DENVER — The National Weather Service says its computer models made it difficult to predict the location and magnitude of heavy rains during Colorado's deadly September storms, but forecasters were still able to give an average of nearly 70 minutes' warning of flash floods.

The agency issued a report Wednesday assessing its performance during the floods, which killed nine people and caused $2 billion in damage.

From 8 to 17 inches of rain fell in seven days along the mountains and foothills.

The report says forecasting models gave varying predictions on the time, location and magnitude of rainfall, making it difficult to provide accurate forecasts.

But the lead time for flash flood warnings averaged 69 minutes, beating the national goal of 58 minutes.

The report also cites problems with slow Internet connections.