Thank you for reaching out to ask2.extension.

No matter which kind of grass, you want to fertilize your lawn while it's actively growing. For cool-season grasses, that means in spring and/or fall. Warm-season grasses respond best when fertilized in late spring and/or early summer.

If your lawn goes dormant in the winter, you shouldn't fertilize it after September 1.  Cool-season grasses, also known as "northern grasses", grow best in areas with cold winters and hot summers, and are hardy in those climates. They grow most actively in the spring and fall when temperatures are between 60-75°F, and their growth slows down in the summer heat. 

You should avoid fertilizing during periods of extreme heat or drought, and you shouldn't apply fertilizer to wet grass because it can clump together and distribute unevenly.

I would suggest you wait now until later in August, unless your area keeps getting regular rain, or you plan to water.