As a form of self-preservation, grass becomes dormant after a stretch of hot, dry weather. While a yellow lawn may not be attractive, the grass is protecting itself and will usually recover when the rains return.
Here are some tips from a number of lawn care experts to help that recovery:
Heat- and drought-stressed grass will recover if kept healthy and generally maintained.
Give the lawn 1 to 2" of water once a week. As a rule of thumb: Running sprinklers for one hour provides 1 inch of water to the area it covers, two inches in two hours, etc.
Be careful not to overwater. Overwatering produces shallow roots, making it more vulnerable to heat or pests.
The best time to water is early morning, because less water is lost to evaporation.
The worst time to water is in the evening, when too little water is lost to evaporation. Diseases are more likely to develop in a wet lawn.
Raise that mower and let grass blades grow to 3" in height. Taller blades have deeper roots. Also, higher blades provide more shade for soil, and shade also has the benefit of stunting the growth of weeds.
Maintain the lawn, watching for weeds. Weed growth can increase thanks to the heat. Weeds tend to be more resilient.