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GFDL’s New Modeling System for Seasonal Predictions

GFDL’s newly developed SPEAR modeling system will be used to produce real-time experimental seasonal predictions each month. These are used by NOAA’s National Weather Service (NWS) in support of operational forecasts, seasonal outlooks, and scientific research. Predictions made with SPEAR have improved skill for many aspects of the Earth’s climate system, including the El Niño-Southern Oscillation (ENSO), precipitation and temperature over North America, and Arctic sea ice.

As of February 6, 2021, SPEAR becomes part of the North American Multi-Model Ensemble (NMME), an effort led by NWS’s Climate Prediction Center to combine multiple global systems to generate seasonal predictions and support operational seasonal outlooks (temperature, precipitation, Atlantic hurricane outlook, winter outlook, etc.). At the beginning of each month, GFDL scientists gather observations from around the world to be used as starting points for the SPEAR system, to make climate predictions for the following 12 months. A total of 30 ensemble members will be provided for probabilistic prediction purposes. These computer-based predictions are conducted on NOAA’s state of the art GAEA supercomputer located in Oak Ridge, TN. This SPEAR seasonal prediction data can be accessed from the NMME website.

In addition to real-time experimental predictions, the new SPEAR system will be used as the foundation for ongoing research toward improving climate predictions and projections on timescales from one season to multiple decades ahead, with a focus on climate extremes. These extremes include hurricanes, drought, heat waves, atmospheric rivers, and hydrologic extremes. The SPEAR system also is used to make decadal climate predictions that are transmitted to the UK Meteorological Office as part of a World Meteorological Organization international collaborative activity.

The new SPEAR system shares many components with the latest GFDL climate model CM4 and utilizes the most recently developed initialization system. The relatively high global atmospheric/land resolution (50 km) of SPEAR provides information on climate extremes, and at regional scales. The SPEAR system also produces estimates of the current state of the ocean that will be provided to NWS’s National Center for Environmental Prediction, as well as the Australian Bureau of Meteorology, as part of an international scientific comparison.

The newly developed SPEAR model replaces GFDL’s older prediction system in use since 2015 that used the CM2.1 and FLOR models.

FIGURE: SPEAR-based predictions of eastern tropical Pacific (Niño 3.4 region) sea surface temperature anomalies (relative to long-term monthly climatology). Negative values indicate colder than normal conditions (La Niña-like). The forecasts were started based on observed conditions on January 1, 2021. The dark solid line is the 30-member ensemble mean, and the dashed lines represent the various ensemble members. The model predicts a transition from current La Niña conditions to more neutral conditions in summer, 2021, and then a possible return to La Niña conditions in Fall, 2021. Uncertainty in the prediction is indicated by the scatter of the various ensemble members around the ensemble mean.