The weather in Gimmelwald can be extremely different. As Gimmelwald is located in the heart of the alps and on 1'400 meters over sea you have to take in consideration that weather might change very quikly and dramatically. Keep in mind that it doesn't get all too hot in very high altitudes, even in July and August (especially in the night). Snow and blizzards are always a possibility in higher altitues, so keep an eye on the weather forecast. It is best to bring along all sort of cloth the whole year round. Don't forget some good hiking boots.
Many tourists look up the weather for the Jungfraujoch and assume, that the weather is the same for Gimmelwald! Please bear in mind, that there are 2000 meter hight difference and unsurprisingly the weather will always be very much colder on the Jungfraujoch than in Gimmelwald!Further information about the temperature and the climate in Gimmelwald (The situation is about the same as for Mürren):
Current weather situation