When I came north to perform at either Virginia, Garden State, Buckeye fests it was always early spring or late fall. It was always cold and I ALWAYS had harp trouble (especially the chromos). They always had to be warmed. When I lived in Pgh, same thing during 5 months of the year.
This is why Robert Bonfiglio warms his harps with a small electric blanket or heating pad before he performs. You want the reeds to be as warm as your breath to prevent condensation.
If you perform with a tube amp, laying the harps on top of the amp will probably do the job.
Thanks, Richard Hunter hunterharp.com latest mp3s always at http://broadjam.com/rhunter