The devil’s in the detail – Medium range forecasts for the public

Oral Presentation

Weather forecasts beyond 7-days are available to the public from many providers. The challenge at this forecast range is to provide a suitable level of detail relative to the skill of the underlying numerical weather prediction models and considering the issue of fundamental predictability. Too specific and the forecast will change frequently and significantly in many synoptic situations from forecast run to run, undermining user confidence. Insufficiently detailed and the forecast provides little value to the user beyond a simple climatology. There is strong evidence that probabilistic forecasts derived from ensembles, ideally enhanced by calibration, can offer significantly improved forecast skill. The IMPROVER system developed by the Met Office produces such forecasts. However, the challenge of presenting the forecasts in a suitable form for the medium range remains. The Met Office is preparing to extend the forecast range of its public offering. This talk will cover some of the diagnostics that are being constructed to provide the public with a picture of the likely weather in week 2 forecasts. The value of aggregation over spatial and temporal dimensions in reducing uncertainty and changeability will be discussed, as will the choice of diagnostics to include and omit from our initial week 2 forecasts.