Improve Air Temperature rendering

![before](https://f.cloud.github.com/assets/2202442/1230886/93c44b8c-2813-11e3-909f-24dc4a2b9c9e.jpg)
![after](https://f.cloud.github.com/assets/2202442/1230887/97f94b3a-2813-11e3-84e9-5c652b00d019.jpg)