Standardized Precipitation Index Table

Northwest Climate Division

Illinois, Climate Division 01

Precipitation Data Table

Time Scale in Months (As of the end of Nov. 2025)
1 2 3 4 5 6 7 8 9 10 11 12 15 18 24 30 36 48 60 72
Accumulated Precipitation (in.) 1.67 3.55 4.24 7.55 15.89 19.84 22.75 25.42 28.19 28.94 29.58 30.95 36.08 50.48 69.18 86.62 102.15 137.53 169.19 207.08
Accumulated Precipitation Departure from Normal (in.) -0.55 -1.33 -4.28 -4.73 -0.31 -0.65 -1.75 -2.43 -2.11 -2.77 -3.66 -4.16 -7.58 -5.13 -1.06 -4.13 -3.27 -3.05 -6.61 -3.96
Accumulated Precipitation Percent of Average 75 73 50 61 98 97 93 91 93 91 89 88 83 91 98 95 97 98 96 98
Accumulated Precipitation Percentile (non-exceedance) 40.9 27.7 5 7.4 50.2 47.4 38.8 34.4 37.2 33.1 27.2 24.7 12.1 26.2 46.5 34.9 38.8 41.2 32.4 40.6
Standardized Precipitation Index -0.23 -0.59 -1.64 -1.44 0 -0.06 -0.28 -0.4 -0.33 -0.44 -0.61 -0.68 -1.17 -0.64 -0.09 -0.39 -0.28 -0.22 -0.46 -0.24