The official National Weather Service forecast for Boulder — 46.2366°N, 112.1208°W, 0.9 miles from I-15.
| Jefferson County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 33 | 34 | 43 | 50 | 59 | 68 | 79 | 77 | 67 | 53 | 40 | 32 | 53 |
| Avg low °F | 15 | 15 | 21 | 27 | 35 | 42 | 49 | 47 | 40 | 31 | 21 | 15 | 30 |
| Precip in | 0.9 | 1.0 | 1.2 | 1.8 | 2.6 | 2.7 | 1.1 | 1.3 | 1.3 | 1.3 | 1.0 | 1.0 | 17.2 |
1996–2025 normals for Jefferson County — the climate division Boulder sits in. All-time county record high 94.9°F (2002-07-13); record low -36.5°F (1962-01-09). Source: NOAA / National Weather Service.