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WeatherBlog 22 2021/22 | Spring fatigue

Towards the summer

by Lea Hartl 04/20/2022
Despite the relatively cold Easter days, we are taking big steps towards summer. The PowderGuide weather is also approaching the summer break and we will soon discontinue the usual weather service. If it does get wintry again, the WeatherBlog will report on a case-by-case basis.

Current situation and outlook

A high-over-low situation usually ensures relatively friendly but somewhat unsettled weather. High-over-low means that an often self-contained high lies to the north ("over") a low. The whole thing is sometimes also called a Rex block and, like the Omega situation, is a "blocking" weather situation that hinders a zonal westerly drift and likes to stay in place for longer.

So also currently: The constellation "high over Scandinavia, low pressure south of it" will remain with us for the time being. However, the low pressure is shifting back and forth a little. This doesn't look like much on the big weather map, but it certainly has consequences for the weather in the Alpine region. At the moment, there is still a relatively pronounced west-east divide, with cold air in the east and an early summer feeling in the west. This divide will decrease over the next few days and it will gradually become warmer everywhere. The current will turn to more southerly directions and the southern slopes of the Alps will increasingly come under the influence of low pressure. Thursday and Friday are expected to be cloudy, wet and overcast in the south, while it will remain mostly sunny in the north with a light south föhn. The forecast for the weekend looks like a continuation of the unsettled, but not entirely unusable weather. There are no signs of a significant change in the general weather situation. It is likely to remain susceptible to showers, especially in the south, otherwise a sun-cloud mix with moderate temperatures can be expected.

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Blocking layers: status update?

Whether, how and why blocking layers are increasing in frequency or otherwise shifting is a recurring topic of speculation and discussion. Two recent scientific articles break this down in more detail for the European region: This review paper summarizes the current state of knowledge, in case anyone wants to read up. There is still no very clear answer to the question of what climate change is doing to blocking, and the answer varies by region and season. Recent climate model calculations suggest that there will be a spatial shift towards Eurasia, as well as a shift to higher latitudes (i.e. more blocking in the east and north from the Alps). Some models also assume that blocking regions will become larger. The models do not currently see an increase in blocking duration in the future.

This study uses reanalysis data, i.e. a type of weather data from the past, to investigate whether and how the frequency of Omega and High-Over-Low, or combinations thereof, have already changed in Europe in the period 1990-2019. Here, too, the first thing that becomes clear is that it is complicated and there are no simple answers. The frequency per year has not changed significantly, but there has been a relatively significant increase in individual months over the study period, especially in the omega locations. In February and March in particular, the omega locations increased, whereas in December they decreased significantly. Over the year as a whole, these monthly effects more or less balanced each other out.

In climate research, there are often two different sides to a question: "detection" and "attribution". In other words: quantifying changes (detection) and attributing changes to a causal, causal process (attribution). The former is also often much more complex than it might seem. How do you even find out what kind of weather conditions have occurred where over the last 30 or 50 or 100 years? On what data basis? What are the uncertainties? What is a "real" trend and what is just statistical noise? A lot is currently happening with regard to changes in weather patterns, both in terms of detection and attribution, as we are slowly entering an area in which the time series are firstly long enough for climatological evaluations and secondly should already at least partially reflect the suspected changes.

We remain curious, wish you a nice and long late winter and then a successful summer, no matter how the weather turns out!

This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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