Questions about geese migration

I live in Fife, so all month I've been seeing geese flying back and forth in their classic V formation. Today, however, has been a particularly busy day in the skies. I've been way above average numbers of geese flying over. 

So I have two questions. Firstly, are these geese that are just arriving, or are they coming either to or from their roost to feed in the fields nearby? I remember reading that large quantities of geese roost in Montrose basin which is just up the coast. Are the birds I'm seeing likely to be birds that are coming from there to feed, or are these birds that are just arriving?

Secondly, what is it about today that's caused the massive increase in the number of birds? I'm sure there are a few factors, but is is to do with the weather, or time of year, or something else?

Thanks in advance for any answers!