The official National Weather Service forecast for Merrimac — 43.3733°N, 89.6235°W, 8.2 miles from I-39. Forecasts here are written by NWS MKX, this county’s forecast office.
| Sauk County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 27 | 32 | 44 | 57 | 69 | 79 | 83 | 80 | 74 | 60 | 46 | 32 | 57 |
| Avg low °F | 10 | 13 | 24 | 34 | 46 | 56 | 60 | 58 | 50 | 38 | 28 | 16 | 36 |
| Precip in | 1.2 | 1.3 | 2.3 | 3.7 | 4.3 | 5.4 | 4.1 | 4.3 | 3.2 | 2.7 | 2.0 | 1.7 | 36.2 |
1996–2025 normals for Sauk County — the climate division Merrimac sits in. All-time county record high 102.2°F (2012-07-07); record low -46.0°F (1951-01-30). Source: NOAA / National Weather Service.