Franklin County climate

Franklin County Frost Dates and Growing Season

NOAA 1991-2020 normals for Mt Vernon, 2.3 km from Franklin County, elevation 447 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mt Vernon. 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 15 and the first fall freeze around November 16, a growing season of about 245 days.

Median at 36°F
last March 31, first November 4
Median at 32°F
last March 15, first November 16
Median at 28°F
last March 2, first December 1

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 3Mar 31Mar 26Mar 21Mar 16Mar 8
32°FApr 6Mar 31Mar 25Mar 20Mar 15Mar 11Mar 6Mar 1Feb 23
28°FMar 25Mar 15Mar 10Mar 6Mar 2Feb 27Feb 21Feb 15Feb 4
24°FMar 12Mar 5Feb 28Feb 22Feb 14Feb 7Feb 1Jan 25Jan 13
20°FMar 2Feb 16Feb 8Feb 2Jan 29Jan 23Jan 15Jan 6Dec 28
16°FFeb 16Feb 7Jan 31Jan 26Jan 17Jan 9Jan 4Dec 29Dec 21

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

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°F247238230225220214209203195
32°F272264257250245241234226217
28°F303293286279273267260251242
24°F341330322313306300292284270
20°F365365357346340334327318304
16°F365365365365365362353342331

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
98% of years
20°F or colder
80% of years
16°F or colder
44% 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
2,511
Cooling degree days, base 65°F
2,413
Growing degree days, base 40°F
9,173
Growing degree days, base 45°F
7,533
Growing degree days, base 50°F
6,021
Growing degree days, base 55°F
4,656
Growing degree days, base 60°F
3,452

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January625262
February4556100
March29526244
April11575415
May20230676
June0441891
July05751,040
August05661,031
September8351793
October100117487
November32721203
December567479

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 2.3 km from Franklin 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 USC00416119 (Mt Vernon). Public domain.