Frost during the Ice Saints?

An analysis by GeoSphere Austria for the last few decades shows: The Ice Saints' Days (12 to 15 May) are not a typical time for cold spells that bring frost. Nevertheless, it makes sense not to place or plant sensitive plants outdoors until after the Ice Saints. This is because the likelihood of ground frost decreases significantly over the course of May.

The Ice Saints are on the calendar next week, from 12 to 15 May. They are among the best-known country proverbs and can be found in numerous sayings, mostly in connection with frost. For example: ‘Pankrazi, Servazi, Bonifazi are three frosty bazi. And finally, the cold Sophie is never missing.’ In some regions, Mamertus Day on 11 May is also one of the frost saints' days.

Although it will remain a little too cool for May next week, according to the current forecast, there will only be isolated frost (lowest temperature below 0 degrees) in the inhabited regions of Austria, such as in places in the Waldviertel, Mühlviertel and some Alpine valleys. This means that at least in some regions of Austria there will be very punctual ice saints this year.

But the question is: Are frosty nights typical of the Ice Saints' period or does frost in May have nothing to do with St Pancras, St Servatius and St Boniface?

‘The data from the last 80 years or so for various regions of Austria show that Frost does not occur with above-average frequency on the date of the Ice Saints, from 12 to 15 May,’ says Alexander Orlik, climatologist at GeoSphere Austria, ’nevertheless, it makes sense not to place or plant sensitive plants outside until after the Ice Saints. This is because the risk of ground frost is most frequent in the first third of May, much less frequent in the second third of May - the time of the Ice Saints - and in the last third of May, ground frost is rare to non-existent in the inhabited regions of Austria. Overall, the probability of frost in May has decreased due to global warming in recent decades.’

In the majority of inhabited regions in Austria, ground frost (temperature below 0 degrees, measured five centimetres above the ground) only occurs every few years.

For example, in the recent past (climate period 1991 to 2020), a day with ground frost in the first third of May occurred on average every five years in Vienna and Salzburg, every two to three years in Feldkirch and Klagenfurt, and every one to two years in Innsbruck. In the last third of May, on the other hand, a day with ground frost occurred on average every five years in Klagenfurt and every three to four years in Innsbruck. In Vienna, Salzburg and Feldkirch, the probability of ground frost in the last third of May is almost zero.

In valleys at higher altitudes, ground frost is somewhat more common in May. For example, in Lienz (T, 661 m above sea level) and Irdning (ST, 697 m) in the recent past (climate period 1991 to 2020), there was an average of one to two days with ground frost per year in the first third of May. In the third third of May, on the other hand, there was only one day with ground frost every two to three years.

‘To summarise, it can be said that cold spells are quite normal in May and can occasionally bring frost. But this doesn't happen more frequently during the ice saints‘ days,’ says climatologist Alexander Orlik from GeoSphere Austria, ‘the greatest risk of frost is in the first third of May. The likelihood of frost decreases from the second third of May onwards, i.e. around the time of the ice saints.’

Weather forecast

Translated with DeepL.com (free version)