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)
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.
The Midwestern Regional Climate Center, located at the Illinois State Water Survey, recently released a new tornado tracking tool. You can choose the range of years, and the tornado intensity (EF scale), as well as zoom in for more details (screen shot below). BTW, the tool covers the entire US, not just the Midwest. It is another great tool developed by our talented GIS expert Zoe.
Speaking of tornadoes, here is the monthly tally of tornadoes in Illinois for 2014. Half of our tornadoes this year occurred in February while March through July have been very quiet.
That is about the opposite of the tornado climatology for Illinois, which shows that winter months are typically much quieter than the spring and early summer months.
Despite the recent short-lived warm spell that ends today, Illinois is on track to be one of the coolest July’s on record. The statewide average temperature from July 1-21, 2014, was 70.4 degrees. That is just 0.1 degrees off from the coolest July on record – set in 2009 with a temperature of 70.3 degrees. Of course we are only two-thirds of the way through the month but the NWS forecast for the rest of July is interesting (shown below).
July 2009: 70.3 degrees
July 2014: 70.4 degrees (as of July 22)
July 1924: 71.1 degrees
July 1967: 71.7 degrees
July 1971: 71.9 degrees
July 1950: 72.0 degrees
July 1915: 72.2 degrees
July 1947: 72.3 degrees
July 1904: 72.4 degrees
July 1905: 72.5 degrees
As this map shows, the cooler-than-average temperatures are not confined to Illinois, but is spread across the Midwest (shades of green show the degree of cooling compared to the 1981-2010 average).
With nine more days to go, the NWS forecasts indicate that temperatures are likely to be below average for the rest of the month. Here are snap shots of the NWS 6-10 and 8-14 day temperature forecasts, as of July 22, showing the large area across the central US expected to have below-average temperatures. Meanwhile the West Coast will be facing warmer-than-average conditions in a summer shaping up to be hot.
If this forecast holds true, this July could end up in the list of top 10 coolest July’s on record.
The NWS Climate Prediction Center released their latest outlook for August and beyond. In the figure below, the top row are the temperature and precipitation outlooks for August. The second row is for August – October. Click to enlarge.
For August, northern Illinois has an increased chance of below-average temperatures, along with Iowa, Wisconsin, Minnesota, and the Dakotas. Precipitation in August has equal chances (EC) of being above, below, or near-average.
For August-October, almost all of Illinois has an increased chance of below-average temperatures. Precipitation during this period has equal chances of being above, below, or near-average.
So far, July is shaping up to be both cooler and wetter than average. Through July 16, the statewide average temperature was 70.9 degrees, 5 degrees below average. Statewide precipitation was 2.9 inches, 54 percent above average.