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Guessing Mother Nature's Next Move

What can be done to improve weather prediction and load forecasts?

Fortnightly Magazine - August 2005

Therefore, the Cal-ISO built a "temperature spike predictor," which compensated for this deficiency. Used for the summer of 2004, this temperature forecast, combined with the forecast from our commercial forecaster, resulted in a significant improvement. The Cal-ISO published day-ahead load forecast accuracy (in terms of mean absolute percent error) dropped from 1.91 for 2003 to 1.66 for 2004, and large errors dropped another 19 percent. These overall accuracy figures include model error, weather error, and pumping error.

In conclusion, weather forecast error is significant and has costs to suppliers, transporters, and consumers. While practitioners take solace that their forecasts errors average in the range of 1 to 2 percent per year, these errors do add up to significant costs over a year. In addition, extreme weather events can occur, as they do in most regions of the United States, and this often occurs during very high cost periods. Managing weather and load forecast error both of a small nature and for those larger events is very cost-effective. How cost-effective depends on the individual power system, weather phenomena, the load, and modeling tools used.

Given that load imbalances and congestion accumulate significant costs in competitive power markets, more and more attention will be devoted to benchmarking the errors and finding more advanced solutions to reduce their magnitude. Clearly, more accurate weather forecasting can make a significant improvement in load forecasting, as well as reduction of costs.



  1. NOAA, The Northeast Energy Network Performance Analysis Report: Final Report (August 2003); NOAA, The Use of 30 Year Climate Forecasts To Improve Regional Long-Range Energy Infrastructure Planning for San Diego County); NOAA, The Economic Benefits of Incorporating Weather and Climate Forecasts into Western Energy Production Management.

* The work by Dennis Gaushell ( was performed for the California ISO. The authors acknowledge the contribution of L. Heitkemper of EarthSat, Jan Dutton of AWS, and Alexander Gershanov of the Scripps Institution of Oceonography.