Record Temperature Highs Outpacing Record Temperature Lows
This chart, from the University Corporation for Atmospheric Research, shows the number of daily record temperature highs and lows set each decade. As you can see, the ratio of highs to lows has shot up in the last 30 years. It's a fairly small sample size, but it's still telling: If temperatures were remaining static, the ratio of highs to lows should remain relatively the same.