Modern enterprise data warehouses have complex workloads that are notoriously difficult to manage. One of the key pieces to managing workloads is an estimate of how long a query will take to execute. An accurate estimate of this query execution time is critical to self managing Enterprise Class Data Warehouses.In this paper we study the problem of predicting the execution time of a query on a loaded data warehouse with a dynamically changing workload. We use a machine learning approach that takes the query plan, combines it with the observed load vector of the system and uses the new vector to predict the execution time of the query. The predictions are made as time ranges. We validate our solution using real databases and real workloads. We show experimentally that our machine learning approach works well. This technology is slated for incorporation into a commercial, enterprise class DBMS.