Jefferson climate

Jefferson Frost Dates and Growing Season

NOAA 1991-2020 normals for Jefferson 2 E, 3.9 km from Jefferson, elevation 2759 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jefferson 2 E. 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 7 and the first fall freeze around October 8, a growing season of about 154 days.

Median at 36°F
last May 19, first September 30
Median at 32°F
last May 7, first October 8
Median at 28°F
last April 25, first October 18

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 3May 30May 26May 22May 19May 16May 12May 8May 3
32°FMay 24May 19May 14May 11May 7May 4May 1Apr 27Apr 22
28°FMay 13May 7May 3Apr 29Apr 25Apr 21Apr 17Apr 13Apr 8
24°FMay 1Apr 22Apr 17Apr 13Apr 11Apr 7Apr 3Mar 31Mar 26
20°FApr 13Apr 8Apr 2Mar 31Mar 28Mar 25Mar 21Mar 16Mar 9
16°FMar 31Mar 27Mar 21Mar 17Mar 12Mar 8Mar 4Feb 27Feb 16

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 14Sep 20Sep 24Sep 28Sep 30Oct 2Oct 5Oct 8Oct 12
32°FSep 25Oct 1Oct 3Oct 6Oct 8Oct 11Oct 14Oct 17Oct 22
28°FOct 6Oct 10Oct 13Oct 16Oct 18Oct 21Oct 24Oct 27Nov 1
24°FOct 13Oct 18Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 11
20°FOct 24Oct 29Nov 1Nov 4Nov 6Nov 9Nov 13Nov 18Nov 26
16°FNov 3Nov 8Nov 12Nov 16Nov 20Nov 25Nov 30Dec 4Dec 12

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°F154148142138135130126120113
32°F175168163158154150145141134
28°F197191185179175170165160152
24°F224215209204200195191186178
20°F252243236230225220215210202
16°F287274266259253248242234223

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
5,448
Cooling degree days, base 65°F
408
Growing degree days, base 40°F
4,937
Growing degree days, base 45°F
3,682
Growing degree days, base 50°F
2,608
Growing degree days, base 55°F
1,702
Growing degree days, base 60°F
964

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,00404
February83206
March733028
April460198
May22314274
June5475471
July11151604
August17122570
September10941386
October4074133
November692026
December90708

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 3.9 km from Jefferson. 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 USC00314496 (Jefferson 2 E). Public domain.