We present a prediction scheme for specifying the duration and maximum strength of the southward IMF within a magnetic cloud from observations of the disappearing filament associated with the coronal mass ejection and the photospheric magnetic field made near the filament disappearing. Using this scheme we were able to predict that the Earth directed 6 January 1997 coronal mass ejection would be geoeffective. We expected that the southward IMF interval would have a maximum strength of -13¿5 nT and a duration of 14¿5 hours. This compares favorably with the WIND observations of -15 nT and 13 hours. ¿ 1997 American Geophysical Union