Special Report: COLA Forecast for Winter 1998 – North America
The Center for Ocean-Land-Atmosphere Studies, as part of its ongoing research into the predictability of seasonal to interannual climate variations, has prepared a forecast for the winter mean (January – March 1998 average conditions) based on information available as of 31 August 1997 (5-7 months lead forecast). While the forecast includes the entire globe, we provide a description for North America only. A more complete description of the forecast procedure and the models used is provided in an accompanying document .
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The forecast was prepared by first making a long lead forecast of the tropical Pacific sea surface temperature anomaly (SSTA) using an anomaly coupled model of the Earth’s climate. More information on the anomaly coupled model and the latest forecast of Pacific SSTA are available. The SSTA forecast of the anomaly coupled model is statistically projected to estimate a global SSTA (Figure 1) which is then applied as a lower boundary condition to the COLA global atmospheric general circulation model (AGCM). The COLA AGCM, which has been shown to exhibit skill in making seasonal climate forecasts for previous cases, is used to make the winter 1998 forecast.
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The forecast calls for generally warmer than normal conditions over most of North America (Figure 2). The bulk of the continental U.S. and Canada are predicted to experience warmer than normal seasonal average temperatures by at least 2° F. The largest departure from normal in the U.S. is in the northern plains where temperatures are forecast to be as much as 5-10° F above normal. Over the continent as a whole, the largest anomaly is forecast to occur in northern central Canada, where the temperature is predicted to exceed its normal value by as much as 15° F.
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The predicted precipitation (Figure 3) is generally above normal for the southern U.S. and Mexico and below normal for the northern U.S. and southern Canada. The extreme values for the seasonal average are forecast for northern California and central Mexico where over 10 inches more than the normal precipitation is predicted. The southwest U.S. and the states bordering the Gulf of Mexico are expected to receive over five inches more than normal precipitation for the season. Reductions in precipitation from the normal are forecast in the maritime provinces of Canada, the region near the Great Lakes, the high plains, and parts of the Canadian Rockies; however, these anomalies are modest in magnitude (about two inches below normal for the entire season).
To place this forecast in context, we have computed the
forecast skill for this model for the previous 16 winters
(JFM 1982 - JFM 1997). The anomaly correlation coefficient
is shown.
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In discussion of any climate forecasts produced by a numerical model, it must be stressed that there is a substantial element of uncertainty in any such product. For a discussion of that uncertainty, please refer to the full report.
The calculations required to produce this forecast were conducted as part of the Dynamical Seasonal Prediction project. Computing resources were provided at the Climate Simulation Laboratory of the National Center for Atmospheric Research Scientific Computing Division, and they are gratefully acknowledged.