Frost dates for Conowingo Dam, Maryland
Half of years have their last spring frost by April 3 — but 1 year in 10 still frosts after April 18.
Every other site gives you one date. A frost date is not a date: it is a percentile from 30 years of records at a nearby weather station, and planting to the median means losing the crop in half of years. Both numbers are below, so you can choose the risk yourself.
The odds
- Frost this late in 1 year in 10
- April 18
- 1 year in 5
- April 14
- 3 years in 10
- April 9
- 2 years in 5
- April 6
- Half of years (the median)
- April 3
- First fall freeze, typical year
- November 6
- Growing season
- about 217 days
- Hardiness zones nearby
- 7a, 7b
Where these numbers come from
NOAA NCEI 1991–2020 Climate Normals, station Conowingo Dam (USC00182060), at 39.66, -76.17. These are that station's own records, unshifted. The further your garden is from it, the less exactly they describe your ground — the planner resolves the nearest station to your own ZIP and lowers its confidence with distance, rather than presenting one number as if it were measured in your yard.
Cold air also pools in low ground on the clear, still nights when frost happens, so a hollow can freeze while a slope a hundred metres away does not. No table can know that about your garden. Your own logged frosts eventually can.
ZIP codes nearest this station
17302, 17314, 17321, 17509, 17518, 17532, 17536, 17563, 17566, 19362, 19363, 21001, 21005, 21009, 21013, 21014, 21015, 21017, 21028, 21034, 21040, 21047, 21050, 21051, 21078, 21082, 21084, 21085, 21087, 21130, 21132, 21154, 21156, 21160, 21901, 21902, 21903, 21904, 21911, 21914, 21917, 21918.