Jefferson climate

Jefferson Frost Dates and Growing Season

NOAA 1991-2020 normals for Jefferson Wwtp, 1.3 km from Jefferson, elevation 783 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jefferson Wwtp. 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 25 and the first fall freeze around October 18, a growing season of about 173 days.

Median at 36°F
last May 6, first October 5
Median at 32°F
last April 25, first October 18
Median at 28°F
last April 15, first October 29

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 20May 15May 12May 9May 6May 3May 1Apr 27Apr 23
32°FMay 9May 4May 1Apr 28Apr 25Apr 22Apr 19Apr 16Apr 12
28°FApr 29Apr 24Apr 20Apr 18Apr 15Apr 11Apr 9Apr 6Apr 2
24°FApr 19Apr 14Apr 10Apr 7Apr 4Apr 2Mar 31Mar 27Mar 22
20°FApr 9Apr 4Apr 1Mar 30Mar 27Mar 24Mar 21Mar 17Mar 12
16°FMar 31Mar 27Mar 24Mar 21Mar 18Mar 15Mar 12Mar 8Mar 4

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 23Sep 27Oct 1Oct 3Oct 5Oct 8Oct 12Oct 15Oct 20
32°FOct 2Oct 8Oct 12Oct 15Oct 18Oct 20Oct 23Oct 26Oct 31
28°FOct 15Oct 20Oct 24Oct 26Oct 29Oct 31Nov 2Nov 5Nov 10
24°FOct 27Oct 31Nov 2Nov 4Nov 7Nov 10Nov 13Nov 17Nov 21
20°FNov 2Nov 7Nov 11Nov 14Nov 16Nov 19Nov 22Nov 26Dec 1
16°FNov 10Nov 15Nov 19Nov 22Nov 24Nov 27Dec 1Dec 4Dec 11

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°F171165160156153150145140134
32°F193185181176173169165160153
28°F216208204199195192187182175
24°F236229224220217212209204197
20°F255248243238234231227221216
16°F273266261256252248244238232

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
7,125
Cooling degree days, base 65°F
678
Growing degree days, base 40°F
4,774
Growing degree days, base 45°F
3,709
Growing degree days, base 50°F
2,769
Growing degree days, base 55°F
1,949
Growing degree days, base 60°F
1,246

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,42900
February1,18701
March966115
April575263
May24338283
June38142554
July7236694
August13187638
September13465387
October4598121
November846013
December1,22901

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 1.3 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 USC00474108 (Jefferson Wwtp). Public domain.