Solar Eclipse

Clouds are one of the most difficult weather parameters to forecast, even just a few days ahead of time, let alone more than 10 days out.

It’s not just large storm systems that produce extensive cloud cover. Those clouds are relatively easy to forecast, especially within a few days. Smaller, weaker disturbances in the atmosphere can generate clouds as well, even when they don’t have enough moisture to make precipitation. Meanwhile, skies can transition from completely cloudy to totally clear within just 50 miles or so of a weather front, while model forecasts for the location of a front can be off by twice that much a day or two beforehand.

The challenge is that cloud cover often depends on processes happening at very small scales in the atmosphere — small enough that models don’t have enough detailed data to accurately resolve them.