What are ensemble forecasts and how do forecasters use them?
Ensemble forecasting is when meteorologists run computer models multiple times at the same time, obtaining different results by slightly changing the initial conditions or observations that the model begins with. (Other ways to create an ensemble is to use different ways of calculating the physics that the model uses, or even using a few different models.) One reason this is done is because the sensors that obtain the initial measurements have a certain amount of uncertainty associated with them, so the ensemble creates a range of plausible solutions for the actual current state of the atmosphere. A meteorologist can then compare all the different model runs to help determine what the range of possible forecasts is, as well as help determine how confident they are about certain parts of the forecast. For example, part of an AFD might read, “Ensembles are in good agreement for high pressure persisting across the area for days 4 through 7…so confidence is high that our hot and dry patt
