Be on the lookout for icicles in the coming days as we'll have almost ideal weather for them to form. You may have already seen some Tuesday afternoon with the return of sunshine. Sunny days, subfreezing temperatures and snow on the roof are pretty much all you need to get those beautiful, but yet dangerous, creations hanging from your porch or garage.
The sun, or some other heat source from the house (which could indicate a lack of insulation), melts the snow. But because the surrounding air is below freezing any melted snow will refreeze as it falls off the roof. The continuous melting and refreezing is what creates the very long icicles you sometimes see most often on the south facing side of a building. This is because of the location of the sun.
Icicles can be dangerous, though. And it's important to get rid of them safely, if you can, before they break off with milder weather.