Night frost in September, does it affect the weather?

The 2022 frost season has started. The 1st frost of the autumn was measured on September 20, 2022 in Groningen and Overijssel. Is that early or late in the year? What does this ground frost mean for the remaining winter months? And what do night and ground frost actually mean? We explain.

What are night frost and ground frost?

Meteorologists often use the terms night frost, ground frost and ground frost interchangeably. This is the case when the temperature at night about 10 centimeters above the earth’s surface – at clump height – drops below 0 degrees Celsius. On September 20, 2022, this will be the case at measuring points Eelde (Groningen) and Twenthe airport (Overijssel), while the thermometer in Zeeland shows more than 9 degrees.

These large nighttime temperature differences can be explained, however, because the sea is warmer than the land at night. As a result, night frost occurs earlier in the interior than on the coast. But very local differences are also possible in the interior. At nose height (about 1.5 meters above the ground) it can sometimes be 5 degrees warmer at night than at clog height.

Also read: Tip 7: night frost

Is it normal to have night frost at the end of September?

It’s a bit on the early side, but not unusual indeed. The first local night frost of autumn occurs on average around September 28. Since 2018, September has always been the month of the 1st frost. The most notable outlier comes from 2014, with November 5 as a very late starting point. But otherwise the night frost follows a regular pattern.

What does this night frost mean for the rest of the season?

Will the winter of 2022/2023 be a severe one or a mild one? That is unpredictable based on the 1st frost. An accurate weather forecast is only possible for a period of 2 to 3 weeks, the KNMI explains. In addition, the winter does not start 3 weeks after the 1st night frost measurement in September. There is therefore no correlation between the 1st night frost and the course of the following winter months.

Also read: What is the difference between a meteorological and astronomical season?

Night frost during Ice Saints?

Over the decades, the night frost period has become shorter and shorter. In the 21st century, it starts later in the fall and ends earlier in the spring. This has consequences for agriculture, because (vegetable garden) crops can go outside earlier in the spring. Then watch out for frost damage, because the night frost season can always have unexpectedly late shoots at the end of May. Every year between 11 and 14 May is the period of Ice Saints, but with a bit of bad luck, night frost can sometimes occur afterwards.

(Source: Weerplaza, KNMI, Meteocentrum, Encyclo. Photo: Shutterstock)

The article is in Dutch

Tags: Night frost September affect weather

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