Montana frost dates: Last spring and first autumn frost at every NOAA station, 1991-2020
Across Montana's 216 NOAA stations with frost dates, the median last spring frost (32°F) runs from April 30 in Norris to June 18 in Tizer Gardens; for half of its places it comes after May 18.
- Typical last spring frost
- May 18median of 121 places
- Typical first autumn frost
- September 21median of 121 places
- Earliest last frost
- April 30Norris
- Latest last frost
- June 18Tizer Gardens
When is the last frost in Montana, town by town?
Each date is NOAA's: "after May 18 in half of years" means the last 32°F night of spring came after May 18 in half of the years 1991-2020. By the 1-in-10 date, the last frost has passed in nine years out of ten.
Find your town in the list, or look up a ZIP code for the stations nearest it.
| Place or station | Last frost (median) | 1 in 10 after | First frost (median) | 1 in 10 before | Growing season | Zone |
|---|---|---|---|---|---|---|
| NorrisNorris Madison Power House | April 30 | May 14 | October 10 | September 27 | 162 days | 6a |
| Bigfork (13 mi S) | May 1 | May 16 | October 15 | September 30 | 165 days | 6b |
| Glasgow #2 | May 3 | May 15 | October 1 | September 19 | 151 days | – |
| Glendive | May 3 | May 16 | October 4 | September 22 | 153 days | 4a |
| BillingsBillings International Airport | May 4 | May 18 | October 7 | September 26 | 156 days | 5a |
| Billings Weather Office | May 5 | May 21 | October 3 | September 20 | 149 days | 5a |
| Mosby (4 mi ENE) | May 5 | May 26 | October 4 | September 22 | 151 days | – |
| GlasgowGlasgow International Airport | May 6 | May 18 | September 30 | September 17 | 145 days | 4a |
| Great Falls 16ST | May 6 | May 19 | October 1 | September 17 | 147 days | – |
| Missoula 6 NW Weather Office | May 6 | May 19 | October 4 | September 23 | 151 days | – |
| Highwood7 mi NE | May 7 | May 21 | October 2 | September 19 | 149 days | – |
| Malta (7 mi E) | May 7 | May 21 | September 28 | September 14 | 143 days | – |
| Thompson FallsThompson Falls Powerhouse | May 7 | May 19 | October 4 | September 21 | 150 days | 6b |
| Yellowtail Dam | May 7 | May 24 | October 5 | September 20 | 151 days | 5a |
| Fort PeckFort Peck Power Plant | May 8 | May 20 | October 1 | September 18 | 145 days | 4b |
| Miles CityMiles City F Wiley Field | May 8 | May 21 | September 30 | September 17 | 144 days | 4b |
| Wolf Point station | May 8 | May 20 | September 28 | September 15 | 143 days | – |
| Forsyth | May 9 | May 21 | September 29 | September 16 | 142 days | 4b |
| HelenaHelena Regional Airport | May 9 | May 25 | September 30 | September 17 | 142 days | 5a |
| Hungry HorseHungry Horse Dam | May 9 | May 30 | October 1 | September 13 | 141 days | 5b |
| Trident | May 9 | May 24 | September 27 | September 12 | 139 days | 4b |
| Billings Water Treatment Plant | May 10 | May 24 | October 1 | September 19 | 142 days | 5a |
| Hysham | May 10 | May 22 | September 29 | September 15 | 141 days | 4b |
| Libby | May 10 | May 26 | September 26 | September 11 | 137 days | – |
| Malta | May 10 | May 22 | September 29 | September 17 | 139 days | – |
| Melstone | May 10 | May 23 | September 29 | September 14 | 141 days | 4b |
| Missoula (2 mi NE) | May 10 | May 28 | October 1 | September 16 | 143 days | – |
| Polson | May 10 | May 26 | October 5 | September 22 | 147 days | 6a |
| EurekaEureka Ranger Station | May 11 | May 25 | September 27 | September 10 | 138 days | 5a |
| Libby Dam (Base) | May 11 | May 27 | October 1 | September 14 | 142 days | 6b |
| Sidney | May 11 | May 25 | September 27 | September 13 | 137 days | 4a |
| Baker station | May 12 | May 27 | September 26 | September 11 | 135 days | – |
| Creston | May 12 | May 26 | September 25 | September 9 | 134 days | 5b |
| Great Falls Weather Office | May 12 | May 27 | September 28 | September 14 | 138 days | – |
