The D1M & D1S solar powered weather stations heat up in direct sunlight giving an incorrectly high-temperature reading. Early results from testing an Acurite solar radiation shield are very good.
The shield is available from several online vendors although it appears to be out of stock until August 14, 2017. Check around for a good price as the same item sells for $10 to $60 from different vendors.
I inserted a D1S shield-type station into the Acurite product and hot-melt glued the solar panel to the side of the solar shield. The shield comes apart by carefully prying small plastic tabs between each layer. This makes it easy to run wires into the shield.
On sunny days, the unshielded sensor heats up by more than 20ºC (36ºF).
Since product availablility is problematic, I am going to look into the possibility of building a DIY solar shield with dollar store components.