The European Centre for Medium-Range Weather Forecasts (ECMWF) provides Subseasonal-to-Seasonal (S2S) forecasts, which are crucial for understanding weather patterns on timescales ranging from 2 weeks to 2 months. These forecasts are essential for applications in drought prediction, agriculture, hydrology, and climate research.
ECMWF S2S Ensemble Members
The ECMWF S2S system utilizes an 11-member ensemble for its reforecasts (hindcasts). Each member represents a slightly different initial condition to account for uncertainties in the atmosphere, providing a probabilistic range of possible future states.
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Reforecasts: 11-member ensemble, initialized on the same day and month as the real-time forecast, covering the past 20 years.
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Real-time forecasts: Typically consist of a larger ensemble (e.g., 51 members) to provide a comprehensive range of possible outcomes.
These ensemble forecasts are produced twice weekly, on Mondays and Thursdays, and extend up to 46 days ahead.
Glossary of Key Terms
S2S (Subseasonal-to-Seasonal Prediction)
Forecasts that bridge the gap between short-term weather forecasts and long-term climate predictions, focusing on the 2-week to 2-month timescale.
Ensemble Forecast
A set of multiple forecasts generated by running a numerical weather prediction model multiple times with slightly varying initial conditions to capture the range of possible future states.
Reforecast (Hindcast)
A retrospective forecast run using historical data to assess the model’s performance and correct systematic biases.
Control Forecast (cf)
An unperturbed forecast run using the best estimate of the initial conditions, serving as a reference for the ensemble.
Perturbed Forecast (pf)
Forecasts generated by introducing small perturbations to the initial conditions to account for uncertainty and variability.
MARS (Meteorological Archival and Retrieval System)
ECMWF’s data archive system that stores and provides access to historical and real-time forecast data.
GRIB (GRIdded Binary)
A concise data format commonly used in meteorology to store historical and forecast weather data.
ERA5
The fifth generation ECMWF atmospheric reanalysis of the global climate, providing hourly data on many atmospheric, land-surface, and sea-state parameters.
Accessing ECMWF S2S Data
ECMWF’s S2S data can be accessed through the ECMWF Public Datasets portal. Users can retrieve both real-time forecasts and reforecasts in GRIB format. Access may require registration and adherence to ECMWF’s data usage policies
Downloading Data for 11 Ensemble Members
To download ECMWF S2S reforecast data for the 11 ensemble members:
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Register: Create an account on the ECMWF website.
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Access the S2S Dataset: Navigate to the S2S data portal.
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Select Parameters:
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Origin: ECMWF
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System: Choose the desired forecasting system
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Type: Reforecast
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Date Range: Specify the period of interest
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Ensemble Members: Select members 0 to 10 (total of 11 members)
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Variables: Choose the meteorological variables needed (e.g., temperature, precipitation)
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Download: Submit the request and download the data in GRIB format.
Applications in Research and Practice
ECMWF’s S2S forecasts are invaluable for:
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Drought Prediction: Assessing the likelihood of drought conditions weeks in advance.
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Agricultural Planning: Informing planting and harvesting decisions based on expected weather patterns.
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Water Resource Management: Anticipating water availability for reservoirs and irrigation.
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Disaster Preparedness: Preparing for extreme weather events such as heatwaves or heavy rainfall.