With severe asthma should you and what kind of mask to wear outside for each weather season and is it nessasay ?

Ask your doc: The preventive practices of any patient differ with their specific triggers. Weather changes may not be a factor for some while being major for others. The type & quality of any mask would also depend on what you are trying to avoid, be it particles, germs, smoke, etc. I would consult with your treating doc to see what would be right for your specific needs.