I don't think weather radar is much use for forecasting more than the next few hours.
Sat24 has a good moving photo which will show you radar images for the last 2 hours, which you can use to get an idea of the immediate trends, and spot any potential approaching clouds (or gaps in the clouds, if it's already raining).
I use Weather Online for most of my forecasting. If you look at their Expert Charts section (
here's one for the rain in Spain 
) you can find forecasts for up to 384 hours (about 2 weeks) ahead - though I wouldn't pay too much attention to the forecast at that range.
As others have said, 7-day forecasts are not terribly reliable. One trick to gauge the accuracy is to watch how the forecast for the day(s) in question changes over several days. If the forecast remains reasonably consistent, it means that the computer model used to create the prediction is fairly confident. If the forecast is inconsistent, it means that the model is undecided about what's brewing and the forecast is less reliable.
You can use the Weather Online site to look at how consistent the forecast has been. In weather-geek speak, a "model run" is a forecast at a certain time (they run a computer program based on the software model, and the forecast is based on the output of the model run.)
On the WO site you can actually change the base model run to see how consistent the forecast has been. They publish an updated forecast every 6 hours, but they display historical forecasts as well. In fact, by selecting Base=all you can easily view the forecast history. For example,
here's the forecast history for Tuesday 23rd, most recent forecasts at the top. Pretty much all the model runs since last Friday have predicted light rain over NW Spain, so the model seems fairly confident about it, and I would therefore count on it.
Of course, in mountainous regions there are all sorts of other factors like microclimates, whether you are on the windward or leeward side of the hills (usually more rain upwind of hills) etc, hence forecasts are likely to be of general use only ("I might head North up to the coast" vs "I might head South" vs "I might stay in and keep dry").