A yellow weather warning for torrential rain, hail and thunderstorms has been issued for the north west, say the Met Office.
Forecasters warn that the stormy weather could see some areas affected by localised flooding with a possible disruption to power supplies.
The extensive thunderstorms are expected to break out later on this afternoon leading to torrential downpours, lightning and a chance of hail, they added.
A spokesman for the Met Office said: "Bouts of rain, heavy and thundery at times, will move in from the west to affect parts of southern Scotland and northern England from the early hours of Wednesday.
"More extensive thunderstorms may then break out over a larger part of England and Wales from late Wednesday afternoon onwards into Wednesday night, leading to torrential downpours, frequent lightning and a chance of hail.
"This could result in some disruption, more likely from late Wednesday afternoon, which may include sudden localised flooding of transport routes, homes and businesses.
"Frequent lightning in association with the heaviest rain may also temporarily disrupt power supplies.
"However, many places will likely see little or no impacts. Indeed many parts of the warning area will see dry and sunny weather through much of the daytime on Wednesday."
The warning is in place from 3am on Wednesday June 21 until 6am on Thursday June 22.