| HuntleyHuntley Experiment Station | May 12 | May 26 | September 25 | September 13 | 136 days | 4a |
| NashuaNashua #2 | May 12 | May 26 | September 24 | September 12 | 134 days | – |
| Sand Creek | May 12 | May 27 | September 27 | September 14 | 136 days | – |
| Savage | May 12 | May 26 | September 25 | September 12 | 135 days | 4a |
| St. IgnatiusSaint Ignatius | May 12 | June 1 | October 2 | September 19 | 142 days | – |
| Terry | May 12 | May 25 | September 28 | September 13 | 137 days | 4a |
| Brady 27 ENE (The Knees) | May 13 | May 29 | September 29 | September 16 | 137 days | – |
| Fairfield | May 13 | June 1 | September 27 | September 14 | 135 days | 4b |
| Hardin | May 13 | May 26 | September 29 | September 14 | 135 days | 4b |
| Powderville (8 mi NNE) | May 13 | May 31 | September 25 | September 6 | 132 days | 4a |
| St. MarieSt Marie | May 13 | May 26 | September 27 | September 13 | 134 days | 4a |
| Wolf Point (34 mi NE) | May 13 | May 25 | September 28 | September 14 | 137 days | – |
| Biddle8 mi SW | May 14 | May 27 | September 28 | September 13 | 134 days | 5a |
| Big Timber | May 14 | May 27 | September 26 | September 10 | 133 days | 4b |
| Bridger2 mi N | May 14 | May 30 | September 24 | September 7 | 129 days | 5a |
| Chinook | May 14 | May 27 | September 23 | September 11 | 130 days | 3b |
| Geraldine | May 14 | May 28 | September 26 | September 13 | 134 days | 4b |
| Lewistown station | May 14 | May 27 | September 28 | September 14 | 135 days | – |
| Roy8 mi NE | May 14 | May 29 | September 24 | September 12 | 134 days | – |
| Troy | May 14 | May 31 | September 25 | September 9 | 132 days | 6b |
| Colstrip | May 15 | May 28 | September 30 | September 15 | 138 days | 4b |
| Fort Assiniboine | May 15 | May 28 | September 24 | September 8 | 130 days | 4a |
| Fort Benton | May 15 | May 30 | September 22 | September 7 | 129 days | 4a |
| HavreHavre Airport Asos | May 15 | May 27 | September 23 | September 11 | 129 days | 3b |
| Hinsdale4 mi SW | May 15 | May 30 | September 26 | September 12 | 132 days | – |
| Rock Springs | May 15 | May 27 | September 25 | September 10 | 132 days | 4b |
| SKQ Dam | May 15 | June 1 | September 28 | September 13 | 134 days | 6b |
| Saco1 mi NNW | May 15 | May 26 | September 23 | September 11 | 130 days | 3b |
| Sweetgrass | May 15 | May 28 | September 25 | September 11 | 132 days | – |
| BakerBaker Municipal Airport | May 16 | May 29 | September 26 | September 11 | 132 days | 4a |
| Broadus | May 16 | May 29 | September 28 | September 13 | 135 days | 4b |
| Bynum4 mi SSE | May 16 | May 28 | September 27 | September 16 | 133 days | – |
| Flatwillow (4 mi ENE) | May 16 | May 31 | September 28 | September 15 | 132 days | 4b |
| Fort Belknap (2 mi SW) | May 16 | May 28 | September 22 | September 10 | 128 days | – |
| Fortine1 mi N | May 16 | June 3 | September 18 | September 1 | 121 days | – |
| Harlem | May 16 | May 31 | September 21 | September 8 | 125 days | 3b |
| Malta (35 mi S) | May 16 | May 29 | September 23 | September 10 | 128 days | 3b |
| Medicine Lake3 mi SE | May 16 | May 30 | September 18 | September 7 | 125 days | – |
| MissoulaMissoula International Airport | May 16 | June 1 | September 26 | September 12 | 130 days | 5b |
| Tiber Dam | May 16 | May 30 | September 23 | September 9 | 129 days | – |
| Vida6 mi NE | May 16 | May 31 | September 22 | September 10 | 129 days | – |
| Whitefish | May 16 | June 6 | September 25 | September 8 | 129 days | 5b |
| Winifred | May 16 | May 30 | September 23 | September 9 | 127 days | 4a |
| Wolf PointWolf Point International Airport | May 16 | May 29 | September 20 | September 7 | 125 days | – |
| Big Sandy | May 17 | June 4 | September 25 | September 12 | 128 days | – |
| Circle | May 17 | May 31 | September 22 | September 7 | 126 days | 3b |
