Looking at a 10-day forecast (from Erfurt), it looks like it's going to cool down and stick around 20 from Thursday (with some rain) until the end of the con. Without trying to curse anything, it looks like the nicest (and warmest) weather will be on Tuesday and Wednesday. Akeela must be working his magic as always.
EDIT: The page I'm looking at is screwy, it says a high on Thursday of 24, but when I clicked for more details, it said a high of 32. So, take all of the above with a grain of salt.