Precipitation. May precipitation at the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC) totaled 4.76 inches - surpassing the total accumulated during the four previous months combined (Table) and totaling very close to the 30-year normal. Unlike other areas of the state and country that were deluged with several inches of rain at a time, the rain at the NWIARDC arrived on 18 of the month's 31 days (Figure).
2015 PRECIPITATION (in inches)
| Since January 1 | ||||
| Month | Monthly Total | Monthly departure from average | Total accumulation | Total departure |
| January | 1.32 | -0.20 | 1.32 | -0.20 |
| February | 1.28 | -0.26 | 2.60 | -0.46 |
| March | 0.83 | -1.70 | 3.43 | -2.16 |
| April | 1.21 | -2.67 | 4.64 | -4.83 |
| May | 4.76 | +0.01 | ||
Temperature. The average daily high and low air temperatures remained close to the 30-year "normals" for the month of May (Figure).
May 2015 WEATHER
| Soil Temperature | |||||
| Air Temp | 2" (Bare) | 4" (Bare) | 4" (Sod) | ||
| (°F) | Growing Degree Days | -------------------(°F)-------------------- | |||
| Monthly average high | 74 | Monthly total: 470.5 | 73 | 74 | 65 |
| Monthly average low | 53 | 58 | 57 | 61 | |
| Observed high (date) | 84 (4) | 24 (29) | 79 (5) | 80 (23) | 71 (27) |
| Observed low (date) | 32 (1) | 0 (21) | 47 (1,21,23) | 50 (1) | |
Reference. Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2015). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495.