Hi everybody!

Last weekend I went to collect data from my logger. Winter has definitely gone: Sämtisersee had it's last frost on May 20 with -0.8 °C and Hintergrappelen on June 9 with -1.4 °C (plus an impressive -4.5 °C on the night before).

Exceptional in the other direction was the night from June 22 to June 23. This was the warmest night in eastern Switzerland since the beginning of automatic measurements in 1981. The highest minimum has been recorded at the border of Lake Constance: A minimum of 25.2 °C has been measured, the old record was 20.9 °C. I assume that highest night temperatures in Italy are higher than here in Switzerland on the northside of the Alps, but nightely minima of >25 °C probably also not bad for Italy...

Beside the very warm airmass the overcast sky was the main reason for the warm night. What happened in the (not so frosty) frost hollow in the Alpstein region?

The blue line shows Hintergräppelen, the yellow line Sämtisersee lower station and the orange line Sämtisersee upper station.

It was really surprising for me to see that at Lake Sämtis a tropical night (temperature > 20 °C between 18 UTC and 6 UTC) was only just missed. Hintergräppelen dropped > 7 K to ~15 °C due to a clear spell.

Some additional details are presented under http://kaltluftseen.ch/2017/07/19/tr...napp-verfehlt/

Best regards, Stephan