Page History
...
Fig7.2.2: An example of a forecast exhibiting jumpiness in the form of a major flip-flop. On the diagram the y-axis is for forecast 2m temperatures, the x-axis shows the data time of the ensemble forecast. The plotted values are for the forecast temperature at Paris verifying at 00Z 8 Dec 2016. Forecast ensemble results are shown by box and whisker plots (described in Meteogram section), forecast ensemble mean values shown by black dots (red dots show values from the now obsolete HRES the HRES). Initially Day15 to Day11 forecasts were around 5°C or 6°C although with a broad range of up to ±8 to 10°C. From 12UTC 27 Nov (Day10½) the forecast temperatures jumped to much colder values round -2°C with a relatively small spread of ±3 or4°C. From 12UTC 30 Nov (Day7½) the forecast temperature rose suddenly back to around +6°C with a broader spread of ±8 to 10°C. From 12UTC 3 Dec (Day4½) the forecast temperatures reverted to around +4°C with range of ±2 or 3C. It should be remembered in general each ensemble solution should be viewed as one possible solution that is a member of a greater ensemble of the latest and recent solutions, although the later solutions do have the benefit of the most up to date data.
...
- at short lead-times a small but significant proportion appear better (~15% at Day2),
- at longer lead-times a larger a larger proportion appear better (~40% at Day6). (Fig7.2.4).
Persson and Strauss (1995), Zsótér et al. (2009) found:
...
...