Frost dates for 82602Casper, WY
The average last spring frost in Casper is May 26 and the average first fall frost is September 22, giving a typical growing season of about 117 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 26
- Average first fall frost
- Sep 22
- Growing season
- 117 days
Safer after Jun 10 (1-in-10 risk)
Possible by Sep 5 (1-in-10 risk)
Last frost typically in 211 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | May 25 · Jun 9 · Jun 25 | Aug 26 · Sep 9 · Sep 24 | 92 days | 100% |
| Frost / freeze (32°F) | May 12 · May 26 · Jun 10 | Sep 5 · Sep 22 · Oct 4 | 117 days | 100% |
| Hard freeze (28°F) | Apr 30 · May 11 · May 27 | Sep 17 · Oct 2 · Oct 15 | 141 days | 100% |
Planting calendar for Casper
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Apr 25 – Jul 1 |
| Tomatoes | Transplant outdoors | Jun 11 – Jun 2 |
| Peppers | Start seeds indoors | Apr 25 – May 26 |
| Peppers | Transplant outdoors | Jun 25 – Jul 26 |
| Eggplant | Start seeds indoors | May 12 – Jun 10 |
| Eggplant | Transplant outdoors | Jun 25 – Jul 26 |
| Cucumbers | Sow outdoors | Jun 25 – Jun 12 |
| Summer squash | Sow outdoors | Jun 11 – Jul 26 |
| Winter squash & pumpkins | Sow outdoors | Jun 25 – Jul 26 |
| Snap beans | Sow outdoors | Jun 11 – Jul 5 |
| Sweet corn | Sow outdoors | Jun 11 – Jun 2 |
| Watermelon & cantaloupe | Sow outdoors | Jun 25 – Jul 26 |
| Okra | Sow outdoors | Jun 18 – Jul 11 |
| Peas | Sow outdoors (spring) | Apr 25 – Jun 10 |
| Potatoes | Plant outdoors (spring) | Apr 25 – Jun 25 |
| Onions | Start seeds indoors (spring) | Mar 14 – Apr 10 |
| Onions | Transplant outdoors (spring) | May 12 – Jun 10 |
| Broccoli | Start seeds indoors (spring) | Apr 7 – May 11 |
| Broccoli | Transplant outdoors (spring) | May 12 – Jun 10 |
| Broccoli | Start seeds indoors (fall) | May 23 – Jun 2 |
| Broccoli | Transplant outdoors (fall) | Jun 22 – Jul 3 |
| Cabbage | Start seeds indoors (spring) | Mar 28 – Apr 25 |
| Cabbage | Transplant outdoors (spring) | Apr 25 – May 26 |
| Cabbage | Start seeds indoors (fall) | May 13 – Jun 12 |
| Cabbage | Transplant outdoors (fall) | Jun 12 – Jul 13 |
| Leaf lettuce | Sow outdoors (spring) | Apr 25 – Jul 11 |
| Leaf lettuce | Sow outdoors (fall) | Jun 12 – Jul 29 |
| Spinach | Sow outdoors (spring) | Apr 18 – Jun 1 |
| Spinach | Sow outdoors (fall) | Jun 29 – Aug 3 |
| Radishes | Sow outdoors (spring) | Apr 25 – Jun 15 |
| Radishes | Sow outdoors (fall) | Jun 12 – Aug 13 |
| Kale | Sow outdoors (spring) | May 12 – Jun 1 |
| Kale | Sow outdoors (fall) | Jun 5 – Jul 13 |
| Carrots | Sow outdoors (spring) | May 26 – Jul 11 |
| Carrots | Sow outdoors (fall) | May 13 – Jun 28 |
| Garlic | Plant outdoors (fall) | Sep 12 – Oct 13 |
Where these dates come from
ZIP code 82602 is matched to the NOAA station Casper Natrona Co Ap, WY, 8.7 km away, at 5,338 ft elevation (39 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Casper Natrona Co Ap, WY (used) | 5,338 ft | May 26 | Sep 22 |
| Casper Wwtp, WY | 5,097 ft | May 10 | Sep 29 |
| Casper 1Sw, WY | 5,143 ft | May 12 | Oct 1 |
| Bates Creek #2, WY | 6,042 ft | May 22 | Sep 26 |
Frost dates near Casper
- Casper, WY 82605 · last May 10, first Sep 29
- Mills, WY 82644 · last May 10, first Sep 29
- Evansville, WY 82636 · last May 10, first Sep 29
- Natrona, WY 82646 · last May 23, first Sep 20
- Glenrock, WY 82637 · last May 10, first Sep 29
- Alcova, WY 82620 · last May 9, first Oct 7
- Powder River, WY 82648 · last May 30, first Sep 22
- Edgerton, WY 82635 · last May 22, first Sep 22
Frequently asked questions
- When is the last frost in Casper, WY?
- For ZIP code 82602, the average last spring frost (32°F) is May 26, based on NOAA 1991-2020 climate normals for the Casper Natrona Co Ap, WY weather station. There is a 1-in-10 chance of a frost after June 10.
- When is the first frost in Casper, WY?
- The average first fall frost (32°F) is September 22. There is a 1-in-10 chance of frost by September 5, so tender plants are at risk from that point on.
- How long is the growing season in 82602?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 117 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.