WEATHER · CLIMATE NORMALS · 1991–2020
Helena Climate — Averages by Month
What the weather in Helena, USaverages across a standard 30-year period. Each month's figure is the 1991–2020 mean temperature and total rainfall from the ERA5 reanalysis — the long-run normal a place settles around, not a forecast for any particular day.
Month-by-month normals
| Month | Avg temperature | Avg rainfall |
|---|---|---|
| January | -6.9 °C · coldest | 29.5 mm |
| February | -5.8 °C | 30.1 mm |
| March | -1.2 °C | 42.8 mm |
| April | 3.2 °C | 67.7 mm |
| May | 8.8 °C | 86.0 mm |
| June | 13.3 °C | 101.4 mm · wettest |
| July | 18.2 °C · warmest | 46.9 mm |
| August | 17.7 °C | 39.5 mm |
| September | 12.4 °C | 43.8 mm |
| October | 5.1 °C | 42.4 mm |
| November | -1.9 °C | 35.1 mm |
| December | -6.9 °C | 32.8 mm |
How to read these numbers
These are reanalysis normals, not readings from a single weather station. They come from the ERA5 0.25° (~25 km) global reanalysis grid, sampled at the grid cell nearest Helena — centred at 46.50°N, 112.00°W. A reanalysis blends observations with a physics model onto an even grid, so a coastal or mountain city's cell can read a little cooler, warmer, wetter or drier than the city centre itself. The month-to-month shape — when it's hot, when it rains — is what these normals capture best.
“Normal” means the 1991–2020 average, the current World Meteorological Organization standard period. A normal is what a place tends toward over decades — any single day, month or year can and will depart from it.