| Moorhead (9 mi NE) | May 17 | May 31 | September 22 | September 7 | 126 days | 4b |
| Ridgeway (1 mi S) | May 17 | June 1 | September 22 | September 5 | 127 days | 4a |
| Ryegate | May 17 | May 30 | September 23 | September 10 | 127 days | – |
| Sunburst8 mi E | May 17 | May 31 | September 25 | September 9 | 129 days | – |
| Superior | May 17 | June 8 | September 23 | September 6 | 125 days | 6a |
| Swan Lake | May 17 | June 4 | September 19 | September 4 | 121 days | 5b |
| Valier | May 17 | May 31 | September 24 | September 11 | 129 days | 4b |
| Alberton | May 18 | June 6 | September 25 | September 7 | 126 days | 6a |
| Brandenberg | May 18 | May 30 | September 22 | September 8 | 126 days | 4a |
| Carlyle (13 mi NW) | May 18 | May 31 | September 29 | September 13 | 134 days | 4b |
| JordanJordan Airport | May 18 | May 31 | September 20 | September 8 | 123 days | 3b |
| Valentine | May 18 | May 31 | September 21 | September 7 | 124 days | 3b |
| West Glacier | May 18 | June 4 | September 20 | September 3 | 124 days | 5a |
| Westby | May 18 | May 30 | September 21 | September 7 | 125 days | 3b |
| Zortman | May 18 | June 1 | September 23 | September 7 | 126 days | – |
| Augusta | May 19 | May 31 | September 21 | September 4 | 125 days | – |
| Great FallsGreat Falls Airport | May 19 | June 2 | September 24 | September 9 | 126 days | 4b |
| Holter Dam | May 19 | June 8 | September 24 | September 6 | 124 days | 4b |
| Lewistown (11 mi ESE) | May 19 | June 1 | September 25 | September 11 | 128 days | – |
| Livingston (12 mi S) | May 19 | June 11 | September 25 | September 7 | 125 days | 5a |
| Port Of Morgan | May 19 | June 2 | September 22 | September 9 | 124 days | 4a |
| Raymond Border Station | May 19 | June 1 | September 23 | September 11 | 125 days | 4a |
| Townsend3 mi SE | May 19 | June 2 | September 19 | September 5 | 122 days | 4b |
| Turner (11 mi N) | May 19 | June 1 | September 21 | September 8 | 124 days | 4a |
| Bredette | May 20 | June 1 | September 21 | September 6 | 122 days | 4a |
| Brockway3 mi WSW | May 20 | June 5 | September 19 | September 4 | 121 days | 4a |
| Choteau (8 mi NE) | May 20 | June 4 | September 22 | September 8 | 123 days | – |
| Conrad | May 20 | June 3 | September 19 | September 4 | 119 days | 4a |
| Ekalaka | May 20 | June 1 | September 23 | September 7 | 126 days | 4b |
| Grass Range | May 20 | June 6 | September 24 | September 11 | 126 days | 4b |
| Heron2 mi NW | May 20 | June 5 | September 20 | September 1 | 119 days | 6a |
| Lindbergh Lake | May 20 | June 7 | September 22 | September 5 | 120 days | 5a |
| Loma | May 20 | June 3 | September 19 | September 4 | 120 days | 3b |
| Mildred (5 mi N) | May 20 | June 2 | September 22 | September 7 | 124 days | 4a |
| Roundup | May 20 | June 2 | September 21 | September 5 | 124 days | 4b |
| Trout CreekTrout Creek Ranger Station | May 20 | June 9 | September 21 | September 2 | 122 days | 6a |
| Cascade5 mi S | May 21 | June 6 | September 19 | September 2 | 120 days | – |
| Culbertson | May 21 | June 3 | September 20 | September 6 | 120 days | 3b |
| Gardiner | May 21 | June 9 | September 27 | September 12 | 128 days | 5b |
| Hamilton | May 21 | June 6 | September 22 | September 6 | 122 days | 6a |
| Ingomar (9 mi E) | May 21 | June 4 | September 19 | September 6 | 120 days | 3b |
| Joplin | May 21 | June 6 | September 19 | September 3 | 119 days | 4a |
| Jordan station | May 21 | June 2 | September 18 | September 4 | 118 days | – |
| Plevna | May 21 | June 4 | September 20 | September 5 | 121 days | 4a |
| Rogers Pass (9 mi NNE) | May 21 | June 8 | September 15 | August 30 | 115 days | 4a |
| Wyola1 mi SW | May 21 | June 2 | September 17 | September 5 | 117 days | – |
| Mizpah (4 mi NNW) | May 22 | June 7 | September 15 | September 2 | 117 days | 3b |
