The Met Office has issued an amber warning for rain between 3pm on Saturday, February 15 and 3pm on Sunday February 16.
Storm Dennis is likely to bring very heavy rain, flooding and disruption to travel over the weekend.
The Environment Agency has issued a "medium" flood risk level for the Lancaster district, meaning flooding is expected and people should be prepared.
It advises people to check the latest flood warning information, be alert and monitor local weather conditions, consider postponing any travel plans and avoid driving or walking through flood water.
The Environment Agency says that river and surface water flooding is possible widely across the north of England from later on Saturday through Sunday and is probable for parts of the Pennines and upland areas of south Wales.
Mores strong winds are forecast from 1pm on Saturday February 15, throughout Sunday and into Monday.
The forecast for the weekend follows similar conditions to last weekend, February 9, when Storm Ciara caused the River Lune to burst its banks and resulted in flooding of properties and businesses.