Idaho frost dates: Last spring and first autumn frost at every NOAA station, 1991-2020
Across Idaho's 127 NOAA stations with frost dates, the median last spring frost (32°F) runs from April 2 in Brownlee Dam to June 22 in McCall station; for half of its places it comes after May 15.
- Typical last spring frost
- May 15median of 76 places
- Typical first autumn frost
- September 30median of 76 places
- Earliest last frost
- April 2Brownlee Dam
- Latest last frost
- June 22McCall station
When is the last frost in Idaho, town by town?
Each date is NOAA's: "after May 15 in half of years" means the last 32°F night of spring came after May 15 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 |
|---|---|---|---|---|---|---|
| Brownlee Dam | April 2 | April 20 | November 5 | October 24 | 216 days | 8a |
| LewistonLewiston Airport | April 6 | April 26 | October 26 | October 10 | 200 days | 7b |
| Swan Falls Powerhouse | April 12 | May 6 | October 26 | October 9 | 193 days | 7b |
| Lowell Three Rivers | April 16 | May 4 | October 25 | October 5 | 191 days | 8a |
| Bruneau | April 17 | May 7 | October 17 | October 1 | 181 days | – |
| Payette | April 19 | May 5 | October 20 | October 6 | 183 days | 7a |
| Dworshak Fish Hatchery | April 20 | May 5 | October 20 | September 30 | 182 days | 7b |
| Coeur d'AleneCoeur D'alene | April 22 | May 6 | October 18 | October 4 | 179 days | 7b |
| Deer Flat Dam | April 23 | May 9 | October 18 | October 2 | 178 days | – |
| Weiser | April 23 | May 10 | October 13 | October 1 | 174 days | – |
| BoiseBoise Air Terminal | April 24 | May 9 | October 21 | October 5 | 179 days | 7b |
| Homedale1 mi SE | April 24 | May 5 | October 9 | September 26 | 169 days | – |
| Shoshone1 mi WNW | April 24 | May 12 | October 16 | October 2 | 173 days | 6b |
| BuhlBuhl #2 | April 25 | May 10 | October 15 | September 29 | 172 days | – |
| Fenn Ranger Station | April 26 | May 9 | October 20 | October 1 | 176 days | 7b |
| ParmaParma Experiment Station | April 27 | May 9 | October 9 | September 26 | 165 days | – |
| Arrowrock Dam | April 28 | May 16 | October 14 | October 1 | 169 days | – |
| Grand View4 mi NW | April 28 | May 13 | October 6 | September 24 | 162 days | – |
| Kamiah | April 29 | May 12 | October 5 | September 22 | 163 days | – |
| NampaNampa Sugar Factory | April 29 | May 18 | October 13 | September 29 | 164 days | 7a |
| Boise Lucky Peak Dam | April 30 | May 18 | October 22 | September 30 | 173 days | – |
| Bonners Ferry | April 30 | May 16 | October 4 | September 18 | 154 days | 6b |
| Emmett2 mi E | April 30 | May 17 | October 17 | October 2 | 168 days | 7a |
| Kooskia5 mi SSE | April 30 | May 13 | October 11 | September 19 | 162 days | – |
| Twin Falls-KMVT | April 30 | May 14 | October 9 | September 24 | 161 days | – |
| Glenns Ferry | May 1 | May 16 | October 3 | September 16 | 154 days | – |
| JeromeJerome County Airport | May 1 | May 16 | October 14 | September 29 | 165 days | 7a |
| Jerome station | May 2 | May 30 | October 14 | September 30 | 166 days | 6b |
| Mountain Home | May 2 | May 23 | October 8 | September 25 | 157 days | – |
| Pocatello City | May 2 | May 18 | October 11 | September 26 | 161 days | – |
| Yellowpine Bar | May 2 | May 14 | October 10 | September 26 | 159 days | 7a |
| Hagerman2 mi SW | May 3 | May 17 | October 1 | September 16 | 151 days | 6b |
| Shoup | May 3 | May 21 | October 8 | September 24 | 157 days | – |
| St. MariesSaint Maries | May 3 | May 18 | October 4 | September 18 | 152 days | 6b |
| American Falls | May 4 | May 21 | October 8 | September 22 | 155 days | – |
| Porthill (1 mi SW) | May 4 | May 28 | September 30 | September 10 | 145 days | 6b |
| BlackfootBlackfoot Fire Dept | May 5 | May 22 | October 3 | September 16 | 149 days | – |
