Are you sure you have an entity weather.openweathermap?
You have configured your sensor with only a Time Pattern trigger which is set to fire at the top of each hour. Any time you make changes to the sensor configuration and reload the template integration, the sensor will be unknown until the start of the next hour.
This is my Open Weatherman setup, and it seems to work fine. The significant difference I see is that I’m getting the daily forecast and not the hourly. The other thing you might need to check is to see if you are still using the old 2.5 API, which is depreciated. You might need to update your OpenWeatherMap account to use the 3.0 API and get a new key.