Jefferson County climate

Jefferson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Port Gibson 1 Ne, 28.6 km from Jefferson County, elevation 120 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Port Gibson 1 Ne. 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 March 17 and the first fall freeze around November 12, a growing season of about 241 days.

Median at 36°F
last March 31, first November 2
Median at 32°F
last March 17, first November 12
Median at 28°F
last March 1, first November 25

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 19Apr 12Apr 7Apr 4Mar 31Mar 28Mar 25Mar 19Mar 12
32°FApr 7Apr 1Mar 27Mar 21Mar 17Mar 12Mar 7Mar 2Feb 24
28°FMar 22Mar 14Mar 9Mar 5Mar 1Feb 26Feb 21Feb 15Feb 3
24°FMar 11Mar 4Feb 27Feb 22Feb 15Feb 10Feb 3Jan 29Jan 15
20°FMar 1Feb 20Feb 10Feb 4Jan 31Jan 27Jan 18Jan 9Dec 30
16°FFeb 18Feb 7Feb 2Jan 30Jan 23Jan 18Jan 12Jan 6Dec 30

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 20Oct 24Oct 28Oct 31Nov 2Nov 4Nov 7Nov 11Nov 17
32°FOct 29Nov 2Nov 5Nov 8Nov 12Nov 15Nov 20Nov 24Dec 1
28°FNov 5Nov 11Nov 16Nov 21Nov 25Nov 30Dec 5Dec 10Dec 27
24°FNov 15Nov 24Dec 1Dec 6Dec 13Dec 25Jan 1Jan 6Jan 18
20°FDec 4Dec 12Dec 25Jan 1Jan 4Jan 9Jan 15Jan 25Feb 5
16°FDec 20Dec 31Jan 4Jan 7Jan 11Jan 16Jan 26Feb 1Feb 14

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°F242234227222217212207202194
32°F271261253246241235229222213
28°F305294285278271264258251241
24°F339329321313306298290280267
20°F365365361350340334328317304
16°F365365365365365365357344333

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
97% of years
20°F or colder
75% of years
16°F or colder
36% 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
2,163
Cooling degree days, base 65°F
2,470
Growing degree days, base 40°F
9,517
Growing degree days, base 45°F
7,829
Growing degree days, base 50°F
6,266
Growing degree days, base 55°F
4,844
Growing degree days, base 60°F
3,572

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January546695
February4049125
March24138294
April95102459
May13267719
June0444894
July05381,003
August0532997
September3369816
October84134518
November29624223
December4809122

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 28.6 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 USC00227132 (Port Gibson 1 Ne). Public domain.