Rockbridge County climate

Rockbridge County Frost Dates and Growing Season

NOAA 1991-2020 normals for Lexington, 4.3 km from Rockbridge County, elevation 1097 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Lexington. 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 23 and the first fall freeze around October 23, a growing season of about 181 days.

Median at 36°F
last May 4, first October 13
Median at 32°F
last April 23, first October 23
Median at 28°F
last April 9, first November 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°FMay 20May 14May 11May 7May 4May 1Apr 28Apr 23Apr 18
32°FMay 11May 5May 1Apr 26Apr 23Apr 19Apr 16Apr 13Apr 8
28°FApr 26Apr 19Apr 15Apr 12Apr 9Apr 6Apr 2Mar 31Mar 25
24°FApr 10Apr 5Apr 2Mar 31Mar 28Mar 24Mar 20Mar 16Mar 9
20°FApr 1Mar 27Mar 23Mar 19Mar 15Mar 10Mar 6Mar 1Feb 24
16°FMar 21Mar 15Mar 9Mar 4Mar 1Feb 26Feb 21Feb 13Feb 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°FOct 1Oct 5Oct 8Oct 10Oct 13Oct 15Oct 18Oct 22Oct 26
32°FOct 9Oct 13Oct 17Oct 20Oct 23Oct 25Oct 28Oct 31Nov 3
28°FOct 17Oct 22Oct 26Oct 29Nov 1Nov 1Nov 4Nov 6Nov 11
24°FOct 27Nov 1Nov 2Nov 5Nov 8Nov 11Nov 14Nov 19Nov 25
20°FNov 4Nov 10Nov 13Nov 17Nov 21Nov 25Nov 30Dec 4Dec 12
16°FNov 16Nov 23Nov 30Dec 3Dec 8Dec 13Dec 19Dec 24Jan 1

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°F181175170165161157153148140
32°F201195190186181177173167158
28°F223216211207204199195189182
24°F249241236230227223218213207
20°F281272264258254249243236229
16°F312302295289282276269262254

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
4,661
Cooling degree days, base 65°F
1,020
Growing degree days, base 40°F
6,117
Growing degree days, base 45°F
4,783
Growing degree days, base 50°F
3,613
Growing degree days, base 55°F
2,596
Growing degree days, base 60°F
1,734

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January95306
February78308
March642148
April32911183
May12667410
June14202637
July0320784
August2281744
September54123519
October29516217
November605045
December857010

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 4.3 km from Rockbridge 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 USC00444876 (Lexington). Public domain.