The official National Weather Service forecast for Hartland — 43.105°N, 88.342°W, 12.5 miles from I-41. Forecasts here are written by NWS MKX, this county’s forecast office.
| Waukesha County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 28 | 32 | 44 | 57 | 68 | 78 | 82 | 80 | 74 | 61 | 46 | 34 | 57 |
| Avg low °F | 13 | 16 | 25 | 35 | 46 | 56 | 60 | 59 | 52 | 40 | 30 | 19 | 38 |
| Precip in | 1.6 | 1.6 | 2.2 | 3.6 | 4.2 | 4.8 | 3.7 | 3.9 | 3.4 | 2.8 | 2.0 | 1.9 | 35.7 |
1996–2025 normals for Waukesha County — the climate division Hartland sits in. All-time county record high 103.0°F (2012-07-06); record low -29.2°F (1951-01-30). Source: NOAA / National Weather Service.