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The extended range (monthly) forecasts provide a range of possible future weather states in the extended range and bridge .  It bridges the gap between medium-range and seasonal forecasting. 

The extended range forecast

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ensemble:

• is run once daily, base time 00 UTC, producing a 32 day forecast (Day15 to Day46). 
• has horizontal resolution of 36

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• Km and vertical resolution of 137 model levels

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• .  These values are the same as the IFS version before Cy48r1.
• has land-atmosphere and ocean-atmosphere coupling.
• has 100 ensemble members plus an unperturbed ensemble member (CONTROL).

  The ensemble consists of one unperturbed member (the control) and 100 perturbed members that are similar to the control but their initial states and model physics have been perturbed to explore the currently understood range of uncertainty in the observations and the model.  A set of extended range re-forecasts provide a basis for the extended-range model climate (ER-M-Climateclimate).  The extended range forecast suite is not an extension of the medium-range forecasts but is a completely separate system.  

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The medium range and extended range models have the same structure and physics etc. but different spacial (but not vertical) resolutions and differing land-sea masks and orography.  Users should be aware that the output is effectively from different models.  This is especially important when generating a time-series that crosses the boundary between the end of the ENS ensemble 15 day forecast and the start of the extended range.  Users need to develop interpolation procedures that take these changes into account.

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