How WRAL meteorologists use ensemble forecasting to determine the chance of 1" or 3" snow in your town

WRAL has been using ensemble forecasts to put together our snow forecasts behind the scenes for years. Now, WRAL has the exclusive ability to show you that data on TV.

Let’s take this weekend for example.

The image below shows the European model ensemble's chance of 1” or more of snow across our viewing area. Instead of a weather model producing a single forecast, ensemble forecasting produces a wide range of solutions.

Ensemble forecasts achieve this by running the computer models a number of times from slightly different initial conditions. This particular snow example uses 50 different model forecasts and shows us how many model runs out of 50 show 1”+ snow in each city.

The conditions and numbers that go into our weather models are only an estimate of our atmosphere.

The ensembles produce multiple forecasts that help meteorologists better understand the wide range of solutions only a tiny change in the atmosphere can make.

Even though the changes in the initial conditions are very small, ensembles show us that this small difference can create massive differences in outcomes days ahead.

The spaghetti plots, such as the one below, and that you see us use so often during hurricane season, are another way to look at how valuable ensembles forecasts are. Spaghetti plots are made using ensemble forecasts.

Those show how tiny differences in the beginning of a model create large differences in the tracks down the road.

Despite the wide range of solutions they often create, this is an easy way to start seeing trends or “clusters” of possible outcomes.