| Wallace | May 5 | May 21 | October 2 | September 17 | 149 days | 6b |
| Cottonwood2 mi WSW | May 6 | May 26 | October 13 | September 28 | 156 days | 7a |
| Paul1 mi ENE | May 6 | May 22 | October 6 | September 22 | 151 days | 6b |
| Riggins | May 6 | May 26 | October 9 | September 24 | 155 days | – |
| Twin Falls (6 mi E) | May 6 | May 26 | October 3 | September 16 | 150 days | – |
| BurleyBurley Municipal Airport | May 7 | May 23 | October 4 | September 21 | 150 days | 6b |
| Hazelton | May 7 | May 26 | October 5 | September 19 | 149 days | 6b |
| SandpointSandpoint Experiment Station | May 8 | May 25 | September 28 | September 11 | 141 days | 6b |
| Cabinet Gorge | May 9 | May 25 | October 8 | September 25 | 153 days | 6b |
| Grangeville | May 9 | May 27 | October 3 | September 14 | 146 days | 6b |
| Idaho Falls - Kifi | May 9 | June 2 | October 1 | September 17 | 142 days | 6a |
| Rigby | May 9 | May 25 | October 5 | September 21 | 148 days | – |
| Twin FallsTwin Falls Sun Valley Regional Airport | May 9 | May 28 | October 4 | September 20 | 147 days | 6b |
| Council | May 10 | June 1 | October 2 | September 16 | 145 days | – |
| Plummer3 mi WSW | May 11 | June 4 | October 5 | September 15 | 143 days | – |
| Taylor Ranch | May 11 | June 1 | September 30 | September 15 | 140 days | 6b |
| Mullan station | May 12 | June 19 | September 30 | September 12 | 138 days | – |
| Rexburg BYU Idaho | May 12 | June 2 | September 24 | September 6 | 132 days | 5b |
| Bellevue | May 13 | June 3 | October 2 | September 15 | 139 days | – |
| American Falls (6 mi NE) | May 14 | June 4 | October 2 | September 16 | 138 days | 6a |
| ChallisChallis Airport | May 14 | June 2 | September 25 | September 10 | 131 days | 5b |
| Kellogg | May 14 | June 3 | September 26 | September 9 | 131 days | 6b |
| Cambridge | May 15 | June 4 | September 27 | September 12 | 134 days | 6a |
| Oakley | May 15 | June 6 | October 2 | September 16 | 137 days | 6b |
| Potlatch3 mi NNE | May 15 | June 2 | September 21 | August 31 | 126 days | 6b |
| RexburgRexburg Madison County Airport | May 15 | June 3 | September 23 | September 8 | 129 days | 5b |
| Elk River | May 16 | June 1 | September 23 | September 6 | 128 days | – |
| MinidokaMinidoka Dam | May 16 | June 5 | October 1 | September 13 | 136 days | 6a |
| Pocatello (2 mi NE) | May 16 | June 6 | October 2 | September 14 | 137 days | 6b |
| Preston | May 16 | June 4 | September 28 | September 14 | 133 days | 6a |
| Boise (7 mi N) | May 17 | June 10 | October 12 | September 27 | 147 days | 7a |
| Castleford2 mi N | May 17 | June 5 | September 29 | September 11 | 132 days | 6b |
| Murphy (10 mi W) | May 17 | June 6 | September 30 | September 14 | 134 days | 6b |
| SalmonSalmon-Ksra | May 17 | June 9 | September 24 | September 9 | 127 days | 5b |
| St. AnthonySaint Anthony | May 17 | June 10 | September 22 | September 5 | 126 days | 5a |
| DuboisDubois Experiment Station | May 18 | June 9 | September 30 | September 14 | 132 days | 6a |
| Lifton Pumping Station | May 19 | June 5 | September 21 | September 5 | 123 days | 5b |
| Fort Hall1 mi NNE | May 20 | June 12 | September 20 | September 1 | 119 days | 5b |
| Massacre Rocks State Park | May 20 | June 9 | September 26 | September 8 | 125 days | – |
| Priest River Experiment Station | May 20 | June 4 | September 13 | September 1 | 114 days | 6a |
| AberdeenAberdeen Experiment Station | May 21 | June 13 | September 20 | September 2 | 118 days | 5b |
| Ashton1 mi N | May 21 | June 13 | September 21 | September 4 | 121 days | 5b |
| Lava Hot Springs | May 21 | June 11 | September 21 | September 3 | 118 days | – |
| Middle Fork Lodge | May 21 | June 13 | September 18 | September 3 | 115 days | 6a |
