Train passengers in Todmorden, Hebden Bridge, Halifax, Sowerby Bridge and Mytholmroyd face disruption due to hot weather
People in Calderdale should expect disruption to train journeys this week, Northern has warned.
The train operator said services between Manchester Victoria and Leeds via Bradford Interchange may be cancelled, delayed or reduced, with disruption expected until the end of the day on Thursday.
High temperatures have been forecast across the UK this week, with the Met Office issuing amber heat alerts for Manchester and Leeds which will come into force on Wednesday and Thursday.
Northern said the forecasted severe weather means that fewer trains are able to run on all lines.
Affected stations in Calderdale include Todmorden, Hebden Bridge, Halifax, Sowerby Bridge and Mytholmroyd.
Customers can expect fewer trains on some lines, some timetabled services not to run, and for services that do run to be busier than usual.
The operator said it will introduce a reduced timetable from Tuesday (today) to Thursday, and that temporary speed restrictions are in place on some routes.
It said extreme heat can affect train performance and reliability.
It advised customers to check before they travel, and that it will continue to monitor conditions closely and may make further changes.
Northern advised customers to allow extra time for their journey, to travel earlier if possible to avoid the busiest services, to bring water to stay hydrated, and, if they feel unwell, to not board the train and to speak to a member of staff for help.
A national ticket easement policy is in place, which customers can find out more about on the Northern website.