Frost dates / By state
Frost dates in Wyoming
NOAA 1991–2020 normals for a 32 °F freeze. Your own yard can run a little either side.
Short answer
Across 19 NOAA weather stations in Wyoming, the average last spring frost runs from May 4 at Greybull S Big Horn Airport to June 24 at Moose 1 NNE. The first fall frost comes as early as August 28 at Moose 1 NNE and as late as October 2 at Lander 11 SSE. At 2 of the 21 stations, a freeze can come in any month. Planting zones near these stations run from 4a to 5b.
Find yours by ZIP code
The table below is by weather station. For the station nearest you, and your planting zone, type your ZIP code.
Wyoming frost dates by weather station
| Station | Last spring frost | First fall frost | Frost-free | Zone nearby |
|---|---|---|---|---|
| Big Piney Marbleton Airport 6,970 ft | A freeze is possible in any month | 4a | ||
| Buffalo Johnson Co Airport 4,967 ft | May 13 1 in 10 after May 28 | October 1 1 in 10 by September 19 | 141 days | 5a |
| Casper Natrona Co Airport 5,338 ft | May 26 1 in 10 after June 10 | September 22 1 in 10 by September 5 | 119 days | 5a |
| Cheyenne 6,128 ft | May 12 1 in 10 after May 26 | October 1 1 in 10 by September 18 | 142 days | 5b |
| Douglas Converse Co Airport 4,929 ft | May 23 1 in 10 after June 7 | September 22 1 in 10 by September 9 | 122 days | – |
| Evanston Burns Fld 7,163 ft | June 3 1 in 10 after June 17 | September 25 1 in 10 by September 11 | 114 days | – |
| Gillette Campbell Airport 4,354 ft | May 22 1 in 10 after June 4 | September 25 1 in 10 by September 9 | 126 days | – |
| Greybull S Big Horn Airport 3,933 ft | May 4 1 in 10 after May 18 | October 1 1 in 10 by September 18 | 150 days | 4b |
| Lander 11 SSE 5,773 ft | May 13 1 in 10 after June 1 | October 2 1 in 10 by September 20 | 142 days | 5a |
| Lander Hunt Fld Airport 5,592 ft | May 18 1 in 10 after June 3 | September 27 1 in 10 by September 13 | 132 days | 5a |
| Laramie Rgnl Airport 7,266 ft | June 2 1 in 10 after June 18 | September 15 1 in 10 by September 3 | 105 days | – |
| Moorcroft 3S 4,325 ft | May 22 1 in 10 after June 9 | September 28 1 in 10 by September 11 | 129 days | – |
| Moose 1 NNE 6,466 ft | June 24 1 in 10 after July 11 | August 28 1 in 10 by August 8 | 65 days | 4a |
| Rawlins Muni Airport 6,736 ft | June 1 1 in 10 after June 17 | September 15 1 in 10 by September 3 | 106 days | – |
| Riverton 5,568 ft | May 16 1 in 10 after May 31 | September 28 1 in 10 by September 15 | 135 days | 5a |
| Rock Springs Airport 6,741 ft | May 22 1 in 10 after June 9 | September 28 1 in 10 by September 14 | 129 days | – |
| Sheridan Co Airport 3,945 ft | May 21 1 in 10 after June 6 | September 23 1 in 10 by September 9 | 125 days | 5a |
| Sundance 8 NNW 5,792 ft | May 23 1 in 10 after June 3 | September 24 1 in 10 by September 7 | 124 days | – |
| Torrington Muni Airport 4,205 ft | May 11 1 in 10 after May 26 | September 29 1 in 10 by September 16 | 141 days | 5a |
| Worland 4,172 ft | May 13 1 in 10 after May 27 | September 26 1 in 10 by September 14 | 136 days | – |
| Yellowstone Lake 7,835 ft | A freeze is possible in any month | – | ||
The average date is NOAA's 50% date: half of years have a later last frost, or an earlier first one. Plan by the 1-in-10 date if a freeze would cost you plants. Stations are NOAA's main weather stations, mostly airports. “Zone nearby” is the USDA 2023 zone of the nearest ZIP code within 10 miles. NOAA counts the frost season from August to July, so in the warmest places the “first fall” freeze lands after New Year.
How these dates work
Frost dates come from NOAA's 1991 to 2020 Climate Normals, which work out from each weather station's daily lows how likely the last spring freeze and the first fall freeze (32 °F) are by each date. We use the station nearest the middle of your ZIP code and show its height and distance, since a station on a hill or by a lake can differ from your yard.
The average date is the 50% date: half of years have a freeze after the spring date or before the fall one. The 1-in-10 dates are NOAA's 10% dates, the ones to plan by if a late freeze would cost you plants. Within one yard, cold air pools in low spots while walls and paving hold heat, so some corners freeze before others.
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Where the numbers come from
- USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture
- PRISM Climate Group, Oregon State University (zone data)
- NOAA NCEI, U.S. Climate Normals 1991–2020, annual/seasonal
- NOAA, Normals calculation methodology (frost-freeze probability dates)
- US Census Bureau, 2025 ZCTA gazetteer (ZIP code centers)