Jefferson climate

Jefferson Frost Dates and Growing Season

NOAA 1991-2020 normals for Jefferson, 2.1 km from Jefferson, elevation 1235 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jefferson. 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 8 and the first fall freeze around October 1, a growing season of about 146 days.

Median at 36°F
last May 22, first September 19
Median at 32°F
last May 8, first October 1
Median at 28°F
last April 27, first October 16

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 5Jun 1May 29May 26May 22May 19May 16May 12May 7
32°FMay 23May 18May 14May 11May 8May 5May 3Apr 30Apr 27
28°FMay 10May 4May 1Apr 29Apr 27Apr 25Apr 23Apr 19Apr 14
24°FApr 27Apr 23Apr 21Apr 18Apr 15Apr 12Apr 9Apr 7Apr 4
20°FApr 19Apr 15Apr 11Apr 9Apr 7Apr 5Apr 3Apr 1Mar 29
16°FApr 11Apr 8Apr 5Apr 4Apr 2Apr 1Mar 30Mar 25Mar 20

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 6Sep 10Sep 13Sep 17Sep 19Sep 23Sep 25Sep 29Oct 4
32°FSep 16Sep 22Sep 25Sep 29Oct 1Oct 5Oct 7Oct 11Oct 17
28°FSep 29Oct 4Oct 8Oct 12Oct 16Oct 19Oct 23Oct 28Nov 1
24°FOct 17Oct 22Oct 26Oct 29Nov 1Nov 3Nov 5Nov 10Nov 15
20°FOct 31Nov 2Nov 5Nov 8Nov 12Nov 14Nov 17Nov 20Nov 25
16°FNov 7Nov 12Nov 15Nov 18Nov 21Nov 23Nov 26Nov 29Dec 2

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°F140132127123120116111107101
32°F165158153149146142138133126
28°F192186181176172168163157150
24°F217211207203199195191186178
20°F234229225222218215211207202
16°F249243238235231228224221215

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
8,391
Cooling degree days, base 65°F
219
Growing degree days, base 40°F
3,552
Growing degree days, base 45°F
2,609
Growing degree days, base 50°F
1,797
Growing degree days, base 55°F
1,110
Growing degree days, base 60°F
574

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,49400
February1,28900
March1,15805
April733125
May3777156
June14238351
July4194517
August6960457
September27618223
October590154
November93008
December1,29300

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 2.1 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 USC00274329 (Jefferson). Public domain.