Harlem climate

Harlem Frost Dates and Growing Season

NOAA 1991-2020 normals for Harlem, 0.9 km from Harlem, elevation 2371 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Harlem. 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 16 and the first fall freeze around September 21, a growing season of about 125 days.

Median at 36°F
last May 29, first September 9
Median at 32°F
last May 16, first September 21
Median at 28°F
last May 6, first September 29

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 13Jun 7Jun 3May 31May 29May 26May 23May 19May 16
32°FMay 31May 26May 22May 19May 16May 14May 11May 9May 4
28°FMay 20May 14May 11May 9May 6May 3May 1Apr 29Apr 24
24°FMay 9May 5May 2Apr 30Apr 27Apr 24Apr 20Apr 16Apr 10
20°FMay 2Apr 26Apr 22Apr 19Apr 15Apr 12Apr 7Apr 4Mar 30
16°FApr 20Apr 15Apr 11Apr 7Apr 3Mar 31Mar 27Mar 21Mar 14

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°FAug 26Sep 1Sep 4Sep 7Sep 9Sep 12Sep 15Sep 19Sep 23
32°FSep 8Sep 12Sep 15Sep 18Sep 21Sep 23Sep 25Sep 28Oct 2
28°FSep 17Sep 21Sep 24Sep 27Sep 29Oct 1Oct 4Oct 7Oct 12
24°FSep 23Sep 28Oct 1Oct 5Oct 8Oct 11Oct 14Oct 17Oct 21
20°FSep 30Oct 5Oct 10Oct 14Oct 17Oct 20Oct 23Oct 26Oct 30
16°FOct 9Oct 17Oct 21Oct 24Oct 27Oct 29Nov 1Nov 5Nov 11

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°F12111511110710399959082
32°F143136132129125121118113108
28°F163157152149145142137133127
24°F183176171167163159155149144
20°F206198192188183177172166159
16°F229222215210206200196190180

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
8,168
Cooling degree days, base 65°F
380
Growing degree days, base 40°F
3,938
Growing degree days, base 45°F
2,933
Growing degree days, base 50°F
2,071
Growing degree days, base 55°F
1,350
Growing degree days, base 60°F
784

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50000
February1,23800
March1,00906
April620036
May3398181
June11746381
July29161597
August45142564
September23522256
October619048
November1,01703
December1,40100

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 0.9 km from Harlem. 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 USC00243929 (Harlem). Public domain.