I certainly agree with you regarding the weather turning for the worst at weekends Paul.
I'm lucky to be able to pick and choose my visits to the bank nowadays after decades of weekend only trips regardless of conditions. Like many keen anglers who have a go when all their instincts are telling them to have another couple of hours in bed I've spent many hours sitting out in freezing floods.
As always much depends on which way the temperature is going and locating the fish.
A warm outfall is often a holding spot in freezing flood if you can put up with the extra amounts of sewerage that often gets pumped out during these conditions!
As mentioned, a lobworm fished in a slack or flooded side stream may produce a bonus fish.
I would put barbel and chub towards the bottom of the target list and rove the bank for pike. If you happen to know where one or two of the big old girls lay up in cold coloured flood a good fish can almost be a forgone conclusion.
It's often easy to see that pike don't move about much in prolonged flood by the large amount of leeches and lice that have attached themselves to a captured fish through inactivity.
I prefer cold clear rivers for piking and chub, and for some reason have often done well when it's snowing,.. perhaps it's because during a freeze up the temperature can rise slightly when it snows?
Again, as mentioned, an unfrozen stillwater can be very handy when the going gets tough on the rivers or a decent boozer of course!