WeatherBlog 22 2020/21 | April remains wintry

Review of the alert situation

The past weekend was characterized by stormy foehn winds and mild temperatures in the north, while in the south it was cloudy in the traffic jam and there was already some precipitation. The really striking change in the weather then came during Monday with a cold front from the northwest, which gradually worked its way from west to east and initially brought precipitation to the north. The station graphs show how abrupt the changeover was: with the arrival of the front, the wind direction suddenly changed from south (Föhn) to north and the temperature plummeted by over 10°C in just a few hours in some places.

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Weather station on the Schaufeljoch, Stubai Glacier. With the arrival of the cold front, the wind picks up and the temperature drops significantly.

lawis.at

The cold air from the north, which was able to flow in behind the front, made it over the main ridge into the northern Mediterranean region, allowing a small marginal low to develop in the lower layers of the atmosphere in the Gulf of Genoa. This resulted in a northerly or north-easterly wind near the ground. At this time, however, the upper-level flow was still coming from the south, as the upper-level trough was only moving slowly to the east. Due to the different flow direction ("countercurrent system"), there was quite heavy precipitation yesterday (Tuesday), especially in the southern eastern Alps: Warm air (above) pushed over colder air (below). In the western Alps, where the marginal low became less relevant in the lower layers, it was often sunny in the meantime, albeit with cold temperatures thanks to the polar air masses. The complex back and forth of the currents over the Alps in the last few days is explained and animated here. MeteoSwiss has also prepared the whole thing beautifully with various graphics

Sun window on the freshly snow-covered Nordkette

LH

Outlook

High pressure may prevail throughout the Alps today (Wednesday), the further east, the longer clouds and the last showers will persist. However, the main precipitation will be over and the various low pressure centers in the different storeys will move eastwards. What we are left with is relatively cool air and a rather unstable stratification. This means it is likely to remain cool for the time of year up to and including the weekend, with a mixture of sun and cloud and the odd shower here and there.

Long periods of frost in April, as we are currently experiencing, are quite rare. However, there are individual days with frost in April in the Alpine region almost every year. In recent years, late frosts have repeatedly caused damage to wild and cultivated plants, but this is not so much because the April frost was unusual, but because flowering took place unusually early, as there were already very warm periods in February and March.

So: don't ring in the gardening season this weekend and go skiing again instead!