Page History

...

The typical predictability is currently approximately twice the timescale, but might ultimately be three times the timescale.  Small baroclinic systems or fronts are currently well forecast to around Day2, cyclonic systems to around Day4 and the long planetary waves defining weather regimes to around Day8.  As models improve over time these limits are expected to advance further ahead of the data time.  Features that are coupled to the orography (e.g. lee-troughs), or to the underlying surface (e.g. heat lows), are rather less consistently well forecast.  The predictable scales also show the largest consistency from one run to the next.  Fig4 Fig4.1.3 shows 1000hPa forecasts from six sequential runs of HRES verifying at the same time. 

...

The ensemble assesses the forecasts in a consistent and optimal way as its flow dependency serves as a superior dynamic filter.   It gives the probability of an outcome (in this case strength of wind) rather than relying on an individual solution.

 The T+12 h ensemble forecast is used here as an analysis proxy for the verification of the above forecasts (see Fig4.1.6).

...

It can be seen from the above that some of the HRES medium-range forecasts in Fig4.1.3 (T+96hr, T+108hr and perhaps T+144hr) were quite good with respect to strong winds over Britain and Ireland but at the time the ENS indicated that gale force winds were not certain. 

...