Jefferson County climate

Jefferson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Monticello 10 Sw, 8.4 km from Jefferson County, elevation 219 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Monticello 10 Sw. 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 February 25 and the first fall freeze around December 3, a growing season of about 286 days.

Median at 36°F
last March 12, first November 18
Median at 32°F
last February 25, first December 3
Median at 28°F
last February 4, first December 27

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°FApr 1Mar 26Mar 20Mar 16Mar 12Mar 8Mar 4Feb 27Feb 18
32°FMar 17Mar 10Mar 5Mar 1Feb 25Feb 19Feb 12Feb 5Jan 25
28°FMar 5Feb 26Feb 18Feb 10Feb 4Jan 30Jan 24Jan 12Jan 1
24°FFeb 20Feb 9Feb 4Jan 31Jan 25Jan 18Jan 8Jan 1Dec 23
20°FFeb 11Feb 4Feb 1Jan 27Jan 20Jan 11Jan 6Dec 30Dec 22
16°F–––––––––

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°FNov 1Nov 7Nov 11Nov 14Nov 18Nov 22Nov 27Dec 2Dec 11
32°FNov 13Nov 19Nov 25Nov 30Dec 3Dec 7Dec 15Dec 26Jan 6
28°FNov 29Dec 4Dec 10Dec 19Dec 27Jan 2Jan 8Jan 17Jan 30
24°FDec 7Dec 16Dec 27Jan 1Jan 6Jan 13Jan 20Jan 30Feb 7
20°FDec 14Dec 24Dec 30Jan 6Jan 12Jan 19Jan 28Feb 2Feb 8
16°F–––––––––

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°F286274266259254249243236226
32°F321308300293286279272264253
28°F362343334328321313306297284
24°F365365365365357344335327316
20°F365365365365365365365363340
16°F365365365365365365365365365

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
90% of years
24°F or colder
58% of years
20°F or colder
24% of years
16°F or colder
2% 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
1,489
Cooling degree days, base 65°F
2,441
Growing degree days, base 40°F
10,106
Growing degree days, base 45°F
8,342
Growing degree days, base 50°F
6,654
Growing degree days, base 55°F
5,077
Growing degree days, base 60°F
3,657

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January40411165
February2847184
March17438342
April4991492
May4281742
June0427877
July0504969
August0491956
September1380829
October36165594
November18634312
December35112191

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 8.4 km from Jefferson County. 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 USC00085880 (Monticello 10 Sw). Public domain.