The Sub-seasonal To Seasonal dataset (S2S) consists of global ensemble real-time forecasts and reforecasts from thirteen numerical weather prediction (NWP) and research centres. 
S2S project behind the dataset started in 2013 as a joint initiative of the World Weather Research Programme (WWRP) and the World Climate Research Programme (WCRP).
The goal of S2S project was to improve sub-seasonal forecast skill through combining multiple forecasting systems, enable multi-model evaluations and enhance knowledge sharing between operational centres.
Although S2S project ended at the end of 2023, data archiving continues and is currently undergoing another five-year phase (2024–2028).
There are two related datasets in ECDS:
- real-time forecasts (s2s-forecasts)
- reforecasts complementing the real-time data (s2s-reforecasts)
There are two types of the reforecasts - fixed and on-the-fly depending on the model and its current configuration.
The S2S reforecasts are covering varying periods since 1981. 
The typical forecast length is from 34 to 65 days (the same as in the real-time forecasts) with ensemble sizes varying from 4 to 33.
S2S variables are available on surface, soil, oceanic, potential temperature and selected pressure levels.
Please consult the Documentation section for details, including data sources, model configurations and limitations.
The data discovery and sample downloads can be done either via ECDS forms (under Download tab) or alternatively via dedicated MARS S2S catalogue (MARS stands for ECMWF's Meteorological Archival and Retrieval System).
(S2S picture used - courtesy of Mio Matsueda, S2S Museum)

ECMWF

S2S global sub-seasonal to seasonal ensemble reforecasts from multiple NWP and research centres since 2015

The International Grand Global Ensemble (TIGGE) dataset consists of global medium-range ensemble forecasts from thirteen numerical weather prediction (NWP) centres. 
The dataset has been available since October 2006. TIGGE was established as a key component of THORPEX: a World Weather Research Programme to accelerate the improvements in the accuracy of 1-day to 2 week high-impact weather forecasts (THORPEX stands for THe Observing system Research and Predictability EXperiment)
The typical forecast length is from 10 to 15 days with ensemble sizes varying from 12 to 51. Some centres also provide complementary high-resolution forecasts. TIGGE variables are available on surface, soil, potential temperature, potential vorticity and selected pressure levels.
Although the original ten-year THORPEX program ended at the end of 2014, data archiving continues and is currently undergoing another five-year phase (2024–2028).
Please consult the Documentation section for details, including data sources, model configurations and limitations.
The data discovery and sample downloads can be done either via ECDS forms (under Download tab) or alternatively via dedicated MARS TIGGE catalogue (MARS stands for ECMWF's Meteorological Archival and Retrieval System).
(TIGGE picture used - courtesy of Mio Matsueda, TIGGE Museum)

TIGGE global medium-range ensemble forecasts from multiple NWP centres since 2006

The Sub-seasonal To Seasonal dataset (S2S) consists of global ensemble real-time forecasts and reforecasts from thirteen numerical weather prediction (NWP) and research centres. 
S2S project behind the dataset started in 2013 as a joint initiative of the World Weather Research Programme (WWRP) and the World Climate Research Programme (WCRP).
The goal of S2S project was to improve sub-seasonal forecast skill through combining multiple forecasting systems, enable multi-model evaluations and enhance knowledge sharing between operational centres.
Although S2S project ended at the end of 2023, data archiving continues and is currently undergoing another five-year phase (2024–2028).
There are two related datasets in ECDS:
- real-time forecasts (s2s-forecasts)
- reforecasts complementing the real-time data (s2s-reforecasts)
The S2S real-time forecasts have been available since January 2015 (depending on the centre). 
The typical forecast length is from 34 to 65 days with ensemble sizes varying from 4 to 101.
S2S variables are available on surface, soil, oceanic, potential temperature and selected pressure levels.
The access to the S2S real-time data is allowed with a delay of 48 hours or 1 week depending on the centre (see details in S2S licence).
Please consult the Documentation section for details, including data sources, model configurations and limitations.
The data discovery and sample downloads can be done either via ECDS forms (under Download tab) or alternatively via dedicated MARS S2S catalogue (MARS stands for ECMWF's Meteorological Archival and Retrieval System).
(S2S picture used - WMO Lead Centre for Sub-seasonal Prediction Multi-Model Ensemble (example of Precipitation weekly mean anomalies))

Hours	Number of requests	Number of users	Downloaded data
Last 1H	1434	132	378 GB
Last 2H	2671	162	731 GB
Last 3H	4035	172	1115 GB
Last 6H	8722	207	1852 GB
Last 12H	16817	270	3430 GB
Last 24H	32335	334	6626 GB

	Catalogue entry	Number of users	Downloaded data
1	s2s-reforecasts	77	2974 GB
2	s2s-forecasts	134	2391 GB
3	tigge-forecasts	150	1768 GB

	Country	Number of requests	Number of users	Downloaded data
1	NO	60	1	124 GB
2	SE	19	2	95 GB
3	DE	315	8	75 GB
4	GB	2145	16	53 GB
5	AT	162	2	44 GB
6	IT	117	7	24 GB

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