There are delays of up to one hour between London Paddington and Cardiff Central, and between London Paddington and Bristol Temple Meads due to flooding between Swindon and Bristol Parkway.
Services are running to Bristol and South Wales but delays and cancellations are expected throughout the day.
Icy by night, chilly by day - brace yourself for a cold week ahead.
High pressure keeps the weather chilly by day, icy by night, with an increasing risk of freezing fog.
High pressure this weeks means mainly cold bright days and icy cold nights.