In Switzerland in the second half of June the weather is mostly warm and dry, but relative humidity can be rather high and sometimes it is even sticky in the afternoon. In high altitudes temperatures are significantly lower than in lower areas. Under sunny conditions local valley wind systems develop, causing fairly steady, but brisk uphill breezes. There is a moderate risk for isolated showers or thunderstorms in particular after midday. When the first rain drops meet the dust on the roads after a dry period, the surface could become slippery.
If southerly winds carry moist and instable Mediterranean air to the southern slopes of the alps, heavy precipitation and frequent thunderstorms are likely.
Sometimes, the area is under influence of maritime polar air. In such a case, the weather is wet and rather cool. Foggy patches can reduce view significantly. In exceptional circumstances, even snow fall is possible at altitudes above 1800 msl.