Frost Dates
Frost Dates · Colorado

Frost dates for Centennial, Colorado

Colorado · first & last freeze, from NOAA 1991–2020 climate normals

Typical last spring freeze (32°F)
May 5
median date, 1991–2020
Typical first fall freeze (32°F)
October 8
median date, 1991–2020
Typical frost-free season
156 days
between the median dates

In a typical year, the last spring freeze around Centennial comes near May 5 and the first fall freeze near October 8. One year in ten, a freeze still arrives after May 17 in spring — and one year in ten, the first fall freeze has already landed by September 25. NCEI's own growing-season statistic (days between freezes, percentiled per year) puts the median at 154 days.

JFMAMJJASONDMay 5October 8
The year at a glance: blue bands span the 9-in-10 to 1-in-10 range where the last spring / first fall 32°F freeze lands; the green band is the typical frost-free window between the median dates. Measured at Denver Centennial Ap, CO (USW00093067), 1.6 mi from the city's census reference point, elev. 5,883 ft. NOAA/NCEI 1991–2020 normals.

Freeze-date probabilities, three thresholds

ThresholdLast spring — 9 in 10 years past byLast spring — typical (median)Last spring — 1 in 10 years later thanFirst fall — 1 in 10 years byFirst fall — typical (median)First fall — 9 in 10 years by
36°F — near-freezing (frost can occur)May 3May 15May 30September 17October 1October 12
32°F — freezingApril 24May 5May 17September 25October 8October 20
28°F — hard freezeApril 10April 25May 9October 4October 17October 28

Measured at Denver Centennial Ap, CO (USW00093067), 1.6 mi from the city's census reference point, elev. 5,883 ft. NOAA/NCEI 1991–2020 normals. Read each date column as odds over the 30-year record — e.g. "9 in 10 years past by" means only one spring in ten saw a later freeze than that date.

Frost-free windows (computed)

Window (32°F ends)OpensClosesLength
Cautious (1-in-10 freeze risk at each end)May 17September 25131 days
Typical (median freeze dates)May 5October 8156 days
Gambler's (9-in-10 freeze risk at each end)April 24October 20179 days

Pure arithmetic on the freeze-date percentiles above — the "cautious" window opens on the date only 1 year in 10 still sees a later spring freeze, and closes on the date by which only 1 year in 10 has already frozen.

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