Jefferson County climate

Jefferson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Madison Sewage Plt, 6.7 km from Jefferson County, elevation 460 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Madison Sewage Plt. 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 11 and the first fall freeze around October 31, a growing season of about 201 days.

Median at 36°F
last April 22, first October 21
Median at 32°F
last April 11, first October 31
Median at 28°F
last March 31, first November 10

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 8May 2Apr 29Apr 25Apr 22Apr 20Apr 17Apr 13Apr 9
32°FApr 28Apr 22Apr 18Apr 15Apr 11Apr 9Apr 6Apr 3Mar 28
28°FApr 16Apr 10Apr 6Apr 2Mar 31Mar 29Mar 25Mar 20Mar 16
24°FApr 7Apr 1Mar 28Mar 24Mar 20Mar 17Mar 13Mar 8Mar 1
20°FMar 28Mar 21Mar 17Mar 12Mar 9Mar 5Mar 1Feb 26Feb 19
16°FMar 17Mar 11Mar 7Mar 3Feb 28Feb 25Feb 19Feb 13Feb 7

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 6Oct 12Oct 15Oct 18Oct 21Oct 23Oct 25Oct 29Nov 1
32°FOct 15Oct 22Oct 25Oct 29Oct 31Nov 2Nov 4Nov 8Nov 14
28°FOct 29Nov 1Nov 3Nov 6Nov 10Nov 13Nov 17Nov 21Nov 29
24°FNov 4Nov 9Nov 14Nov 17Nov 21Nov 26Dec 1Dec 4Dec 12
20°FNov 12Nov 18Nov 25Nov 30Dec 3Dec 6Dec 11Dec 19Dec 25
16°FNov 24Dec 1Dec 6Dec 11Dec 17Dec 21Dec 26Dec 31Jan 7

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°F198191186182179175171166160
32°F221213209205201197192186179
28°F247239234228223218214208201
24°F272264259252247243237231222
20°F296287280274270264259253242
16°F316307301297292287280273263

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
4,532
Cooling degree days, base 65°F
1,288
Growing degree days, base 40°F
6,586
Growing degree days, base 45°F
5,240
Growing degree days, base 50°F
4,038
Growing degree days, base 55°F
2,979
Growing degree days, base 60°F
2,062

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January99206
February82208
March629153
April29715216
May9096472
June8257699
July1374839
August1342806
September34173590
October24728272
November566165
December847014

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 6.7 km from Jefferson County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00125237 (Madison Sewage Plt). Public domain.