Not quite sure what you're asking, but fescue and most grasses should be allowed to get longer in the heat of summer. Deep and infrequent watering really helps the lawn make it through periods of heat and drought. The exceptions to the tall grass in summer are bermuda and centipede. Those should be short all year.

I started out the first mow of the season at 3.5" and currently at 3.75" mowing twice weekly. As the temps start to rise I continue raising the cut until I eventually hit about 4.5". As soon as things turn dry I stop mowing and generally growth stops with it. My lawn is 1/2 acre so watering is really out of the question.

If you can water your lawn throughout the heat of summer you will most likely still have to mow but the frequency should slow down. Since I can't water my lawn it will go dormant and turn brown after several weeks of no rain and high temps. As soon as we get rain it will green back up. My mower will go up to a 5.5" cut so when it's hot and dry I just don't mow. The lawn does get a little shaggy but there's no good reason to stress an already stressed lawn by mowing. The bad news is we only get about 5 months of prime fescue season here in NC. March, April and May then October, November and part of December.

Well i went out of town for a week and 2 days about 3 weeks ago. I mowed my lawn down to 3.5 inches where i keep it in the fall. When i returned home it was at 6.5 inches. I was just wondering if i could just let it go wild in the summer that is however much it decides to grow with out cutting it until the heat dies down. So from what you both posted above i assume i should be ok and try to stay off of it invthe heat of the summer and only mow if i really have too

I haven't tried it with northern grasses, but with St Augustine it stops growing at 32 inches tall. Here's a picture of my dog sitting in it.

I did not have to water that grass for over 2 years even through a
pretty bad drought. Deep roots solve most all lawn issues, but getting
the roots deep means growing the grass tall.

Nice