The major goal of this manuscript is the improvement of a methodology to predict rainfall as a function of time; how far the solar activities and other components of the climate system are alternatives. For this purpose one makes use of computer simulation environment with neural network and stochastic analyses. The possible statistically significant correlation between sunspot numbers and regional precipitation was investigated, considering thirteen (13) meteorological stations over Portugal mainland in the period of 1951–2004. The data analysis shows signs that the relationship between the solar activity and the climate of Portugal is in any way exceptional. Possibly, the Portuguese climate system (primarily considering rainfall) is more sensitive to sensible variations in solar activity than generally believed! The conclusion highlight the use of solar activity response as potential climate or rainfall predictor, even though the relative importance of sunspot numbers compared to established meteorological factors responsible for rainfall is probably hard to quantify.