# C3S seasonal models anomaly **URL:** \ **Category:** C3S - Datasets and Usage\ **Tags:** seasonal\_forecast, c3s\ **Created:** [21 September 2022 12:38 UTC](https://forum.ecmwf.int/t/c3s-seasonal-models-anomaly/1149 "2022-09-21T12:38:47Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![gabrielcassol](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/g/9f8e36/32.png) [@gabrielcassol](https://forum.ecmwf.int/u/gabrielcassol)\ **Post date:** [21 September 2022 12:38 UTC](https://forum.ecmwf.int/t/c3s-seasonal-models-anomaly/1149/1 "2022-09-21T12:38:47Z")
I would like to know what is the period of climatology used in these products to calculate the anomalies? I couldn't find this information anywhere in the product description. "Seasonal forecast anomalies on **single** levels": [https://cds.climate.copernicus.eu/cdsapp#!/dataset/seasonal-postprocessed-single-levels?tab=overview](https://cds.climate.copernicus.eu/cdsapp#!/dataset/seasonal-postprocessed-single-levels?tab=overview) "Seasonal forecast anomalies on **pressure** levels": [https://cds.climate.copernicus.eu/cdsapp#!/dataset/seasonal-postprocessed-pressure-levels?tab=overview](https://cds.climate.copernicus.eu/cdsapp#!/dataset/seasonal-postprocessed-pressure-levels?tab=overview) ---
**Author:** ![Yassmin\_Hesham\_Hanfi](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/y/90db22/32.png) [@Yassmin\_Hesham\_Hanfi](https://forum.ecmwf.int/u/Yassmin_Hesham_Hanfi)\ **Post date:** [23 September 2022 07:20 UTC](https://forum.ecmwf.int/t/c3s-seasonal-models-anomaly/1149/2 "2022-09-23T07:20:18Z")
As I understood,  it has been done based on the hihndcast period available on CDS (1993-2016) ---
**Author:** ![Eduardo\_Penabad](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/e/6a8cbe/32.png) [@Eduardo\_Penabad](https://forum.ecmwf.int/u/Eduardo_Penabad)\ **Post date:** [26 September 2022 09:04 UTC](https://forum.ecmwf.int/t/c3s-seasonal-models-anomaly/1149/3 "2022-09-26T09:04:18Z")
Dear Luiz Gabriel, as you have pointed out this is something that probably should be better documented in the CDS. In any case, I can confirm you the anomalies provided in the two datasets you mentioned are calculated using **the common reference period used for seasonal forecast products on the C3S, and that is from 1993 to 2016**. Apologies for the suboptimal level of information you've found, we'll try to improve that in future iterations of our documentation. Regards, Eduardo Penabad C3S Climate Predictions and Projections Team ---
**Author:** ![Juan\_Camilo\_Giraldo](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/j/ecb155/32.png) [@Juan\_Camilo\_Giraldo](https://forum.ecmwf.int/u/Juan_Camilo_Giraldo)\ **Post date:** [3 June 2025 10:28 UTC](https://forum.ecmwf.int/t/c3s-seasonal-models-anomaly/1149/4 "2025-06-03T10:28:34Z")
Hello. I was trying to access this dataset throught the API but its not found within the available datasets: 404 Client Error: Not Found for url: [https://ads.atmosphere.copernicus.eu/api/retrieve/v1/processes/seasonal-postprocessed-pressure-levels](https://ads.atmosphere.copernicus.eu/api/retrieve/v1/processes/seasonal-postprocessed-pressure-levels) Do you know if there a solution to this? Thank you ---
**Author:** ![Michela](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/m/898d66/32.png) [@Michela](https://forum.ecmwf.int/u/Michela)\ **Post date:** [3 June 2025 11:06 UTC](https://forum.ecmwf.int/t/c3s-seasonal-models-anomaly/1149/5 "2025-06-03T11:06:56Z")
Hi, please check the you have the right URL. You can copy that from here (please log in first): [CDSAPI setup - Climate Data Store](https://cds.climate.copernicus.eu/how-to-api) Thanks