North American Ensemble Forecast System (NAEFS)

The North American Ensemble Forecast System (NAEFS) is a joint project involving the Meteorological Service of Canada (MSC), the United States National Weather Service (NWS) and the National Meteorological Service of Mexico (NMSM). NAEFS was officially launched in November 2004 in presence of representatives of the three countries.

NAEFS combines the state-of-the-art ensemble forecasts run by the MSC's Global Environmental Multiscale Model and the NCEP Global Spectral Model. When combined, the grand ensemble provides weather forecast guidance for the 0-384 hours that is of higher quality than the currently available operational guidance based on either set of ensembles alone. It allows the generation of a set of forecast products that are seamless across the national boundaries between Canada, the United States and Mexico. The research/development and operational costs of the NAEFS system are shared by the three organizations (MSC, NWS, and NMSM), which make it more cost effective and result in higher quality and more extensive weather forecast products.

NAEFS forecast graphics and information can be found at:

- Official NAEFS graphics at the NCEP Model Analysis and Guidance Page

- NAEFS Verification

- NCEP Climate Prediction Center NAEFS 8-14 day outlooks

- NCEP Climate Prediction Center NAEFS 6-10 day precipitation forecast

- List of NAEFS Products produced by NCEP

- Meteorological Service of Canada (MSC) NAEFS web site


NAEFS configuration as of April 2016

Models NWS Global Forecasting System (GFS) and

MSC Global Environmental Multiscale Model (GEM)

Daily Frequency 0000 UTC and 1200 UTC
Forecast Length 16 days
Initial Condition Uncertainty Ensemble Kalman Filter (EnKF)
Control 1 NWS + 1 MSC
Ensemble Members 40 (20 NWS + 20 MSC) for each cycle
Post-Processed Probabilistic


mean, mode, standard deviation,

and probabilities (10%, 50%, 90%)

Post-Processed Probabilistic

Product Resolution

NWS/MSC: 1 deg x 1 deg global products

NWS: downscaled CONUS 2.5 km, Alaska 3 km


References for GEFS, NAEFS and post processing:

Cui, B., Z. Toth, Y. Zhu and D. Hou, 2012: Bias Correction For Global Ensemble Forecast, Weather and Forecasting, 27, 396-410

Cui, B., Y. Zhu, Z. Toth and D. Hou, 2018: Development of Statistical Post-processor for NAEFS. To be submitted to Weather and Forecasting

Guan, H., B. Cui, Y. Zhu, 2015: Improvement of Statistical Postprocessing Using GEFS Reforecast Information, Weather and Forecasting, Vol. 30, 841-854

Hou, D., Z. Toth, Y. Zhu, W. Yang and R. Wobus, 2012: "A Stochastic Total Tendency Perturbation Scheme Representing Model- Related Uncertainties in the NCEP Global Ensemble Forecast System" Submitted to Tellus-A)

Hou, D., M. Charles, Y. Luo, Z. Toth, Y. Zhu, R. Krzysztofowicz, Y. Lin, P. Xie, D-J. Seo, M. Pena and B. Cui, 2012: Climatology-Calibrated Precipitation Analysis at Fine Scales: Statistical Adjustment of STAGE IV towards CPC Gauge-Based Analysis, Jaurnal of Hydrometeorology Vol. 15 2542-2557

Liu, Q., S. J. Lord, N. Surgi, Y. Zhu, R. Wobus, Z. Toth and T. Marchok, 2006: Hurricane Relocation in Global Ensemble Forecast System, Preprints, 27th Conf. on Hurricanes and Tropical Meteorology, Monterey, CA, Amer. Meteor. Soc., P5.13.

Ma, J., Y. Zhu, D. Wobus and P. Wang, 2012: An Effective Configuration of Ensemble Size and Horizontal Resolution for the NCEP GEFS, Advance in Atmospheric Sciences, Vol. 29, No. 4, 782-794

Ma, J., Y. Zhu, D. Hou, X. Zhou and M. Pena, 2014: Ensemble Transform with 3D Rescaling Initialization Method, Monthly Weather Review, Vol. 142, 4053-4073

Palmer, T. N., R. Buizza, F. Doblas-Reyes, T. Jung, M. Leutbecher, G. Shutts, M. Steinheimer, and A. Weisheimer, 2009: Stochastic Parametrization and Model Uncertainty. ECMWF Tech. Memo. 598, 44.

Shutts, G., 2005: A kinetic energy backscatter algorithm for use in ensemble prediction systems. Quart. J. Roy. Meteor. Soc., 131, 3079-3102.

Toth, Z., and E. Kalnay, 1997: Ensemble forecasting at NCEP and the breeding method. Mon. Wea. Rev., 125, 3297-3319.

Wei, M., Z. Toth, R. Wobus, and Y. Zhu, 2008: Initial Perturbations Based on the Ensemble Transform (ET) Technique in the NCEP Global Operational Forecast System, Tellus 59A, 62-79

Whitaker, Jeffrey S., Thomas M. Hamill, Xue Wei, Yucheng Song, Zoltan Toth, 2008: Ensemble Data Assimilation with the NCEP Global Forecast System. Mon. Wea. Rev., 136, 463-482.

Zhou, X., Y. Zhu, D. Hou, Y. Luo, J. Peng and R. Wobus, 2017: The NCEP Global Ensemble Forecast System with the EnKF Initialization. Wea. Forecasting, 32, 1989-2004. 

Zhu Y., and Y. Luo, 2014: Precipitation Calibration Based on Frequency Matching Method (FMM), Weather and Forecasting, Vol. 30, 1109-1124