| Pompeys Pillar (15 mi N) | May 22 | June 7 | September 22 | September 7 | 121 days | 4a |
| Raynesford2 mi NNW | May 22 | June 9 | September 23 | September 7 | 123 days | 4b |
| Roundup (15 mi SW) | May 22 | June 4 | September 15 | August 31 | 114 days | – |
| Stevensville | May 22 | June 13 | September 19 | September 3 | 115 days | 5b |
| Bozeman 6 W Experiment Farm | May 23 | June 12 | September 23 | September 4 | 123 days | 5a |
| Busby | May 23 | June 7 | September 15 | September 1 | 113 days | 4a |
| Carter (14 mi W) | May 23 | June 9 | September 23 | September 8 | 120 days | 4b |
| Chinook (35 mi SE) | May 23 | June 3 | September 23 | September 11 | 121 days | – |
| Dunkirk (19 mi NNE) | May 23 | June 8 | September 14 | September 1 | 112 days | 3b |
| Harlowton | May 23 | June 6 | September 16 | September 1 | 113 days | 4b |
| LewistownLewistown Municipal Airport | May 23 | June 8 | September 21 | September 8 | 119 days | 4b |
| Libby 1 NE Ranger Station | May 23 | June 7 | September 21 | September 3 | 120 days | 6a |
| Rudyard (19 mi S) | May 23 | June 3 | September 19 | September 5 | 119 days | – |
| Shelby | May 23 | June 6 | September 16 | September 3 | 115 days | 4a |
| Western Agricultural Research Center | May 23 | June 10 | September 21 | September 5 | 118 days | 5b |
| Chester | May 24 | June 9 | September 17 | September 3 | 115 days | 3b |
| Cut BankCut Bank Municipal Airport | May 24 | June 5 | September 15 | September 1 | 113 days | 4a |
| Darby | May 24 | June 14 | September 23 | September 4 | 118 days | 5b |
| Gildford | May 24 | June 7 | September 15 | August 29 | 114 days | 3b |
| Harlem (20 mi S) | May 24 | June 11 | September 22 | September 8 | 118 days | – |
| Laurin (2 mi NE) | May 24 | June 13 | September 22 | September 6 | 117 days | – |
| Rapelje | May 24 | June 11 | September 21 | September 4 | 116 days | 4b |
| Shonkin (7 mi S) | May 24 | June 10 | September 21 | August 31 | 119 days | – |
| Wolf Point (29 mi ENE) | May 24 | June 6 | September 14 | September 1 | 110 days | 3b |
| Cohagen | May 25 | June 9 | September 14 | August 31 | 110 days | 3b |
| Content (4 mi NNE) | May 25 | June 8 | September 14 | August 29 | 110 days | 3b |
| Plentywood | May 25 | June 8 | September 14 | September 2 | 111 days | 3b |
| Sonnette (7 mi SW) | May 25 | June 7 | September 19 | September 1 | 115 days | 4b |
| Stanford | May 25 | June 15 | September 21 | September 6 | 118 days | 4b |
| BozemanBozeman Gallatin Field | May 26 | June 12 | September 16 | September 2 | 112 days | 4a |
| Bozeman Montana State University | May 26 | June 14 | September 22 | September 5 | 116 days | 5a |
| Hysham (25 mi SSE) | May 26 | June 13 | September 16 | September 1 | 111 days | – |
| LoganLogan Landfill | May 26 | June 12 | September 15 | September 1 | 111 days | – |
| Ryegate (18 mi NNW) | May 26 | June 13 | September 18 | September 1 | 112 days | 4a |
| Simpson 6 N - Wildhorse | May 26 | June 8 | September 15 | September 1 | 110 days | 3b |
| Terry (21 mi NNW) | May 26 | June 13 | September 17 | September 1 | 113 days | – |
| Columbus | May 27 | June 12 | September 14 | September 1 | 108 days | 4b |
| Gibson (2 mi NE) | May 27 | June 12 | September 18 | September 3 | 113 days | – |
| LivingstonLivingston Mission Field | May 27 | June 14 | September 14 | August 27 | 108 days | 4b |
| Wibaux2 mi E | May 27 | June 13 | September 16 | September 2 | 112 days | 4a |
| Choteau | May 28 | June 20 | September 12 | August 30 | 104 days | 4a |
| Del Bonita | May 28 | June 12 | September 16 | August 28 | 110 days | – |
| MoccasinMoccasin Experiment Station | May 28 | June 19 | September 20 | September 4 | 112 days | 4b |
| Redstone | May 28 | June 13 | September 7 | August 22 | 101 days | – |
| Scobey4 mi NW | May 28 | June 13 | September 6 | August 24 | 99 days | 3a |
