Because the CCA (Barnston 1994) and OCN (Huang et al. 1995) methods are now being used for the official operational long-lead seasonal forecasts issued by the Climate Prediction Center of NCEP, they are not presented in detail in this Experimental Bulletin. However, a brief summary of these forecasts, as well as that of the NCEP coupled model using forecast SSTs (Ji et al. 1994), are provided for Jan-Feb-Mar 1998. For more information about the official NCEP forecasts, the following U.S. Regional Climate Center (RCC) Offices may be contacted:
Northeastern RCC 607-255-5950
Southeastern RCC 803-737-0800
Southern RCC 504-388-5021
Midwest RCC 217-244-8226
High Plains RCC 402-472-8294
Western RCC 702-677-3106
The forecasts themselves are contained in the Climate Outlook,
available on Internet with address: http://nic.fb4.noaa.gov. That same
address can also be used to access the web site for this Bulletin, as follows:
http://nic.fb4.noaa.gov; then click on "predictions", then click on "experimental
long-lead".
U.S. Surface Climate Forecasts for Jan-Feb-Mar '98Temperature: CCA predicts warmth in the far west, north central states and Great Lakes area, New England, and the inner Aleutians and Alaska panhandle; cold in much of the Southeast and northern Hawaiian islands. OCN predicts warmth across the East and the West (especially the Southwest). The NCEP coupled model using forecast SST predicts warm across the northern U.S., cold in southern Texas and most of New Mexico.
Precipitation: CCA predicts dry northern Plains, Great Lakes, Ohio Valley and all of Hawaii except the Big Island; wet extreme south such as Florida, southern Texas and Arizona, and parts of Alaska. OCN forecasts dry in Ohio Valley, wet in portions of the South. The NCEP coupled model using forecast SST predicts wet in the southeastern, southwestern and far western U.S., dry in Ohio/Tennessee Valleys.
Note: The above forecast descriptions include only regions whose estimated cross-validated correlation skill exceeds 0.3. Highest local skills are usually in the neighborhood of 0.6, but this varies with season, lead time and forecast tool.
ENSO-Related SST
CCA (Barnston and Ropelewski 1992, Smith et al. 1995) predicts warming of the SST in Niño 3.4 (120-170oW, 5 oN-5 oS) to "high-neutral" by this spring, strengthening into moderate warm episode conditions (with low confidence) by fall and continuing through winter 1997-98. Specifically, CCA forecasts the following standardized anomalies and cross-validated correlation skills:
| Forecast | Skill | |
| Oct-Nov-Dec 1997 | 2.71 | 0.91 |
| Jan-Feb-Mar 1998 | 2.77 | 0.86 |
| Apr-May-Jun 1998 | 1.89 | 0.65 |
| Jul-Aug-Sep 1998 | 0.36 | 0.30 |
| Oct-Nov-Dec 1998 | -0.18 | 0.22 |
The forecast for Oct-Nov-Dec 1997 is a skill-weighted average of CCA and simple persistence of the anomaly observed in Jun-Jul-Aug, because persistence and CCA skills are similar for that forecast. Longer lead forecasts reflect only CCA. The global field of SST anomaly for Sep 7-13 1997 (Fig. 1) shows that the SST along the eastern and central equatorial Pacific is far above normal. Observations as anomalously positive such as these at this time of year nearly guarantee El Niño conditions for the remainder of 1997 and winter 1997-98.
Barnston, A.G., 1994: Linear statistical short-term climate predictive skill in the Northern Hemisphere. J. Climate, 5, 1514-1564.
Barnston, A.G. and C.F. Ropelewski, 1992: Prediction of ENSO episodes using canonical correlation analysis. J. Climate, 7, 1316-1345.
Huang, J., H.M. van den Dool and A.G. Barnston, 1996: Long-lead seasonal temperature prediction using optimal climate normals. J. Climate, 9, 809-817.
Ji, M., A. Kumar and A. Leetmaa, 1994b: An experimental coupled forecast system at the National Meteorological Center: Some early results. Tellus, 46A, 398-418.
Reynolds, R.W. and T.M. Smith, 1994: Improved global sea surface temperature analysis using optimum interpolation. J. Climate, 7, 929-948.
Smith, T.M., A.G. Barnston, M. Ji and M. Chelliah, 1995: The impact of Pacific Ocean subsur-face data on operational prediction of tropical Pacific SST at the NCEP. Wea. Forecasting, 10, 708-714.
Fig. 1. NCEP optimum interpolation (OI; Reynolds
and Smith 1994) global SST anomaly field for the week of September 7-13,
1997.
