Urgent weather warnings have been issued for rain across the country.
The Met Office says flooding and disruption could be the result of heavy rainfall from today - and extend into tomorrow.
Saturday's warning covers the whole of the north and the south west and is in place between lunchtime and midnight on Saturday. Thunderstorms are also expected. Areas the warning covers are Yorkshire and the Humber, south west England, the West Midlands, the East Midlands, London and south east England, the east of England and Wales.
Sunday's warning is in place from midnight on Saturday to 6am the following morning. It covers the whole of the north and the south east. Areas the warning covers are the East Midlands, Yorkshire and the Humber, the east of England and London and south east England.
Forecasters at the Met Office says people should expect flooding of homes and businesses and transport to be affected.
There is also a good chance power could be affected and damage could ensue due to lightning strikes, the Met Office says.
A spokesman said on Saturday it is likely that there will be "outbreaks of rain, heavy at times, moving north and east across many areas, then turning bright across southern, western and later some central parts, but with showers, heavy and thundery in places.
"On Saturday night, heavy rain or showers could become restricted to parts of northern and eastern England whilst dying out elsewhere. Mist and low cloud in the north and east.
"On Sunday, rain in the east is expected to clear, with cloud breaking to allow sunny intervals for most areas. Some showers may develop but many southwestern areas may remain dry."
The Met Office says a yellow weather warning is issued when it is likely the weather will cause some low level impacts, including some disruption to travel in a few places.
It says: "Many people may be able to continue with their daily routine, but there will be some that will be directly impacted and so it is important to assess if you could be affected. Other yellow weather warnings are issued when the weather could bring much more severe impacts to the majority of people but the certainty of those impacts occurring is much lower."
