What is the difference between the Weather Generator baseline and the baseline used for the probabilistic projections?

The Weather Generator baseline is based on an observed gridded dataset. The probabilistic projections baseline is a modelled baseline.

In detail

The Weather Generator is trained on a 1961–1990 baseline of rainfall and 1961–1995 baseline of other observed variables, gridded to a 5 km resolution, i.e. if there is more than one observing station in the 5 km square then the two stations are averaged, if there is no observing station in a square then data is extrapolated from the neighbouring grid squares.

Although the Weather Generator is trained on an observed climate, the baseline data set that is returned for the Weather Generator is essentially a modelled baseline fitted to 1961–1990 to be inline with the standard baseline used in the project.

The probabilistic projections use a baseline (1961–1990) that is modelled using the Met Office Hadley Centre model. The modelled baseline is then validated against the observed dataset.