December 2025 Climate Forecast Discussion
December 2025 Climate Forecast Discussion for the period Jan-Mar through Apr-Jun 2026
**Note: ** The CCSR/IRI seasonal forecasts of precipitation and temperature issued this month are based on an objective calibration procedure that combines four models NCEP-CFSv2, CanSIPS-IC4, COLA-RSMAS-CESM1, and NASA-GEOSS2S models. The climatological base period for normal is 1991-2020. The SST anomalies cited below refer to the OISST.v2.1 SST data set. Starting from June 2024, the observed climatology used to compute the dry mask was updated to 1991-2020, and the criterion modified to mask points where 10% of the training sample (i.e. 3 or more years) received less than or equal to 1 mm over a 3-month season.
In November 2025, sea surface temperature (SST) anomalies crossed the La Niña threshold in the central-eastern equatorial Pacific Ocean, with the monthly Niño 3.4 anomaly index at -0.68 °C. Weekly averaged SST anomalies in the Niño 3.4 region reached -0.7 °C for the week centered on November 10, 2025, indicating persistent cooler sea surface temperatures. The early December CPC Forecast maintained a “La Nina Advisory”. According to the statement, La Niña is favored to continue for the next month or two, with a transition to ENSO-neutral most likely in January–March 2026 (68% chance). The Indian Ocean Dipole (IOD) index was negative in November 2025 but transitioned to a neutral state in December 2025. Meanwhile, the North Atlantic Ocean continued to exhibit slightly warm SST anomalies, although they decreased substantially. Additionally, the Pacific Decadal Oscillation (PDO) index recorded a value of -1.67 for November 2025.
The CCSR/IRI Multi‑Model Probability Precipitation Forecast for January–March (JFM) 2026 shows a high likelihood of above‑normal precipitation (green shading) across Central America, northern South America, equatorial Africa, and the Maritime Continent, and below‑normal precipitation (yellow to brown shading) over Mexico, the western and southern United States, around Uruguay, and northeastern China. As the forecast progresses into February–March and the subsequent March–May and April–June seasons, these wet and dry signals weaken considerably, with probabilities for both above‑ and below‑normal precipitation becoming muted and most regions reverting to near‑climatological odds. The muted signals beyond boreal winter are consistent with a weaker ENSO influence, as La Niña conditions are expected to decay to ENSO‑neutral around the start of 2026 and remain neutral through the forecast period.
The temperature forecasts show a strong tilt toward above‑normal temperatures (red shading) in nearly all seasons across much of North America, northern and central Eurasia, the Middle East, and large parts of Africa and South America. Below‑normal temperatures (blue shading) are confined mainly to the western half of Canada during JFM 2026. Near‑normal conditions (gray shading) during JFM and FMA, especially over portions of South America, Africa, and Australia, mark regions where the normal‑temperature category is most likely, indicating outcomes close to the climatological median.