The temperature sensor needs a radiation shield to protect it from direct sunlight, but still allow air circulation to get an accurate air temperature measurement. Here is an example
of one made with sheet metal. Another method involves several plastic dishes for a small flower pot. They are oriented upside down, all but the top one have most of the bottom cut out, and they have spacers between them. IIRC they should be painted white.
Look at some of the commercial weather stations for ideas, then rummage around the kitchen or local discount store for parts.