Frost dates for 82648Powder River, WY
The average last spring frost in Powder River is May 30 and the average first fall frost is September 22, giving a typical growing season of about 115 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 30
- Average first fall frost
- Sep 22
- Growing season
- 115 days
Safer after Jun 13 (1-in-10 risk)
Possible by Sep 8 (1-in-10 risk)
Last frost typically in 215 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 26 · Jun 11 · Jun 25 | Aug 31 · Sep 13 · Sep 26 | 91 days | 100% |
| Frost / freeze (32°F) | May 12 · May 30 · Jun 13 | Sep 8 · Sep 22 · Oct 4 | 115 days | 100% |
| Hard freeze (28°F) | Apr 29 · May 12 · May 29 | Sep 16 · Oct 1 · Oct 15 | 141 days | 100% |
Planting calendar for Powder River
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 29 – Jul 5 |
| Tomatoes | Transplant outdoors | Jun 15 – Jun 2 |
| Peppers | Start seeds indoors | Apr 29 – May 30 |
| Peppers | Transplant outdoors | Jun 29 – Jul 30 |
| Eggplant | Start seeds indoors | May 16 – Jun 14 |
| Eggplant | Transplant outdoors | Jun 29 – Jul 30 |
| Cucumbers | Sow outdoors | Jun 29 – Jun 12 |
| Summer squash | Sow outdoors | Jun 15 – Jul 30 |
| Winter squash & pumpkins | Sow outdoors | Jun 29 – Jul 30 |
| Snap beans | Sow outdoors | Jun 15 – Jul 5 |
| Sweet corn | Sow outdoors | Jun 15 – Jun 2 |
| Watermelon & cantaloupe | Sow outdoors | Jun 29 – Jul 30 |
| Okra | Sow outdoors | Jun 22 – Jul 15 |
| Peas | Sow outdoors (spring) | Apr 29 – Jun 14 |
| Potatoes | Plant outdoors (spring) | Apr 29 – Jun 29 |
| Onions | Start seeds indoors (spring) | Mar 18 – Apr 14 |
| Onions | Transplant outdoors (spring) | May 16 – Jun 14 |
| Broccoli | Start seeds indoors (spring) | Apr 11 – May 15 |
| Broccoli | Transplant outdoors (spring) | May 16 – Jun 14 |
| Broccoli | Start seeds indoors (fall) | May 23 – Jun 2 |
| Broccoli | Transplant outdoors (fall) | Jun 22 – Jul 3 |
| Cabbage | Start seeds indoors (spring) | Apr 1 – Apr 29 |
| Cabbage | Transplant outdoors (spring) | Apr 29 – May 30 |
| Cabbage | Start seeds indoors (fall) | May 13 – Jun 12 |
| Cabbage | Transplant outdoors (fall) | Jun 12 – Jul 13 |
| Leaf lettuce | Sow outdoors (spring) | Apr 29 – Jul 15 |
| Leaf lettuce | Sow outdoors (fall) | Jun 12 – Jul 29 |
| Spinach | Sow outdoors (spring) | Apr 22 – Jun 5 |
| Spinach | Sow outdoors (fall) | Jun 29 – Aug 3 |
| Radishes | Sow outdoors (spring) | Apr 29 – Jun 19 |
| Radishes | Sow outdoors (fall) | Jun 12 – Aug 13 |
| Kale | Sow outdoors (spring) | May 16 – Jun 5 |
| Kale | Sow outdoors (fall) | Jun 5 – Jul 13 |
| Carrots | Sow outdoors (spring) | May 30 – Jul 15 |
| Carrots | Sow outdoors (fall) | May 13 – Jun 28 |
| Garlic | Plant outdoors (fall) | Sep 12 – Oct 13 |
Where these dates come from
ZIP code 82648 is matched to the NOAA station Powder Rvr (School), WY, 0.4 km away, at 5,722 ft elevation (7 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Powder Rvr (School), WY (used) | 5,722 ft | May 30 | Sep 22 |
| Powder River #2, WY | 5,700 ft | May 23 | Sep 20 |
| Casper Natrona Co Ap, WY | 5,338 ft | May 26 | Sep 22 |
| Casper Wwtp, WY | 5,097 ft | May 10 | Sep 29 |
Frost dates near Powder River
- Natrona, WY 82646 · last May 23, first Sep 20
- Arminto, WY 82630 · last May 30, first Sep 22
- Hiland, WY 82638 · last May 30, first Sep 22
- Casper, WY 82602 · last May 26, first Sep 22
- Mills, WY 82644 · last May 10, first Sep 29
- Alcova, WY 82620 · last May 9, first Oct 7
- Lysite, WY 82642 · last May 14, first Oct 3
- Evansville, WY 82636 · last May 10, first Sep 29
Frequently asked questions
- When is the last frost in Powder River, WY?
- For ZIP code 82648, the average last spring frost (32°F) is May 30, based on NOAA 1991-2020 climate normals for the Powder Rvr (School), WY weather station. There is a 1-in-10 chance of a frost after June 13.
- When is the first frost in Powder River, WY?
- The average first fall frost (32°F) is September 22. There is a 1-in-10 chance of frost by September 8, so tender plants are at risk from that point on.
- How long is the growing season in 82648?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 115 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.