Frost Dates
Frost Dates · California

Frost dates for Modesto, California

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

Typical last spring freeze (32°F)
January 31
median date, 1991–2020
Typical first fall freeze (32°F)
December 5
median date, 1991–2020
Typical frost-free season
308 days
between the median dates

In a typical year, the last spring freeze around Modesto comes near January 31 and the first fall freeze near December 5. One year in ten, a freeze still arrives after February 25 in spring — and one year in ten, the first fall freeze has already landed by November 20. NCEI's own growing-season statistic (days between freezes, percentiled per year) puts the median at 312 days.

JFMAMJJASONDJanuary 31December 5
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 Modesto City Co Ap, CA (USW00023258), 3.0 mi from the city's census reference point, elev. 73 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)February 3March 1March 31November 8November 22December 9
32°F — freezingDecember 31January 31February 25November 20December 5January 6
28°F — hard freezeDecember 16January 8February 6December 1December 21January 20

Measured at Modesto City Co Ap, CA (USW00023258), 3.0 mi from the city's census reference point, elev. 73 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)February 25November 20268 days
Typical (median freeze dates)January 31December 5308 days
Gambler's (9-in-10 freeze risk at each end)December 31January 6365 days (effectively year-round at this risk level)

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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