Summary

In Illinois, 2013 was slightly cooler and wetter than average. The first half of the year was the wettest on record, which led to flooding and planting delays across the state. This was followed by a rapid onset of drought in parts of the state in late summer and fall. The year finished on a cold note with below-average temperatures in November and December.

By the Numbers

Based on the latest data, the statewide average temperature for 2013 in Illinois was 50.8 degrees (1.4 degrees below the 1981-2010 average). That is much cooler than 2012 when the statewide average temperature was 55.6 degrees.

The statewide average precipitation for 2013 in Illinois was 43.77 inches (3.58 inches above the 1981-2010 average). The precipitation for the two halves of 2013 were very different. The precipitation for the first 6 months of 2013 totaled 28.96 inches and was 9.13 inches above average and the wettest January-June on record. The precipitation in the following 6 months of 2013 totaled 14.81 inches and was 5.56 inches below average and the 19th driest July-December on record.

By the way, the 2013 annual statewide average precipitation of 43.77 inches was 12.94 inches wetter than 2012 when we received only 30.83 inches across the state.

Annual Precipitation Maps

The annual precipitation for 2013 and its percent of average across the state are shown in the following two maps (click to enlarge). The largest precipitation totals were in the far southern region of the state (greater than 50 inches) and the smallest totals were in parts of central and northwestern Illinois (less than 35 inches). A few of the dry spots were down to 90 percent of the average annual precipitation. While that was modest compared to the drought of 2012, those areas were showing some lingering signs of drought in stream flows, lake levels, and groundwater supplies even in late December.

Monthly Temperature and Precipitation

Here is the breakdown of temperatures and precipitation by month for 2013 with comparisons to the 1981-2010 average. As the first graph and table show, January was warmer than average, while March was much colder an average due to the late start and ending of “winter”. In fact, winter weather didn’t arrive until late February and lingered on into early April. Summer temperatures was slightly cooler than average as the growing season finished off with a warmer than average September. November and December were noteworthy for being exceptionally cold and combined they were the 8th coldest November and December on record.

As mentioned earlier, the precipitation for 2013 was memorable for the wet spring and early summer, followed by dry weather starting in July. The heart of the wet weather was in April, May, and June. This was followed by three months of significant dryness (July-September). The second graph and table shows the month by month precipitation.

Note: here the statistics for 2013 are compared to the 30-year average, or normal, for 1981-2010.  

Temperature (F)
Year	Month	Temp	Normal	Depart
2013	Jan	28.9	24.6	4.3
2013	Feb	29.9	30.1	-0.2
2013	Mar	34.1	40.7	-6.6
2013	Apr	49.7	51.7	-2.0
2013	May	63.6	62.4	1.2
2013	Jun	71.3	71.6	-0.3
2013	Jul	72.9	75.4	-2.5
2013	Aug	72.3	73.2	-0.9
2013	Sep	68.4	65.8	2.6
2013	Oct	54.3	54.1	0.2
2013	Nov	38.3	41.5	-3.2
2013	Dec	25.5	29.9	-4.4
Precipitation  (inches)
Year	Month	Prcp	Normal	Depart
2013	Jan	3.87	2.12	1.75
2013	Feb	2.82	2.11	0.71
2013	Mar	2.74	2.98	-0.24
2013	Apr	7.10	3.80	3.30
2013	May	7.02	4.62	2.40
2013	Jun	5.41	4.20	1.21
2013	Jul	3.14	4.05	-0.91
2013	Aug	1.63	3.60	-1.97
2013	Sep	1.73	3.24	-1.51
2013	Oct	3.14	3.26	-0.12
2013	Nov	2.68	3.47	-0.79
2013	Dec	2.50	2.74	-0.24