The official National Weather Service forecast for Waterloo — 41.432°N, 85.02°W, 1.9 miles from I-69. Forecasts here are written by NWS IWX, this county’s forecast office.
| DeKalb County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 32 | 36 | 48 | 60 | 71 | 80 | 83 | 81 | 76 | 63 | 49 | 37 | 60 |
| Avg low °F | 18 | 20 | 28 | 38 | 49 | 59 | 61 | 60 | 53 | 42 | 32 | 23 | 40 |
| Precip in | 2.4 | 2.1 | 2.6 | 3.5 | 4.6 | 3.9 | 3.8 | 3.6 | 2.9 | 2.9 | 2.7 | 2.5 | 37.5 |
1996–2025 normals for DeKalb County — the climate division Waterloo sits in. All-time county record high 104.6°F (2012-06-29); record low -21.5°F (1994-01-19). Source: NOAA / National Weather Service.