This has been explained as a consequence of stronger warming trends in the Arctic, where the cold air originates. (climateprediction.net)
Finds that, in general, the indices based on minimum temperature show stronger warming trends than indices calculated from maximum temperature (climatesignals.org)
We can see from Figure 6, that the Buenos Aires station record implies that there has been a very strong warming trend since the early 20th century. (globalwarmingsolved.com)