Soil temperature is really the driving factor.
The roots of your cool-season grass, like blue fescue begin to absorb nutrients and moisture as soon as the ground reaches 55 to 65 degrees Fahrenheit. In response, the grass blades soon follow with prolific growth, especially when the air temperature ranges between 60 and 75 degrees Fahrenheit.
In contrast, warm-season grasses, like bermuda grass (Cynodon dactylon) respond to soil temperatures above 70 degrees Fahrenheit for normal spring growth. One way to verify this prime temperature threshold is comparing night and daytime air temperatures. For example, daytime temperatures above 80 degrees Fahrenheit, and nighttime values of 65 degrees Fahrenheit, often indicate a perfect time for warm-season grass growth.
Source: The Temperature That Grass Starts to Grow After Winter by Amy Rodriguez, SFGATE
Check out today’s soil temperature map (March 11, 2015)
As you can see the soil temperature is quickly approaching the 55 to 65 mark for cool-season grasses and warm-season grasses.
Picture Source Flickr – Diane Hammond