Experts are warning that Storm Dennis will be a “step up” from the Storm Ciara which devastated the UK last week after a "perfect storm" of wet ground, snow and heavy rain.
The Environment Agency is urging people to sign up to its flood warnings service ahead of the arrival of the storm.
Director of Flood Prevention John Curtin said experts are still unsure exactly where the floods could hit but say that broadly Northern England, the Pennines, Wales, South West England remain at risk.
He said: "It's been a long winter already, many places are already saturated, we had a storm last weekend and that's why we're most concerned about this weekend coming."
Meanwhile Paul Davies, principal meteorologist at the Met Office, said much of the UK can expect between 20mm to 40mm of rain over the weekend, increasing to 50mm to 80mm in some areas.
Mr Davies said up to 140mm would not be "impossible" over the high ground of Wales and Scotland.
The "main areas of concern" on Saturday are north and south-west England, and Wales, followed by south east England on Sunday.
Storm Ciara, which hit the UK on Sunday, left 800 properties flooded in England alone, according to the EA.
Mr Curtin added: "The difference for us from a flooding point of view is now the ground is saturated from Storm Ciara last weekend and also especially in the North after Storm Ciara there was some snowfall in the Pennines and parts of Cumbria, and that snow will melt at the same time as the rain arriving and we'll get that double impact of melting snow and heavy rain."
He described it as a “perfect storm” with heavy rainfall falling on saturated ground at the same time that snow on higher ground is melting. The Met Office predicts most of the UK will see 20-40mm of rain with some seeing 50mm-80mm.
They warned that there could be potentially over 100mm while 120-140mm is not impossible.
Areas which have barely recovered from the onslaught of Storm Ciara are braced for further rain.
Last week devastated families near the river Calder were left fuming at the Tories’ failure to stop traumatic floods for the third time since 2012 after the river burst its back.
Homes and livelihoods were destroyed as the river swept through unfinished £33million flood defences. The EA highlighted flood prevention work they had already begun in Bradford on Avon, Billingdon, Ribchester, Frankwell, Shrewsbury, York and Ilkley.
Mr Curtin warned that this may just be the beginning for flooding this year.
He told journalists at a briefing on Friday: "In November I said I was concerned about this winter, I’m still concerned and it’s only February.”
He said: “We’re at some sort of ticking point", when it comes to protecting again flooding warning that it could not just be about building walls but about engaging with communities.
Members of the public are being encouraged to sign up to the flood warning system but Mr Curtin said it was important for those in areas liable to flood to also have a plan in place.
He cautioned: "If defences are overtopped the best thing people can do is move their own stuff.
"You can insure a fridge freezer or a car but move photographs, a kid’s drawing."
And advised them to think: "Where are my pills, where are my documents, what am I doing with my pets?'" as part of any plans.
