  We employ remote observations of coronal mass ejections (CMEs) and the
associated solar flares to forecast the CME-related Forbush decreases, i.e.,
short-term depressions in the galactic cosmic-ray flux. The relationship
between the Forbush effect at the Earth and remote observations of CMEs and
associated solar flares is studied via a statistical analysis. Relationships
between Forbush decrease magnitude and several CME/flare parameters was found,
namely the initial CME speed, apparent width, source position, associated
solar-flare class and the effect of successive-CME occurrence. Based on the
statistical analysis, remote solar observations are employed for a
Forbush-decrease forecast. For that purpose, an empirical probabilistic model
is constructed that uses selected remote solar observations of CME and
associated solar flare as an input, and gives expected Forbush-decrease
magnitude range as an output. The forecast method is evaluated using several
verification measures, indicating that as the forecast tends to be more
specific it is less reliable, which is its main drawback. However, the
advantages of the method are that it provides early prediction, and that the
input is not necessarily spacecraft-dependent.
