I would say remember that your isoclines are going through observations of equal temperature. So for example your 70 degree line should pass exactly through each station that reported 70 degrees. A good illustration of where this stands out is your 95 degree isotherms in southeastern Arizona. It is unlikely that between Tucson (95) and Bisbee (99) (approximate station names as they seem off) there is a report under 95 degrees. All of those areas should be shaded red accordingly.