Graham County climate

Graham County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hill City 1E, 4.9 km from Graham County, elevation 2132 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hill City 1E. 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 29 and the first fall freeze around October 13, a growing season of about 166 days.

Median at 36°F
last May 6, first October 3
Median at 32°F
last April 29, first October 13
Median at 28°F
last April 19, first October 22

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 21May 15May 11May 9May 6May 4May 2Apr 30Apr 25
32°FMay 11May 6May 3May 1Apr 29Apr 26Apr 22Apr 19Apr 14
28°FMay 1Apr 28Apr 25Apr 21Apr 19Apr 15Apr 12Apr 9Apr 4
24°FApr 23Apr 18Apr 14Apr 11Apr 7Apr 5Apr 2Mar 30Mar 22
20°FApr 14Apr 9Apr 4Apr 2Mar 31Mar 26Mar 22Mar 16Mar 9
16°FApr 6Mar 31Mar 27Mar 23Mar 18Mar 13Mar 9Mar 5Feb 28

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 21Sep 26Sep 28Oct 1Oct 3Oct 6Oct 9Oct 12Oct 16
32°FSep 29Oct 3Oct 7Oct 10Oct 13Oct 16Oct 19Oct 21Oct 25
28°FOct 8Oct 13Oct 17Oct 19Oct 22Oct 24Oct 27Oct 30Nov 3
24°FOct 18Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 8Nov 12
20°FOct 24Oct 30Nov 1Nov 4Nov 7Nov 9Nov 13Nov 17Nov 23
16°FOct 30Nov 4Nov 7Nov 11Nov 15Nov 19Nov 23Nov 28Dec 3

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°F164160156153150146142138130
32°F185178174170166163158154147
28°F206199194189185181177172166
24°F228220214209205201197192184
20°F245238233228223218213209201
16°F266258251246241236230224215

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
5,739
Cooling degree days, base 65°F
1,196
Growing degree days, base 40°F
5,833
Growing degree days, base 45°F
4,629
Growing degree days, base 50°F
3,570
Growing degree days, base 55°F
2,647
Growing degree days, base 60°F
1,858

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12501
February93905
March734038
April4395124
May18261359
June20242672
July2404866
August6331790
September84137507
October38316181
November744026
December1,08001

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 4.9 km from Graham County. 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 USC00143665 (Hill City 1E). Public domain.