The attached weather chart and the Winston Salem weather station are what we generally use for weather decisions in outdoor or non-air conditioned physical education classes and during recess. Athletics have different guidelines for determining the safety of athletes in practice and game settings.
In general, on the attached chart:
Green requires no precautions
Yellow requires appropriate clothing for cold weather, close monitoring of activity, and 30 minute time limits
Red is not appropriate for outdoor play/activity at school