Last Frost Date Great Falls: Frost Dates, Late Frost Risk & Growing Season

When is the last spring frost and the first autumn frost in Great Falls? Frost dates from 30 years of data, the risk of late frost, frost-free days and planting dates.

The frost season in Great Falls

Last frost (average): May 19
In 1 year out of 10 it still freezes on June 7.
First frost: September 23
Frost-free season: 127 days
Frost after 15 May: in 53 % of years

Frost days per month in Great Falls

January: 30.3 · -9 °C
February: 27.7 · -9 °C
March: 28.5 · -5 °C
April: 19.4 · -1 °C
May: 5.9 · 4 °C
June: 0.2 · 8 °C
July: 0 · 11 °C
August: 0.1 · 10 °C
September: 2.2 · 6 °C
October: 14.6 · 0 °C
November: 25.4 · -5 °C
December: 30.2 · -9 °C

Matched to the average lows of a weather station 6 km away – accurate to about ±1–2 weeks.
Daily minimum temperatures 2 m above ground over 30 years (1991–2020), NASA POWER; station data: Deutscher Wetterdienst (CC BY 4.0). Ground frost can form while the air at 2 m is still +2 to +3 °C.