Hi Marcel,
So you compare forecast temperature with your observation, but maybe you don’t use the best weather model for your location.
To know which is the best one, select Reported temperature in low right corner of your screen.
Then click on a weather station (the small bubbles) near your location. You get a comparison of forecast temperature with the observation at this weather station during last days. At bottom of the panel select the model which gives the best matching.
Here we see that the ECMWF model does not give so good temperature forecasts:

Selecting Meteoblue you see that the curves match very well.
So for temperature it could be a solution to choose Meteoblue in the Meteogram for temperature forecast.

Try AROME too. In mountains high resolution models give better results.

This is due to the accuracy and spatial resolution of each model, as well as to the difficulty of computing a good forecast over a region like yours, surrounded by mountains, valleys and a big lake in the middle...

Did you tried to compare the "real" temperature with the most local and trusted forecast office (e.g. meteoswiss)?