Is there a way to guess if its going to rain based on pressure temperature humidity and cloud cover
If you live in a part of the world where the rainfall is dominated by frontal systems, and mainly by cold fronts, then there is a rough inverse correlation between pressure and rain. Otherwise, no. As Gerrit pointed out, rainfall is a whole lot more complicated than that. If you are looking for something to correlate with rain then I suggest you look into satellite-based cloud-top temperatures. The supercooled temperatures at the top of cumulus towers does correlate tolerably well with rainfall.