Systems and methods for modeling the behavior of an enclosure for use by a control system of an HVAC system are described. A model for the enclosure that describes the behavior of the enclosure for use by the control system is updated based on a weather forecast data. The weather forecast data can include predictions more than 24 hours in the future, and can include predictions such as temperature, humidity and/or dew point, solar output, precipitation. The model for the enclosure can also be updated based on additional information and data such as historical weather data such as temperature, humidity, wind, solar output and precipitation, occupancy data, such as predicted and/or detected occupancy data, calendar data, and data from the one or more weather condition sensors that sense current parameters such as temperature, humidity, wind, precipitation, and/or solar output. The model for the enclosure can be updated based also on an enclosure model stored in a database, and/or on enclosure information from a user. The model can be updated based on active testing of the enclosure which can be performed automatically or in response to user input. The testing can include heating and/or cooling the enclosure at times when the enclosure is not likely to be occupied.