Helen climate

Helen Frost Dates and Growing Season

NOAA 1991-2020 normals for Helen, 0.6 km from Helen, elevation 1493 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Helen. 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 April 11 and the first fall freeze around October 28, a growing season of about 197 days.

Median at 36°F
last April 26, first October 18
Median at 32°F
last April 11, first October 28
Median at 28°F
last March 30, first November 7

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°FMay 13May 7May 3Apr 30Apr 26Apr 23Apr 20Apr 15Apr 9
32°FMay 3Apr 25Apr 20Apr 15Apr 11Apr 8Apr 4Mar 31Mar 25
28°FApr 19Apr 9Apr 4Apr 1Mar 30Mar 25Mar 21Mar 16Mar 7
24°FMar 31Mar 25Mar 20Mar 15Mar 11Mar 6Feb 28Feb 25Feb 15
20°FMar 18Mar 11Mar 4Feb 28Feb 24Feb 18Feb 10Feb 3Jan 23
16°FMar 5Feb 27Feb 17Feb 9Feb 4Jan 31Jan 25Jan 16Jan 5

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°FOct 3Oct 8Oct 12Oct 15Oct 18Oct 21Oct 24Oct 27Nov 1
32°FOct 13Oct 18Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 10
28°FOct 22Oct 28Nov 1Nov 4Nov 7Nov 10Nov 14Nov 20Nov 27
24°FNov 2Nov 8Nov 13Nov 17Nov 21Nov 26Dec 1Dec 5Dec 12
20°FNov 16Nov 24Nov 30Dec 4Dec 8Dec 14Dec 23Dec 30Jan 8
16°FDec 3Dec 10Dec 21Dec 27Jan 1Jan 5Jan 11Jan 17Jan 30

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°F197190184179174170165160153
32°F218212206202197192186181172
28°F251240234228223218213207198
24°F284275267260255249242236225
20°F325314305297290282275268255
16°F363349339332326318308301288

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
92% 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
3,815
Cooling degree days, base 65°F
1,069
Growing degree days, base 40°F
6,694
Growing degree days, base 45°F
5,215
Growing degree days, base 50°F
3,915
Growing degree days, base 55°F
2,796
Growing degree days, base 60°F
1,849

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January808013
February645018
March509184
April25411231
May8472454
June7213655
July0321786
August1295759
September31139558
October23117270
November517168
December729020

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 0.6 km from Helen. 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 USC00094230 (Helen). Public domain.