Page History

...

The control member of the medium range ensemble has the same horizontal and vertical resolutions as the now discontinued HRES.  This does not mean that it may be used simply as a substitute for HRES working as a deterministic model yielding deterministic results.  As a forecasting aid it is not a direct substitute for HRES.

There are 50 other equally valid members of the ensemble.  All are equally valid.  There is no reason to select the results from the unperturbed control member rather than any of the others.   And any member viewed in isolation cannot provide any estimate of forecast uncertainty or confidence.   

...

Generally, whether the ensemble spread is small or large, the EM (or median if applicable) will, beyond the short range, exhibit higher accuracy than the ensemble control (CTRL).  This is particularly true for parameters, such as mean sea level pressure (MSLP) and temperature.  However, with increasing spread amongst ENS ensemble members, it becomes more appropriate to couch the forecast information in the form of probabilities rather than as predicted values  - this is particularly true for parameters such as precipitation and cloud amounts.  The EM ensemble mean also displays a higher degree of day-to-day consistency.  Jumpiness in the ensemble mean is also markedly less, on average, than seen in the ensemble control, particularly when examining forecasts beyond about Day3. 

...