Consistent terrain to run on can limit your ability to run fast during the winter months. If snow and ice are a regular occurrence in your hometown it can be tough to run fast while staying safe. Including even small amounts of faster running will help you maintain your leg turnover and stay on top of your running form/gait.
This can be as simple as including some strides or accelerations at the end of your run. To avoid the ice and snow you can find a well-plowed parking lot (preferably empty). All you need is a 50-60m section to get the job done. If you have access to a treadmill you can include some 15-20 second accelerations either at the end of an outdoor run or the end of a treadmill session.
Doing these accelerations is always best when your body is sufficiently warmed up especially when the air temperature is cold.