Wyoming frost dates: Last spring and first autumn frost at every NOAA station, 1991-2020
Across Wyoming's 129 NOAA stations with frost dates, the median last spring frost (32°F) runs from April 28 in Basin to June 24 in Moose (1 mi NNE); for half of its places it comes after May 20.
- Typical last spring frost
- May 20median of 58 places
- Typical first autumn frost
- September 24median of 58 places
- Earliest last frost
- April 28Basin
- Latest last frost
- June 24Moose (1 mi NNE)
When is the last frost in Wyoming, town by town?
Each date is NOAA's: "after May 20 in half of years" means the last 32°F night of spring came after May 20 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 |
|---|---|---|---|---|---|---|
| Basin | April 28 | May 11 | October 10 | September 26 | 164 days | 4b |
| GreybullGreybull S Big Horn Airport | May 4 | May 18 | October 1 | September 18 | 149 days | 4b |
| Worland station | May 4 | May 18 | October 1 | September 21 | 149 days | – |
| Boysen Dam | May 5 | May 20 | October 7 | September 24 | 153 days | 5a |
| Thermopolis | May 5 | May 19 | October 5 | September 23 | 152 days | 5a |
| Deaver | May 6 | May 20 | October 1 | September 19 | 148 days | 5a |
| Colony | May 7 | May 21 | October 3 | September 19 | 149 days | – |
| Guernsey2 mi NW | May 7 | May 21 | October 6 | September 23 | 152 days | 5a |
| Shoshoni | May 7 | May 18 | October 3 | September 23 | 145 days | – |
| Whalen Dam USBR | May 7 | May 24 | October 3 | September 21 | 146 days | – |
| GlendoGlendo Reservoir USBR | May 9 | May 24 | October 5 | September 21 | 148 days | 4a |
| Lovell | May 9 | May 25 | September 29 | September 16 | 142 days | 5a |
| Pathfinder Dam | May 9 | May 23 | October 7 | September 22 | 148 days | – |
| Casper Wastewater Treatment Plant | May 10 | May 24 | September 29 | September 14 | 138 days | 5a |
| Pine Bluffs1 mi ESE | May 10 | May 24 | October 1 | September 17 | 142 days | – |
| Tensleep (4 mi NE) | May 10 | May 26 | October 1 | September 18 | 141 days | – |
| Greybull station | May 11 | May 24 | September 23 | September 11 | 133 days | 4b |
| Guernsey Dam #2 | May 11 | May 25 | October 3 | September 19 | 144 days | – |
| TorringtonTorrington Municipal Airport | May 11 | May 26 | September 29 | September 16 | 139 days | 5a |
| Casper (1 mi SW) | May 12 | May 26 | October 1 | September 18 | 143 days | – |
| CheyenneCheyenne Weather Office Airport | May 12 | May 26 | October 1 | September 18 | 141 days | 5b |
| Cody | May 12 | May 27 | October 1 | September 17 | 140 days | 5a |
| Emblem | May 12 | May 27 | September 28 | September 14 | 136 days | 5a |
| Riverton station | May 12 | May 26 | September 24 | September 11 | 132 days | – |
| Seminoe Reservoir USBR | May 12 | May 25 | October 4 | September 23 | 143 days | – |
| BuffaloBuffalo Johnson County Airport | May 13 | May 28 | October 1 | September 19 | 141 days | 5b |
| Lander (11 mi SSE) | May 13 | June 1 | October 2 | September 20 | 140 days | – |
| Newcastle | May 13 | May 26 | October 3 | September 17 | 143 days | 5a |
| Worland | May 13 | May 27 | September 26 | September 14 | 133 days | 4b |
| Albin | May 14 | May 25 | October 2 | September 18 | 142 days | 5b |
| Black Mountain | May 14 | June 1 | October 3 | September 20 | 140 days | 5b |
| Carpenter3 mi N | May 14 | May 27 | September 26 | September 12 | 133 days | – |
| Cheyenne Weather Office | May 14 | May 28 | October 1 | September 17 | 139 days | – |
| La Grange | May 14 | May 29 | October 1 | September 15 | 137 days | 5a |
| Leiter (9 mi N) | May 14 | May 29 | September 30 | September 17 | 137 days | 5a |
| Lusk (25 mi NE) | May 14 | May 27 | October 1 | September 19 | 139 days | – |
| Old Fort Laramie | May 14 | May 27 | September 26 | September 12 | 134 days | 4b |
| Pavillion | May 14 | May 29 | September 30 | September 18 | 139 days | – |
