Motorists in Cheshire and the Wirral are being advised to plan extra time into their journeys as thick fog is forecast across the region.
The Met Office has issued a yellow weather warning for the North West of England - saying fog will become "increasingly widespread".
The yellow warning is in place from 7pm on Wednesday night and is due to cease at 11am on Thursday morning.
Cheshire and the Wirral are set to be affected, as well as Merseyside, Shropshire and vast areas of Wales.
A Met Office spokesman said: "Slower journey times are possible and there is a chance of delays to flights."
They added: "Fog patches are likely to form during the early part of Wednesday evening, becoming more widespread overnight with the visibility falling below 100m in places."
"Fog will thin slowly later on Thursday morning, although some patches may persist into the afternoon in the west of the warning area."