Don't wait until spring. Reseed now.
I have had several gardeners tell me that their cool season lawn (bluegrass, fescue or rye) is not looking very good. There are lots of areas where the turf is sparse. They want to know when in the spring is the best time to reseed the lawn.
Most gardeners are shocked when I tell them to reseed their lawn now and not wait till spring. They think that seed will freeze and not germinate, or the birds will eat all of it.
Of course the best time to reseed a cool season lawn in the heartland is in early fall. If you didn't get to it then, don't worry. The second best time to reseed is in winter, performing what is commonly called a dormant seeding.
If you want to reseed now, do it the same way you would reseed a lawn in early fall. Apply the seed to the surface of the lawn area. Also apply a starter fertilizer such as a 9-13-11 to the reseeded area.
Next run a verticutter over the seeded area to put the seed into the ground. This is needed to maximize germination percentage. You can do this even if the ground is slightly frozen.
The debris left after this process will act as a mulch to enhance moisture retention in the soil. If you have totally bare areas after the verticutter process, you may want to spread straw over them at the rate of one bale per 500 sq. ft.
The next item on the to do list is the toughest. Wait until the seed germinates before you apply more fertilizer or any herbicides. The germination process will be very slow because of the cold temperatures. So in this case patience is a virtue.
When the new grass seedlings are high enough to mow in the spring, go ahead and mow them. Mowing will encourage the new seedlings to mature. After you have mowed the new lawn area two times, you can apply post emergence herbicides for broadleaf weeds and a pre-emergent herbicide for crabgrass control. You can also apply spring time fertilizers to give the new seedlings the nutrition they need to start the growing season.
You just thought since the temperatures are dipping outside, you can't get that lawn going until next spring. Put on your coat and get going now so you can enjoy your lawn next spring without doing all of the work at that time.