Normally you cut it longer in the summer, but not so long that it will be wet all day and night. If you are normally at 2.5, then 3 to 3.5 is fine. It will reduce the stress on the grass, and deplete less of it's reserves. At high temps top growth slows down considerably, so you will probably find you won't need to mow as often.

>" At high temps top growth slows down considerably, so you will probably find you won't need to mow as often."

+1

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Part of your contradictory advice may be as simple as folks from all over the nation with different sorts of grasses and environments....

MY crazy hot for extended periods of time is DIFFERENT than yours is.... We have already had 5 weeks >90F this year.... Maybe 5 days over 100 now...

Different grass needs different culture... I have mostly old pasture type Tall Fescue -- it doesn't do well cut short below 4"... Fine fescue is a different story... It doesn't do well at 3.5" tall.... It flops over and mats down.

My own limited experience with Cool season grasses...

I have noticed my cool season grasses get *VERY* unhappy when I cut them when they are already heavily stressed.... So... If they have obviously stopped growing and are looking dull and silvery or are heading towards brown... Don't mow.... or if you do -- be prepared to baby it for a few days to a week afterwards.... My Fescue gets *Very* thirsty and droughty looking the day after mowing when it's been 90+ outside for a few weeks.... It takes 3-4 days to recover, and then it is OK for a while again..

My own policy is now that I won't mow grass when it's heavily stressed unless I just can't help it... Or... unless I am trying to kill it off...

Thanks

John