| Joliet | May 29 | June 17 | September 15 | September 1 | 107 days | 4b |
| Harlowton (11 mi NW) | May 30 | June 17 | September 20 | September 4 | 110 days | – |
| Rudyard (21 mi N) | May 30 | June 15 | September 11 | August 27 | 103 days | – |
| KalispellKalispell Glacier Airport | May 31 | June 22 | September 10 | August 26 | 100 days | 5a |
| Lewistown (11 mi SSE) | May 31 | June 18 | September 14 | August 30 | 105 days | – |
| Anaconda | June 1 | June 25 | September 14 | August 31 | 105 days | 5a |
| Denton | June 1 | June 26 | September 11 | August 29 | 101 days | 4a |
| Judith Gap | June 1 | June 16 | September 15 | August 31 | 104 days | – |
| NyeNye #2 | June 1 | June 21 | September 11 | August 25 | 100 days | 4b |
| Opheim (10 mi N) | June 1 | June 18 | September 7 | August 24 | 99 days | 3a |
| Albion (1 mi N) | June 2 | June 21 | September 6 | August 23 | 95 days | 4a |
| DillonDillon Airport | June 2 | June 21 | September 13 | August 30 | 101 days | – |
| Sun River (4 mi S) | June 2 | June 21 | September 10 | August 25 | 96 days | 3b |
| Judith Gap (13 mi E) | June 3 | June 25 | September 15 | August 29 | 100 days | – |
| Martinsdale3 mi NNW | June 3 | June 25 | September 8 | August 23 | 94 days | 4b |
| Red Lodge | June 3 | June 18 | September 19 | August 31 | 106 days | 4b |
| St. Mary1 mi SSW | June 3 | June 23 | September 8 | August 22 | 94 days | 4a |
| Adel | June 4 | June 22 | September 12 | August 26 | 98 days | – |
| Austin (1 mi W) | June 4 | June 18 | September 14 | August 30 | 100 days | – |
| Virginia City | June 4 | June 23 | September 18 | September 3 | 106 days | 5a |
| White Sulphur SpringsWhite Sulphur Springs #2 | June 4 | June 20 | September 11 | August 27 | 97 days | 4b |
| Wilsall1 mi S | June 4 | June 23 | September 6 | August 28 | 92 days | – |
| Dillon U Of Montana Western | June 5 | June 23 | September 13 | August 29 | 98 days | 5a |
| Mystic Lake | June 5 | June 21 | September 14 | August 31 | 99 days | 5a |
| Opheim (12 mi SSE) | June 5 | June 23 | September 2 | August 15 | 89 days | – |
| Alder (17 mi S) | June 6 | June 25 | September 14 | August 31 | 98 days | 5a |
| Neihart8 mi NNW | June 6 | June 28 | September 12 | August 29 | 99 days | – |
| Boulder | June 7 | June 25 | September 8 | August 25 | 90 days | 4b |
| East Glacier | June 8 | July 1 | September 5 | August 20 | 88 days | – |
| Twin Bridges | June 8 | July 1 | September 2 | August 16 | 82 days | 5a |
| Wilsall (8 mi ENE) | June 8 | June 30 | September 7 | August 21 | 89 days | 4b |
| Blackleaf | June 9 | July 2 | September 3 | August 19 | 86 days | – |
| Elliston | June 9 | June 26 | September 8 | August 26 | 91 days | – |
| Melville (4 mi W) | June 9 | June 27 | September 7 | August 21 | 88 days | 4b |
| Divide | June 10 | July 2 | September 7 | August 24 | 85 days | 4b |
| Lima | June 11 | June 30 | September 10 | August 27 | 89 days | 4b |
| Millegan (14 mi SE) | June 11 | July 3 | September 6 | August 20 | 86 days | 4a |
| Gibson Dam | June 12 | July 5 | September 8 | August 23 | 88 days | 4b |
| St Mary station | June 12 | July 3 | September 5 | August 18 | 82 days | – |
| ButteButte Bert Mooney Airport | June 13 | July 1 | September 5 | August 24 | 83 days | 4a |
| Hebgen Dam | June 15 | July 7 | September 10 | August 25 | 87 days | – |
| Lewistown (42 mi WSW) | June 15 | July 8 | September 4 | August 19 | 77 days | – |
| Ennis | June 16 | July 6 | September 4 | August 20 | 78 days | 5a |
| Tizer Gardens | June 18 | July 3 | September 5 | August 21 | 81 days | – |
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities, growing-season length); station daily lows via ACIS (zone). Growing season: NOAA's median number of days between the last spring and first autumn 32°F night. Zone: the USDA's plant hardiness rule applied to the station's own 1991-2020 coldest nights.