We hereby inform you that the climatological base period applied to the APCC MME seasonal forecasts will be revised from 1991–2010 to 1993–2016.

• Effective Date: From the 2025 SONDJF forecast
• Purpose of Change: To reflect the most up-to-date hindcast data, considering the available hindcast years of participating models and the observed climatological based period(1991-2020).
• Details: This change applies only to the base period used for calculating forecast anomalies and climatological probability distributions. There will be no changes to forecasting methods, content structure, or data provision.

For further inquiries, please contact Ms. Yoorim Jung, Climate Prediction Department (yrjung@apcc21.org).