Precipitation
The statewide precipitation for May was 6.87 inches, 2.25 inches above the long-term average and the 12th wettest May on record. The wettest May on record was 1943 with 8.87 inches. By contrast, May 2012 was much drier with 2.50 inches for the entire month.
The monthly totals coming out of western Illinois are impressive. The heaviest amounts were contained in the area bound by St. Louis in the south, Springfield to the east, and Galesburg to the north. Radar-estimated precipitation amounts in those areas were as high as 12 to 15 inches. See map below. The largest monthly total at a single site so far was at Prairie City (McDonough County) with 14.12 inches.
On the other end of the scale, somewhat drier conditions prevailed in parts of Illinois north of Interstate 80. Amounts of 3 to 5 inches were common across the region. One of the lowest monthly totals was at Freeport (Stephenson County) with 3.19 inches.
The statewide precipitation for March-May (the traditional spring months) was 16.71 inches, 5.31 inches above the long-term average and the 5th wettest spring on record. The wettest spring on record was 1927 with 18.59 inches. By contrast, spring of 2012 was much drier with only 7.79 inches of precipitation.
The statewide precipitation for January-May (year to date) was 23.55 inches, 7.93 inches above the long-term average and the wettest January-May on record. By contrast, January-May of 2012 received only 10.87 inches of precipitation and was the 12th driest on record.
Temperature
The statewide average temperature for May was 63.6 degrees, just 1.1 degrees above the long-term average, which was pretty mundane compared to the precipitation totals. The statewide average temperature for spring (March-May) was 49.1 degrees and 2.9 degrees below the long-term average. The statewide average temperature for the year to date (January – May) was 41.2 degrees and 1.4 degrees below the long-term average.
Notes
The long-term average covers the period 1981-2010. The statewide records cover the period 1895 to 2013. These numbers are preliminary and will likely change as more data arrives.
