Opinion polls published in the media are very often misinterpreted leading to claims of polling errors or bias. When most polls indicated a very narrow victory for one side and the election then turns out a very narrow victory to the other side that does not mean there was any error in the polls, but frequently stems from people only reading the topline results and taking them as a deterministic prediction. To overcome this, some models have been developed, mainly in the United States, that use poll data to assign specific probabilities to each possible outcome. In addition to providing a more honest way of presenting prediction based on opinion polls, these models use a systematic processing of polling data and past election results, in addition to other data sources, that provides insight into the main factors driving shifting voting patterns. Since there are very few studies of this kind done for european countries, we aim to develop an electoral model for the portuguese parliamentary elections that can, along the way, maybe reveal some interesting national and regional voting patterns in the country along the last few decades.