Blackwell climate

Blackwell Frost Dates and Growing Season

NOAA 1991-2020 normals for Blackwell 1SSW, 2.5 km from Blackwell, elevation 1033 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Blackwell 1SSW. 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 12 and the first fall freeze around October 29, a growing season of about 199 days.

Median at 36°F
last April 23, first October 20
Median at 32°F
last April 12, first October 29
Median at 28°F
last April 1, first November 6

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 6May 2Apr 29Apr 26Apr 23Apr 19Apr 16Apr 12Apr 7
32°FApr 28Apr 23Apr 19Apr 15Apr 12Apr 8Apr 4Mar 31Mar 26
28°FApr 18Apr 12Apr 8Apr 4Apr 1Mar 29Mar 26Mar 21Mar 14
24°FApr 4Mar 31Mar 28Mar 24Mar 19Mar 15Mar 11Mar 7Mar 1
20°FMar 25Mar 18Mar 13Mar 10Mar 6Mar 3Feb 28Feb 25Feb 18
16°FMar 16Mar 9Mar 4Mar 1Feb 27Feb 23Feb 18Feb 12Feb 2

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 4Oct 10Oct 15Oct 17Oct 20Oct 22Oct 25Oct 28Nov 1
32°FOct 16Oct 20Oct 23Oct 26Oct 29Nov 1Nov 3Nov 7Nov 11
28°FOct 23Oct 28Nov 1Nov 3Nov 6Nov 9Nov 13Nov 17Nov 22
24°FOct 31Nov 4Nov 8Nov 12Nov 16Nov 19Nov 23Nov 26Dec 1
20°FNov 8Nov 14Nov 19Nov 23Nov 26Nov 30Dec 2Dec 7Dec 13
16°FNov 17Nov 24Nov 29Dec 2Dec 7Dec 10Dec 16Dec 21Dec 31

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°F200193187183179176171166159
32°F220213207203199196191186178
28°F242233227222218214210205198
24°F262255249244239235229223216
20°F288279272266261256251246237
16°F315304297289284277273266258

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
4,183
Cooling degree days, base 65°F
1,793
Growing degree days, base 40°F
7,360
Growing degree days, base 45°F
5,962
Growing degree days, base 50°F
4,710
Growing degree days, base 55°F
3,597
Growing degree days, base 60°F
2,628

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January94405
February737021
March537499
April26126251
May71134530
June3355802
July0513978
August0471936
September24240666
October20547330
November536282
December865010

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 2.5 km from Blackwell. 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 USC00340818 (Blackwell 1SSW). Public domain.