On Saturday it could snow down to low altitudes. The air quality has already improved significantly due to the change in weather.
This photo from April 28, 2017 from St. Gallen proves that the onset of winter can also occur much later in the year than this time.
The magnolias have long since blossomed in Zurich, as have the forsythia and many fruit trees. On Monday the thermometer reached the 20 degree mark in sunshine. On Tuesday it was still 18 degrees Celsius. But now the spring-like weather is over for the time being.
In the middle of the week the air was already getting cooler with the rain. Winter returns on Friday and Saturday – with cold winds and snow showers. The cause of the weather change is a low pressure area that forms over northern Italy on Thursday. On its north-west flank, it sucks in polar air from Scandinavia, which reaches Switzerland via Germany. The winter weather had already arrived in Hamburg on Thursday morning – the city woke up under a thin layer of snow.
According to Meteo Schweiz, there will be a strong breeze on Friday. The snow line, which is initially at 600 to 800 meters, is gradually falling down to the lowlands. During the day the temperature in Zurich drops from 6 to 1 degree. On Saturday the thermometer will not even climb above 2 degrees.
According to the WSL Institute for Snow and Avalanche Research in Davos, there could be 20 to 60 centimeters of fresh snow in the Swiss Alps by Saturday morning. Beginning on Friday, the avalanche danger increases sharply. It can be significant on the northern slopes of the Alps and in parts of Valais (level 3 of 5). Above all, dry avalanches consisting of fresh and snowdrift snow must be expected.
Fruit blossoms could freeze
The forecast models differ a little as to how far down the snow will lie. But at higher altitudes in the canton of Zurich, a thin white blanket must definitely be expected on Saturday, possibly also in the lowlands.
There may even be frost again at night at the weekend, and it is feared that blossoms on fruit trees will freeze to death. According to the weather forecasts, this danger in Switzerland exists primarily on the nights from Saturday to Sunday and from Sunday to Monday. It won’t be milder again until the beginning of next week.
The current onset of winter is not exceptional – neither the date nor its strength. In April last year, the temperature fell twice within a few days from the 20-degree range to wintry values.
Fine dust is passé
As unfortunate as the retreating spring air may be, the onset of winter also has an upside: the air has become cleaner with the influx from the northeast. According to the National Air Pollution Monitoring Network, it still contained an excessive amount of fine dust up until Wednesday. This was evident from the particles with a diameter of up to 10 microns. On Wednesday morning, the 24-hour average concentration of these particles in Basel, Bern and Zurich was temporarily above the limit of 50 micrograms per cubic meter. To protect health, this limit should only be exceeded three times a year.
Part of the particulate matter came from local sources, part from the Sahara. According to Meteo Schweiz, the air turbidity was weaker than during the Sahara dust episode that occurred in mid-March. On the other hand, this time the deeper air layers were more affected. In any case, the recent dusty episode ended on Wednesday due to the onset of cold air.