This is a Stevenson screen like cap for a thermometer inside a 6 mm carbon rod (as used for kites). The thermoelement is 5 cm from the top end of the rod so the screens can make nice shade on it. 5 lower and one upper part fit nice on 10 cm of the rod.
OpenScad files included in case someone wants to modify anything.
I printed in white PLA and we will see how well it copes with the weather.
Update Januray 2016: After two years in middle european outdoor conditions with lots of sun, rain, snow and temperatures between -15 and +35 °C, I would rate PLA very very weather resistant. Except from getting slightly dirty the material does not show any degradation or brittleness or whatever. I would not recommend black anyway because it just gets too hot in direct sunlight and deforms (as I have noticed with another part).
I however noticed that (my) white PLA is quite transparent for infrared light causing the temperature sensor to "see" something of the direct sunlight and hence showing slightly elevated temperatures as soon as the sun comes through on bright but cloudy days.
So, I exchanged the parts with new ones printed in silver and this seems lightly better although not perfect. Again, I am curious if silver PLA is as resistant as the white one.