At extended range the day-to-day trajectories are affected by substantially larger uncertainty. Therefore, the evolution of the forecast anomalies is represented by the Probability Distribution Function (PDF) based on daily values of individual member projections verifying a given week.
PDFs for the latest extended range forecast. (the diagram is updated every Monday and Thursday). Each panel shows the PDF of the latest forecast valid for four subsequent weeks.
PDFs with verification for the forecast issued 4 weeks earlier. Daily values from the analysis are represented by yellow (first day) to brown(last day of the target period) circles.
Further reading:
Ferranti L, Magnusson L, Vitart F, Richardson DS. How far in advance can we predict changes in large-scale flow leading to severe cold conditions over Europe?
Q J R Meteorol Soc 2018;144:1788–1802. https://doi.org/10.1002/qj.3341