives a cool start to the summer? Poor connection. ”

Weather columns from KNMI

In the future, it may be possible to predict areas of high pressure for a longer period in advance. Much research is being done on this topic. But this pays off especially in the winter. “Then we see it getting better again. If depression develops in Canada, you know when it will be here. In January we saw how the stratosphere was getting warm and we can actually expect the cold wave in February.”

But the summer is still tough. Then the weather is determined locally to a greater degree. Summer rainfall can be very localized and lower the temperature. ”

If you’re looking for something to stick with, you can call KNMI’s so-called weather columns (ref Hon site Scrolling under “Outlook”). In it, the prediction was repeated fifty times. “If the lines remain close, we are sure we will do. But the feather does not look further than two weeks either.”

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KNMI at the start of the year saw the frost week approaching February.

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