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Fig8.2.7-6: Predictability distribution on NAO-BLO diagram.  Ensemble variance colour coded as the scale.  Ensemble variance (spread) is indicative of predictability.  Thus NAO– has relatively high predictability (probably because it tends to be more persistent than other regimes), BLO+ has relatively lower predictability.  The NAO–BLO space explains about 30% of the daily winter variability over Europe.

Transitions between circulation type or regimes

A study using available extended range re-forecasts (12 years of re-forecasts) gives an indication of the ability of the forecasts to capture similar transitions that occurred during the six-day period preceding various selected forecast lead times (Day11, Day16, Day21, Day 31).  The results are shown in Fig8.2.7-7.

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The model statistics and relative frequencies, at all forecast ranges, compare well with those from the analysis, indicating that the IFS is well able to simulate transitions, and suggesting that model bias in this context is not a major problem.

Example of circulation pattern and anomaly charts.

Fig8.2.7-8: Forecast mean sea level pressure mean anomaly verifying Day7-14 (23-30 Oct 2023).  The anomaly of surface pressure from ER-M-climate is:

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