Chatfield climate

Chatfield Frost Dates and Growing Season

NOAA 1991-2020 normals for Preston, 21.4 km from Chatfield, elevation 930 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Preston. 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 May 14 and the first fall freeze around September 28, a growing season of about 136 days.

Median at 36°F
last May 24, first September 19
Median at 32°F
last May 14, first September 28
Median at 28°F
last May 4, first October 5

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.

Threshold10%20%30%40%50%60%70%80%90%
36°FJun 4Jun 1May 30May 27May 24May 22May 19May 16May 10
32°FMay 27May 23May 20May 16May 14May 11May 9May 5May 1
28°FMay 18May 13May 10May 7May 4May 1Apr 29Apr 26Apr 21
24°FMay 7May 3Apr 30Apr 27Apr 23Apr 20Apr 17Apr 12Apr 8
20°FApr 29Apr 23Apr 19Apr 15Apr 11Apr 9Apr 6Apr 2Mar 30
16°FApr 19Apr 11Apr 7Apr 4Apr 2Mar 31Mar 28Mar 24Mar 18

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.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 5Sep 10Sep 14Sep 17Sep 19Sep 22Sep 25Sep 27Oct 2
32°FSep 15Sep 19Sep 22Sep 25Sep 28Sep 30Oct 2Oct 5Oct 9
28°FSep 24Sep 28Oct 1Oct 3Oct 5Oct 8Oct 11Oct 14Oct 18
24°FOct 4Oct 8Oct 11Oct 13Oct 16Oct 18Oct 21Oct 24Oct 29
20°FOct 13Oct 19Oct 21Oct 24Oct 26Oct 28Oct 31Nov 2Nov 9
16°FOct 24Oct 29Nov 1Nov 2Nov 5Nov 8Nov 12Nov 16Nov 21

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.

Threshold10%20%30%40%50%60%70%80%90%
36°F13512912412111711411010598
32°F153148144140136132128124118
28°F173167162158154151147143137
24°F195188183179175172168163157
20°F218210205200196192187183175
16°F240232226222218214210204195

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
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% 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
8,153
Cooling degree days, base 65°F
452
Growing degree days, base 40°F
4,166
Growing degree days, base 45°F
3,179
Growing degree days, base 50°F
2,307
Growing degree days, base 55°F
1,553
Growing degree days, base 60°F
927

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,58500
February1,31300
March1,062010
April640250
May31122219
June7297476
July22166609
August41118542
September19643314
October571479
November96207
December1,37800

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 21.4 km from Chatfield. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00216654 (Preston). Public domain.