As we move past mid-July, the climatologically warmest day of the year in Madison (i.e. the day with the highest average high temperature) is in our immediate wake.
Every 10 years the 30-year climatology is updated in the following way: In 1972, we used the 1941-1970 average as climatology. By 1982 we were using the 1951-1980 average as climatology. Currently, we are using the 1981-2010 average as climatology.
Though the particular averaging period has changed over the past four decades, the average warmest day of the year has consistently fallen around July 15.
This summer we haven’t had much in the way of heat, recording only two days with a temperature at or above 90 degrees (June 9 at 90 and Friday at 91).
June was just 0.1 degrees above normal — mostly as a consequence of warmer-than-normal overnight low temperatures — and July has averaged 6.2 degrees cooler than normal through the first third of the month.
The coolness thus far does not mean that the rest of the summer will remain moderate, as only 12 of the last 30 summers have recorded more days at or above 90 degrees before July 15 than after it. In fact, in the 13-year period from 1985-97, nine summers recorded the bulk of their 90-degree days before mid-July. From 1998 to 2014, only three such summers have occurred (2007, ’08, and ’12). So, front-loading 90-degree days in the summer has become increasingly rare this century. We’ll see what 2015 brings in the next few weeks.