Typically to get a transition zone that mixes with overrunning events. Basically the cold front stalls over our region and warm moist air to the south is what is both providing the moisture as well as warming the mid levels, while cold air reinforces itself from the cold/dry air to the north. An overrunning event can produce heavy wintry precip without a strong low pressure system developing along the boundary at all, although this does tend to happen eventually as the push of warm air occludes with the cold front once it rounds the corner of the trough.
https://www.saltwire.com/atlantic-canada/behind-the-weather-the-science-behind-overrunning-100931920