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Remarks on the sub-seasonal range
Sub-seasonal range structure
The sub-seasonal range ensemble is run daily based on 00UTC data. The products cover the period up to Day46 and are derived from a 100 member ensemble with a control and has a resolution of 36km. The sub-seasonal range ENS is independent of the medium range ENS and has it's own control and sub-seasonal range model climate (SUBS-M-Climate).
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Re-forecasts provide an sub-seasonal range climate (SUBS-M-Climate) and associated probability distribution functions (pdfs) for several variables. The latest sub-seasonal range ensemble forecasts and the associated probability density functions can be compared with the SUBS-M-Climate. The differences between the two are used as the basis of model products any model drift is effectively removed.
Combating Model Drift
Drift of model calculations begins to be significant after 10 days of coupled integrations. It displays similar patterns to seasonal forecasting after 6 months of integrations, but with less amplitude.
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The re-forecasts are created twice a week (Mondays and Thursdays) and are ready a week before the real-time forecasting suite starts. Real-time forecasts are calibrated using all the re-forecasts available in a one week window centred on the forecast start day and month.
Fig5.2-1: Example of plumes for Dublin. Extended Range forecast, DT00UTC 1 January 2018. The plumes show increasing spread of forecasted values of 850hPa temperatures and 500hPa geopotential height within the extended range period.
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