For a while TreeHugger has been writing about how new record highs are outpacing new record lows in the US. It's one more predicted effect of rising global temperatures, and only likely to get worse.
Historically the expectation is roughly a 1:1 ratio between new record highs and lows. On a decadal basis the ratio may skew one way or the other a bit, as it did throughout the 20th century. However since the 1980s research has shown that this ratio is shifting solidly towards more record heat. In the first ten years of the 21st century the ratio was 2.04:1, heat to cold.In recent years and months it's even more dramatic though. June 2011 for example had a ratio of 11:1 record heat. That's just one month. For all of 2011 the ratio ended up being about 2.7:1, slightly higher than the 2.33:1 ratio for 2010.
But through the first six months of 2012 in the contiguous US, the ratio was 9:1, as Climate Central points out. That's still a short time period that will likely be balanced out a good bit over the entire year, but a sign of things to come.
At current emissions trajectories by 2050 the ratio of new record highs to lows will be 20:1, by 2100 it may be as high as 50:1.