Winter 17-18 was one of the best winters in terms of snowfall in Switzerland. There was clearly more snow than usual. Winter 17-18 is in the top 5 of the snowiest winters of the past 20 years. The following chart shows the winter of 17-18 (the black line). The gray line represents the long-term average. The winter of 17-18 is clearly above the long-term average. Especially January contributed a lot and avalanche danger HIGH (4) or even EXTREME (5) were quite normal. The situation in January had a great resemblance to the avalanche winter of 1999. Luckily, there were no big catasthropical accidents this time.
There was still a lot of snow coming down in May and June in 2017, but May and June were unprecedentedly dry in 2018. The snow disappeared at more and more monitoring stations over 2000 meters from June and all the measuring stations in Switzerland are snowless at the end of July. And that after a very snowy winter. You can see how the snow slowly disappears below. It is going fast in June. The winter of 2016-2017 started late but had a nice peak when most people were already enjoying spring. Season 2017-2018 started early and lots of snow came down, but it ended with some very dry months.
The cause of the rapid disappearance of the snow cover has two reasons. First of all, it was very dry and also very hot during the second quarter of 2018. There was quite a lot of snow (the snow cover was thicker than normal) in the west of Switzerland in the middle of May. You can see that the storms from northwest and southwest brought a lot of snow to the western Alps on the image below. The snow cover over there was pretty good for a long time.
The winter was snowy, the second quarter was really dry. They're measuring the rainfall in Switzerland since 1864. The period April-July 2018 is in the top 5. With a 4th place it hasn't been that dry since 1911. And without snow, a snow cover shrinks quickly. Where storms usually still bring some extra snow in the spring and early summer, there was no significant precipitation this time.
Even more striking is the heat. It hasn't been that warm in the periode April-July since 1864. The temperature in this period was almost 2 degrees celcius above the average of the past year and no less than 3.5 degrees celcius above the average from 1960 to 1990. Drought in combination with extreme temperatures caused the thick pack of snow to disappear quickly.