forecastting on supercomputers vs. desktops

Supercomputers are required (and used as you can see from the list above) to run _global_ weather models. Some smaller weather companies run so called mesoscale models -which do not require supercomputers- but are driven by data from the global models. Those mesoscale models are run to get a better regional forecasts.

With climate models it is a bit different.There are global models that you can actually run on a desktop, but they have only a very coarse resolution and a comparetively "simple" formulation of the climate system. To run state-of-the-art models you will definitively need a supercomputer.