Frost dates for Conowingo Dam, MD
At Conowingo Dam, the median last spring frost (32°F) is Apr 3 and the median first fall frost is Nov 6, for a typical growing season of 217 days. For a 90% chance that the last frost has passed, wait until Apr 18. Nearby ZIP codes are in USDA hardiness zones 7a to 7b.
- Apr 3Last spring frost (median)50% chance of 32°F after this date
- Apr 18Safer planting date10% chance of 32°F after this date
- Nov 6First fall frost (median)50% chance of 32°F by this date
- 217 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Apr 3 | Apr 18 | May 5 |
| 32°F | Mar 22 | Apr 3 | Apr 18 |
| 28°F | Mar 8 | Mar 24 | Apr 6 |
| 24°F | Feb 27 | Mar 13 | Mar 28 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Oct 13 | Oct 28 | Nov 7 |
| 32°F | Oct 26 | Nov 6 | Nov 19 |
| 28°F | Nov 4 | Nov 17 | Dec 1 |
| 24°F | Nov 12 | Nov 29 | Dec 23 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 172 days | 193 days | 213 days |
| 32°F | 197 days | 217 days | 236 days |
| 28°F | 219 days | 238 days | 261 days |
| 24°F | 238 days | 262 days | 286 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 21918 | 7a | 0 to 5°F | 3 km |
| 21034 | 7a | 0 to 5°F | 4 km |
| 21917 | 7a | 0 to 5°F | 7 km |
| 21904 | 7a | 0 to 5°F | 10 km |
| 17563 | 7a | 0 to 5°F | 12 km |
| 21028 | 7a | 0 to 5°F | 12 km |
| 21160 | 7a | 0 to 5°F | 12 km |
| 21903 | 7b | 5 to 10°F | 14 km |
| 21154 | 7a | 0 to 5°F | 16 km |
| 17314 | 7a | 0 to 5°F | 17 km |
| 21914 | 7b | 5 to 10°F | 19 km |
| 21901 | 7b | 5 to 10°F | 20 km |
| 21050 | 7b | 5 to 10°F | 20 km |
| 21132 | 7a | 0 to 5°F | 22 km |
| 21084 | 7a | 0 to 5°F | 25 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00182060, at 39.6556, -76.1750, elevation 12 m (40 ft).
- Data quality: Representative (10+ years), 21 years of freeze data.
- Average days per year at or below 32°F: 106.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Aberdeen Phillips Field (20 km)
- Chestertown (50 km)
- Cylburn (53 km)
- Millers 4 NE (54 km)
- Md Sci Center Baltimore (56 km)
- Baltimore Wash Intl Airport (70 km)
- Stevensville 2sw (77 km)
- Annapolis Naf (79 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.