| Torrington Experiment Farm | May 14 | May 28 | September 24 | September 10 | 130 days | – |
| Dull Center (1 mi SE) | May 15 | May 28 | September 27 | September 13 | 133 days | 4b |
| Gillette (4 mi SE) | May 15 | May 27 | October 1 | September 15 | 136 days | 5a |
| Heart Mountain | May 15 | June 1 | September 25 | September 11 | 132 days | 5a |
| Yoder5 mi W | May 15 | June 2 | September 27 | September 12 | 132 days | – |
| Pine Bluffs (5 mi W) | May 16 | June 1 | September 27 | September 13 | 132 days | 5a |
| Redbird | May 16 | May 31 | September 24 | September 10 | 130 days | 4a |
| Riverton | May 16 | May 31 | September 28 | September 15 | 133 days | 5a |
| Shell | May 16 | June 3 | September 24 | September 10 | 130 days | 4b |
| Big Horn | May 17 | May 31 | September 28 | September 13 | 132 days | – |
| Buffalo Bill Dam | May 17 | June 3 | October 3 | September 18 | 136 days | – |
| Hulett | May 17 | May 30 | September 23 | September 8 | 128 days | – |
| Lance Creek (11 mi NNE) | May 17 | June 3 | September 25 | September 9 | 129 days | 4b |
| Rawlins (1 mi N) | May 17 | May 31 | October 2 | September 22 | 138 days | – |
| Torrington (29 mi N) | May 17 | May 31 | September 28 | September 15 | 133 days | 5a |
| Chugwater | May 18 | June 2 | September 24 | September 9 | 129 days | 5a |
| Clark (3 mi NE) | May 18 | June 4 | September 22 | September 8 | 125 days | 4b |
| Kaycee | May 18 | May 31 | September 25 | September 11 | 129 days | 4b |
| LanderLander Airport | May 18 | June 3 | September 27 | September 13 | 131 days | 5a |
| Sheridan Field Station | May 18 | June 2 | September 24 | September 9 | 127 days | 4b |
| Billy Creek | May 19 | May 31 | September 21 | September 6 | 123 days | 4b |
| Douglas (1 mi SE) | May 19 | June 2 | September 23 | September 10 | 126 days | 4b |
| PowellPowell Field Station | May 19 | June 4 | September 20 | September 7 | 123 days | 5a |
| Wheatland4 mi N | May 19 | June 2 | September 22 | September 8 | 125 days | 5a |
| Leo (6 mi SW) | May 20 | June 13 | September 28 | September 9 | 128 days | – |
| Lingle2 mi WSW | May 20 | June 7 | September 22 | September 8 | 122 days | – |
| Upton | May 20 | June 4 | September 23 | September 7 | 123 days | 4b |
| Archer | May 21 | June 6 | September 24 | September 8 | 124 days | – |
| Diversion Dam | May 21 | June 6 | September 20 | September 5 | 119 days | – |
| Echeta (2 mi NW) | May 21 | June 3 | September 23 | September 8 | 123 days | – |
| Muddy Gap | May 21 | June 10 | September 27 | September 12 | 126 days | – |
| Phillips | May 21 | June 7 | September 21 | September 8 | 121 days | 5a |
| SheridanSheridan Airport | May 21 | June 6 | September 23 | September 9 | 123 days | 5a |
| Sundance station | May 21 | June 5 | September 25 | September 7 | 124 days | – |
| Bates Creek #2 | May 22 | June 6 | September 26 | September 11 | 125 days | 5b |
| GilletteGillette Campbell Airport | May 22 | June 4 | September 25 | September 9 | 125 days | 5a |
| Laramie (4 mi SE) | May 22 | June 4 | September 28 | September 16 | 126 days | 5a |
| Midwest | May 22 | June 6 | September 22 | September 8 | 121 days | 5a |
| Moorcroft3 mi S | May 22 | June 9 | September 28 | September 11 | 127 days | – |
| Rock SpringsRock Springs Airport | May 22 | June 9 | September 28 | September 14 | 126 days | 5b |
| Sybille Research Unit | May 22 | June 5 | September 24 | September 9 | 125 days | 5b |
| Tensleep (16 mi SSE) | May 22 | June 7 | September 18 | September 4 | 117 days | 3b |
| Devils Tower #2 | May 23 | June 6 | September 20 | September 4 | 118 days | – |
| DouglasDouglas Converse County Airport | May 23 | June 7 | September 22 | September 9 | 122 days | 4b |
| Lusk2 mi SW | May 23 | June 8 | September 20 | September 4 | 119 days | – |