| Reynolds | May 21 | June 12 | September 28 | September 13 | 126 days | 6b |
| Arco | May 22 | June 9 | September 22 | September 4 | 119 days | – |
| Bayview Model Basin | May 22 | June 6 | September 22 | September 3 | 122 days | 6b |
| Malad City | May 22 | June 16 | September 20 | September 4 | 116 days | – |
| Idaho FallsIdaho Falls Fanning Field | May 23 | June 13 | September 20 | September 1 | 114 days | 5b |
| McCammon | May 23 | June 10 | September 24 | September 7 | 121 days | 6a |
| PocatelloPocatello Regional Airport | May 23 | June 13 | September 18 | September 3 | 117 days | 6a |
| Winchester | May 23 | June 19 | September 25 | September 7 | 121 days | 6a |
| Arco (17 mi SW) | May 24 | June 15 | October 1 | September 16 | 130 days | 6a |
| Howe | May 24 | June 14 | September 14 | September 1 | 113 days | 5a |
| Nezperce | May 24 | June 19 | September 20 | September 1 | 116 days | 6b |
| Richfield | May 24 | June 14 | September 26 | September 10 | 123 days | 6a |
| Grace | May 29 | June 16 | September 17 | September 1 | 111 days | 5a |
| Sugar City | May 29 | June 18 | September 13 | August 30 | 106 days | – |
| Cascade1 mi NW | May 30 | June 21 | September 19 | September 3 | 110 days | 5b |
| Downey | May 31 | June 16 | September 18 | September 3 | 110 days | – |
| Ola | May 31 | June 19 | September 16 | September 2 | 108 days | 6a |
| Powell | May 31 | June 26 | September 12 | August 28 | 102 days | – |
| Prichard (3 mi ESE) | May 31 | June 23 | September 5 | August 20 | 95 days | – |
| Silver City (5 mi W) | May 31 | June 17 | October 6 | September 10 | 128 days | – |
| Garden Valley | June 1 | June 20 | September 10 | August 28 | 102 days | 6a |
| Gibbonsville #2 | June 1 | June 19 | September 17 | September 2 | 107 days | – |
| MackayMackay Lost River Ranger Station | June 1 | June 21 | September 20 | September 4 | 109 days | 5b |
| Malta (4 mi ESE) | June 1 | June 19 | September 19 | September 2 | 111 days | – |
| Hamer4 mi NW | June 3 | June 21 | September 11 | August 30 | 98 days | 4b |
| Pierce | June 3 | June 29 | September 7 | August 22 | 93 days | 6a |
| Malta | June 5 | June 23 | September 13 | August 28 | 96 days | – |
| Small (6 mi N) | June 5 | June 21 | September 20 | September 3 | 106 days | – |
| Lowman | June 6 | July 1 | September 4 | August 19 | 87 days | – |
| FairfieldFairfield Ranger Station | June 8 | June 28 | September 14 | August 29 | 97 days | – |
| Idaho Falls (16 mi SE) | June 9 | June 26 | September 11 | August 27 | 93 days | – |
| McCallMcCall Airport | June 10 | June 28 | September 10 | August 29 | 93 days | 5b |
| MullanMullan Pass Vor/Dme | June 10 | June 25 | September 23 | September 4 | 104 days | 6a |
| Idaho Falls (46 mi W) | June 11 | July 1 | September 6 | August 24 | 89 days | 4b |
| May (2 mi SSE) | June 12 | June 29 | September 6 | August 23 | 85 days | – |
| Monteview | June 12 | June 30 | September 7 | August 25 | 87 days | – |
| Yellowpine | June 12 | July 5 | September 11 | August 26 | 88 days | – |
| Driggs | June 13 | June 28 | September 9 | August 26 | 86 days | 5a |
| Chilly Barton Flat | June 14 | June 30 | September 8 | August 26 | 86 days | 5a |
| TetoniaTetonia Experiment Station | June 15 | June 29 | September 7 | August 24 | 85 days | – |
| Hill City (1 mi W) | June 16 | July 3 | September 6 | August 20 | 80 days | – |
| Picabo | June 16 | June 30 | September 9 | August 25 | 85 days | 5b |
| Bern | June 17 | July 4 | September 3 | August 18 | 77 days | 5a |
| Idaho City | June 17 | July 4 | September 5 | August 23 | 80 days | – |
| Craters Of The Moon | June 19 | July 2 | September 9 | August 25 | 81 days | 5b |
| McCall station | June 22 | July 10 | September 2 | August 14 | 72 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.