Redwing are very definitely bad weather visitors to Dorset. They come, usually with their cousins the fieldfare, every winter but the colder and more severe the weather 'up north' the larger the numbers we see here in the soft south. They are members of the thrush family who they nest in Scandinavia and far northern places and a trip to Dorset in winter is an escape from the tough winter conditions that set in up there in autumn and winter.
As the weekly chart shows clearly you can expect to start seeing redwing from week 40 (early October) until week 12 (end of March) the following spring. To see one outside this time frame is very unusual. There is no specific peak in reports caused through regular migration; peaks in redwing sightings usually coincide with bad weather.
You can encounter redwing almost anywhere in Dorset in winter. Most often they will be in hedgerows and in isolated trees near farmland. They are ground feeding birds in general but take to the trees and hedgerows for berries and also as an escape from disturbance or predators.
Telling you where and when you can reliably see redwing is impossible but as they are quite common in winter you should have no trouble in finding some somewhere in bad weather.