| Powder RiverPowder River #2 | May 23 | June 5 | September 20 | September 7 | 121 days | – |
| Sundance8 mi NNW | May 23 | June 3 | September 24 | September 7 | 121 days | – |
| Weston (1 mi E) | May 23 | June 5 | September 18 | September 1 | 118 days | – |
| Buckboard Marina | May 24 | June 8 | September 23 | September 8 | 118 days | 5a |
| Buffalo station | May 24 | June 9 | September 21 | September 7 | 118 days | 5a |
| Clearmont5 mi SW | May 24 | June 8 | September 16 | September 3 | 114 days | 4b |
| Cody (12 mi SE) | May 24 | June 11 | September 15 | September 1 | 114 days | – |
| Dayton | May 24 | June 7 | September 18 | September 2 | 114 days | – |
| Green River | May 24 | June 10 | September 22 | September 7 | 120 days | – |
| Rock Springs Fire Dept | May 24 | June 9 | September 24 | September 9 | 121 days | – |
| Story | May 24 | June 9 | September 23 | September 8 | 120 days | 5a |
| Thermopolis (9 mi NE) | May 24 | June 9 | September 16 | September 4 | 112 days | – |
| Church Buttes Gas Plant | May 25 | June 11 | September 27 | September 14 | 124 days | – |
| Dillinger | May 25 | June 8 | September 17 | September 3 | 113 days | 4b |
| Glendo (6 mi NE) | May 25 | June 11 | September 15 | September 4 | 112 days | – |
| Rochelle (7 mi ENE) | May 25 | June 11 | September 14 | August 31 | 110 days | – |
| Wright (12 mi W) | May 25 | June 8 | September 23 | September 8 | 120 days | 4b |
| CasperCasper-Natrona County Airport | May 26 | June 10 | September 22 | September 5 | 117 days | 4b |
| Hecla (1 mi E) | May 27 | June 13 | September 19 | September 3 | 115 days | 5a |
| Wapiti (1 mi WSW) | May 27 | June 12 | September 25 | September 7 | 121 days | – |
| Elk Mountain | May 28 | June 13 | September 13 | August 30 | 108 days | – |
| Cody (21 mi SW) | May 29 | June 17 | September 18 | September 3 | 110 days | – |
| Thermopolis (21 mi WNW) | May 29 | June 19 | September 17 | September 3 | 110 days | – |
| Powder River (School) | May 30 | June 13 | September 22 | September 8 | 115 days | – |
| Baggs | June 1 | June 18 | September 18 | September 4 | 108 days | 4b |
| Bitter Creek (4 mi NE) | June 1 | June 21 | September 16 | September 2 | 106 days | 4a |
| Burris | June 1 | June 19 | September 14 | September 1 | 104 days | 4b |
| Jeffrey City | June 1 | June 16 | September 13 | September 1 | 104 days | 4a |
| Medicine Bow | June 1 | June 19 | September 8 | August 28 | 97 days | – |
| RawlinsRawlins Municipal Airport | June 1 | June 17 | September 15 | September 3 | 105 days | 5a |
| Centennial1 mi NE | June 2 | June 20 | September 19 | September 3 | 106 days | – |
| Double Four Ranch | June 2 | June 25 | September 9 | August 26 | 99 days | 4b |
| LaramieLaramie Regional Airport | June 2 | June 18 | September 15 | September 3 | 102 days | 4b |
| Saratoga | June 2 | June 21 | September 12 | August 12 | 101 days | – |
| EvanstonEvanston Burns Field | June 3 | June 17 | September 25 | September 11 | 113 days | 6a |
| Yellowstone Park Mammoth | June 3 | June 19 | September 14 | August 31 | 102 days | 5a |
| Wamsutter | June 5 | June 23 | September 14 | September 1 | 101 days | 4b |
| Laramie (2 mi NW) | June 7 | June 29 | September 4 | August 17 | 88 days | – |
| La Barge | June 9 | June 27 | September 4 | August 21 | 84 days | – |
| Evanston (1 mi E) | June 12 | July 2 | September 12 | August 26 | 90 days | 5b |
| Saratoga (4 mi N) | June 12 | June 30 | September 7 | August 22 | 83 days | – |
| Alta1 mi NNW | June 14 | July 4 | September 11 | August 28 | 85 days | 5b |
| Mountain View | June 14 | July 1 | September 9 | August 23 | 84 days | 5b |
| Afton | June 20 | July 7 | September 1 | August 12 | 71 days | – |
| Moose | June 20 | July 9 | August 31 | August 12 | 70 days | – |
| Moose (1 mi NNE) | June 24 | July 11 | August 28 | August 8 | 63 days | 4a |
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.