The Met Office has issued a weather warning for the West Midlands - 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.
North Shropshire is set to be affected, as well as Cheshire 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."