What is the Ultimate Limit of Weather Predictability?

Fuqing Zhang
Penn State
  9 Mar, Noon, in 2155

Through extremely high-resolution global ensemble experiments with state-of-the-science global numerical weather prediction models from ECMWF and US NOAA, this study investigates the ultimate predictability limit of day-to-day weather phenomena such as midlatitude winter storms and summer monsoonal rainstorms. Results suggest such a limit may indeed exist that is intrinsic to the underlying dynamical system and instabilities even if the forecast model and the initial conditions are nearly perfect. Currently, the practical predictability limit of midlatitude instantaneous weather is around 10 days; reducing initial-condition error by an order of magnitude will extend the deterministic forecast lead times of day-to-day weather by up to 3-5 days, with much shorter room for improving prediction of small-scale severe weather phenomena like thunderstorms. Achieving this additional predictability limit can have enormous socioeconomic benefits but requires coordinated efforts by the entire community to design better numerical weather models, to improve observations, and to make better use of observations with advanced data assimilation and computing techniques. In essence, predictability of daily weather may be intrinsically limited to about 2 weeks but can be extended by as much as 3-5 days beyond the current-day limit.