As we approach the end of July the statewide average temperature in Illinois is 70.6 degrees, which currently puts it in second place for the coldest July on record. I will post more on this at the end of the week.
Here is how the previous top 10 coldest July temperatures for Illinois looked and what happened in the following August (table below). In 8 out of the 10 cases, the following August was colder than average. However, two of those “colder” August’s were marginally so (1924 and 1996). The one spectacular reversal was in 1947, where August was 7.2 degrees above average after the 3rd coldest July. Therefore there is a historical tendency for cooler weather to prevail into August.
| Temperature (degrees F) | |||
| Year | July | August | August Departure |
| 2009 | 70.3 | 70.9 | -2.7 |
| 1924 | 71.1 | 73.2 | -0.4 |
| 1967 | 71.7 | 68.2 | -5.4 |
| 1971 | 71.9 | 71.6 | -2.0 |
| 1950 | 72.0 | 69.2 | -4.4 |
| 1915 | 72.2 | 66.9 | -6.7 |
| 1947 | 72.3 | 80.8 | 7.2 |
| 1904 | 72.4 | 69.8 | -3.8 |
| 1905 | 72.5 | 74.1 | 0.5 |
| 1996 | 72.6 | 73.5 | -0.1 |
We are using the 1981-2010 average for August (73.6 degrees) as the benchmark for this comparison. Statewide records go back to 1895.
The NWS forecasts are pointing towards a colder than average start to August, based on the latest 6-10 and 8-14 day forecasts.
