Climate Impacts Group home page Land Surface Hydrology Research Group home page National Oceanic and Atmospheric Administration GEWEX Americas Prediction Project

One year lead-time experimental streamflow forecasts for the Columbia River at The Dalles

Past Forecast Performance

What is the Performance Record of the ENSO Forecasts since 1998?

This figure from the data archives of the IRI shows the time history of the NINO3.4 time series (sea surface temperature anomalies in degrees C). The retrospective definition of ENSO state that we use for forecasting is based on 0.5 standard deviations from the long-term mean (+/- 0.47 degrees C) of the NINO3.4 index averaged from December to February (PDO ENSO Tables). We have been interpreting ENSO forecasts delivered in about the first week of June since 1997.

ENSO forecasts for water year 1998, 1999, 2000, 2002, and 2003 (warm, cool, cool, neutral, warm respectively) made in June proved accurate. The ENSO forecast for 2001 predicted the highest likelihood of ENSO neutral conditions in June, but during the winter the sea surface temperatures exceeded the threshold for the cool ENSO category, so our interpretation of the ENSO forecast in June was in error. The streamflow forecast for 2001 would have been even more in error if we had had a correct forecast of cool ENSO, so the incorrect ENSO forecast was not the predominant source of forecast error in 2001 as it turned out.

For water year 2004, the ENSO forecast available in June 2003 for the winter 2003-2004 proved to be incorrect. By October 1, however, an updated forecast of ENSO neutral conditions was released. This forecast proved to be accurate.

How did we do in 2003 and 2004?

The long-range streamflow forecast in for water year 2003 was very skillful, with the observations very closely matching the ensemble mean. In the 2004 water year, the observed streamflow (through August 2004) was near the bottom of the forecast ensemble. These conditions may be partly explained by the wide spread drought occuring over much of West, the cause of which is only partly understood.

For more details, see Forecast Archive.

August 25, 2005