Currently OWM doesn’t return any values for “Probability of precipitation” . This values aren’t shown in the sensor and weather-entity. See: https://www.home-assistant.io/integrations/openweathermap/
So I don’t know If I have to take my umbrella with me or not 
OpenWeatherMap return theses values with the new One Call Api. See Parameter “daily.pop” https://openweathermap.org/api/one-call-api#parameter
It would be great if this values are added to the OWM-integration.