The marked peak seen in the monthly values for Summer 1998 could explain the levelling off of the yearly values since June 1999. However, the overall trend shows a gradual improvement with time. CBS time series data Figure 4. As Figure 4, but 12-month means. Figures 4 and 5 show r.m.s errors of forecast values versus radiosonde measurements for temperature at 250 hPa.
Recent improvements are evident in the UK results compared to the other centres.