Princeton Frost Dates and Growing Season

NOAA 1991-2020 normals for Perrine 4W, 5.6 km from Princeton, elevation 10 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Perrine 4W. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

A freeze (32°F or colder) happens in only 11 percent of years at Perrine 4W, so there is no typical freeze season.

Median at 36°F: last January 25, first January 15
Median at 32°F: last January 18, first January 13

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Feb 23	Feb 11	Feb 3	Jan 30	Jan 25	Jan 18	Jan 12	Jan 6	Dec 30
32°F	Feb 1	Jan 31	Jan 29	Jan 26	Jan 18	Jan 12	Jan 7	Jan 4	Dec 31
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Dec 20	Dec 30	Jan 4	Jan 9	Jan 15	Jan 22	Jan 28	Feb 2	Feb 13
32°F	Dec 31	Jan 3	Jan 5	Jan 9	Jan 13	Jan 24	Jan 27	Jan 30	Feb 1
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	365	365	365	365	365	358	346	334	318
32°F	365	365	365	365	365	365	365	365	361
28°F	365	365	365	365	365	365	365	365	365
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder: 50% of years
32°F or colder: 11% of years
28°F or colder: 1% of years
24°F or colder: 0% of years
20°F or colder: 0% of years
16°F or colder: 0% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F: 214
Cooling degree days, base 65°F: 3,721
Growing degree days, base 40°F: 12,632
Growing degree days, base 45°F: 10,807
Growing degree days, base 50°F: 8,986
Growing degree days, base 55°F: 7,179
Growing degree days, base 60°F: 5,408

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	78	94	484
February	48	113	486
March	25	171	611
April	4	257	704
May	0	371	836
June	0	460	911
July	0	504	969
August	0	519	984
September	0	473	923
October	1	389	853
November	10	225	665
December	48	146	564

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 5.6 km from Princeton. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00087020 (Perrine 4W). Public domain.