Based on preliminary data, July was both cooler and wetter than average for Illinois.
The statewide average temperature in July was 74.4 degrees, 0.9 degrees below average. That is not nearly as cool as our record-setting July 2014 when the average temperature was only 70.3 degrees (5.0 degrees below average). On the extreme other end, July 2012 was 81.8 degrees (6.5 degrees above average and the 2nd warmest on record). More on July temperature trends in another post.
July Precipitation. Click to enlarge.
January 2015 in Illinois was cooler and drier than average. The statewide temperature was 25.4 degrees, 1 degree below average and the 53rd coldest on record. However, it was not nearly as cold as last January when the average temperature was 19.3 degrees and ranked as the 16th coldest on record.
The statewide average precipitation for January 2015 was 1.53 inches, 0.5 inches below average. Because of dry weather in November, December, and January, the US Drought Monitor introduced “D0” in northern and western Illinois. As I explained in an earlier post, this is not a great concern yet because of the low demand for water in winter but we are watching the situation.
Snowfall ranged from less than an inch in the far south to 10 to 15 inches north of Interstate 80 (first map). That results in above-average snowfall in the northern half of the state and below-average for the southern half (second map). However, this was far less snow than January 2014 (last map) when most of the state was covered with 10 to 25 inches of snow. Continue reading
I will admit it – ever since I was a kid I have been fascinated/obsessed with maps. It is probably why I ended up in a career in climatology since we use maps all the time.
Here are maps from the National Climatic Data Center showing how cool July was across the Midwest. The regions are called “climate divisions” and there are nine of them in Illinois. The ones in the darkest blue had their coolest July on record, with records going back to 1895. Click on the map for a larger version which shows the numbers more clearly.
You can read more about what happened in the US in July.
July Temperature Ranking. Click to enlarge. Source National Climatic Data Center.
And here are the temperature departures from the 1981-2010 average.
July Temperature Departures. Click to enlarge. Source National Climatic Data Center.
Here is the US map for July, showing that while the Midwest was cool, the western US was experiencing record warmth.
Click to enlarge. Source National Climatic Data Center
This temperature pattern across the United States is the result of a ridge of high pressure over the western US and a trough of low pressure over the central US throughout most of July.
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.
What a difference in temperature between July 2012 and 2013. Last year we were in the midst of a full-blown drought and heat wave with temperatures routinely in the 90s and low 100s. The statewide average temperature for July 2012 was 81.8°F (6.5°F above the 1981-2010 average) and the second warmest July in Illinois behind the record of 83.1°F in 1936.
This July has had its hot and humid moments, but for the most part has been mild overall in Illinois. The statewide average temperature for July 2013, as of July 29, is 73.6°F ( 1.7°F below the 1981-2010 average) and the 23rd coolest July on record based on preliminary data.
The cool July weather was confined to the central and southeastern US. Meanwhile, both the western and northeastern US have experienced warmer than average temperatures this month.
Figures. July 2013 compared to July 2012 in terms of temperature departures from average.
Temperature Departures for this July through the 29th. Cool weather prevails across much of the lower Midwest.
July 2012 – toasty indeed.