You're already taking just about everything possible for allergy and asthma. I'm glad to hear about the rain. That will make your life a lot easier. Take your inhaler, and keep it handy. Didn't you tell me once that you use Albuterol? Best keep it somewhere you can find it in case you need a breathing treatment. I'm sure you can find an outlet somewhere.
If your weather's overcast I don't anticipate any major problems. I really think it's going to be okay. However, if you really start feeling bad just turn your fanny around and go home. Have fun!