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Extended-Range Forecast

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

The extended range forecast suite runs daily from base times 00 UTC out to day 46.  It has horizontal resolution of 36 km, 137 model levels in the vertical and has land-atmosphere and ocean-atmosphere coupling.   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 ER-M-Climate.  The extended range forecast suite is not an extension of the medium-range forecasts but is a completely separate system.  

The extended-range forecast provides an overview of the atmospheric evolution for the 32-day period (Day15 to Day46).  Standard output products focus mainly on the week-to-week changes in the weather.  The chart products generally are presented in terms of anomalies relative to the extended-range model climate (ER-M-climate) and are mainly shown as 7-day means for calendar weeks Monday to Sunday.  From these one can infer whether conditions (e.g. temperature, rainfall, etc.) are likely to deviate from the average for a location and time of year, and whether such an anomaly could be extreme.

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