Seeley Frost Dates and Growing Season

NOAA 1991-2020 normals for El Centro Naf, 2.7 km from Seeley, elevation -42 ft

Frost and the growing season

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

The last spring freeze typically comes around January 6 and the first fall freeze around December 21, a growing season of about 347 days.

Median at 36°F: last February 1, first December 8
Median at 32°F: last January 6, first December 21
Median at 28°F: last January 3, first December 31

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 25	Feb 18	Feb 12	Feb 6	Feb 1	Jan 26	Jan 18	Jan 12	Jan 5
32°F	Feb 6	Jan 30	Jan 19	Jan 11	Jan 6	Jan 1	Dec 28	Dec 21	Dec 14
28°F	Jan 31	Jan 24	Jan 12	Jan 6	Jan 3	Dec 31	Dec 26	Dec 19	Dec 12
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	Nov 23	Nov 28	Dec 1	Dec 5	Dec 8	Dec 11	Dec 15	Dec 19	Dec 25
32°F	Dec 5	Dec 9	Dec 13	Dec 16	Dec 21	Dec 25	Dec 29	Jan 2	Jan 12
28°F	Dec 10	Dec 16	Dec 22	Dec 28	Dec 31	Jan 4	Jan 6	Jan 18	Jan 29
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	341	331	323	316	309	302	296	289	280
32°F	365	365	360	353	347	342	334	326	316
28°F	365	365	365	365	365	365	365	360	348
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: 100% of years
32°F or colder: 79% of years
28°F or colder: 25% of years
24°F or colder: 3% 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: 931
Cooling degree days, base 65°F: 4,103
Growing degree days, base 40°F: 12,298
Growing degree days, base 45°F: 10,476
Growing degree days, base 50°F: 8,674
Growing degree days, base 55°F: 6,959
Growing degree days, base 60°F: 5,424

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	272	1	205
February	154	14	282
March	63	90	493
April	13	207	644
May	1	412	876
June	0	640	1,090
July	0	843	1,308
August	0	856	1,321
September	0	655	1,105
October	6	325	784
November	102	58	408
December	320	1	158

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 2.7 km from Seeley. 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 USW00023199 (El Centro Naf). Public domain.