Why are my piano keys sticking?

I live in new mexico, its been in the 90's lately, mid summer, and unseasonably windy and dry. weve been getting pretty much constant 30 to 50 mph wind lately, coupled with three wildfires burning near our location. The humidity reads as 7% today, its been down to 5%. In the past week, at least 6 keys on my yamaha studio piano have started to stick. we just had it tuned and it has been playing fine until all this started. Could low humidity be a cause of this? How can I fix it? Every site ive read said high humidity does this. Please help! Im a musician and i need this piano to be functional.