There is a “native” OWM Binding available now: OpenWeatherMap - Bindings | openHAB
It works very well! (but you need OH 2.4.0 M5+)
Thread here: Announcing OpenWeatherMap binding for Eclipse SmartHome / openHAB
I decommissioned my old weather1 binding (using Wunderground) recently also (I was getting more frequent errors) and I am using OWM now.