(In England) I never carry an umbrella, I just check the likely weather if I am going out (I use the forecast.io/ app on my iPhone now), and hope for the best. There is no particular time of day when rain is more or less likely in Britain, and BTW, the yearly rainfall in London in inches is about half that of a hot and humid town in the South of America. In London it may rain often but the rain is usually (not always but usually) extremely light compared to the torrential downpours you get in the States.
If it rains unexpectedly while I'm out I just shelter in a shop until it passes, or get a bus home instead of walking. I personally have no trouble knowing what to wear in England. It is in the hot and humid and torrential downpour parts of America where I have no clue what to wear. (Do you dress for the searing heat or the hot-bath rain??) In England, if it looks like rain when I am going to be out and about, I wear a light trench coat, an avant-garde hoodie, or simply long sleeves instead of no sleeves. (In the winter I am likely to be wearing something on the warm side anyway.) If I have to be out in more-USA-style (HEAVY) rain I might borrow a waterproof hooded rain jacket, but the fact that I do not myself own such a garment should tell you something about the rain here!
The rain here is indeed on the cold side, not warm (and if it rains a lot and you get soaked, you might feel cold), but it is not an extreme cold: England (esp the South, where I live) is very mild and temperate. Dressing is much easier in Britain than in some parts of USA. You don't have to keep adding and removing layers etc. Compared to America, it never gets that hot or that cold, and nor does it feel humid, regular sprinkles of rain notwithstanding. I had never experienced that walking-in-a-warm-bath humidity until I went to America, and nor had I ever experienced hot rain until I went there.
