Rappahannock County climate

Rappahannock County Frost Dates and Growing Season

NOAA 1991-2020 normals for Sperryville, 6.8 km from Rappahannock County, elevation 750 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sperryville. 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 16 and the first fall freeze around October 27, a growing season of about 192 days.

Median at 36°F
last April 30, first October 15
Median at 32°F
last April 16, first October 27
Median at 28°F
last April 2, first November 5

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

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°F188181176172168163159153147
32°F213207202197192187182177169
28°F237230225221217214209203196
24°F266258252247242237232227221
20°F295285278272267263258252244
16°F323311304298293287282275266

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
4,810
Cooling degree days, base 65°F
894
Growing degree days, base 40°F
5,890
Growing degree days, base 45°F
4,572
Growing degree days, base 50°F
3,412
Growing degree days, base 55°F
2,413
Growing degree days, base 60°F
1,576

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January97007
February80609
March695139
April36612157
May15548362
June19172603
July1292756
August3251713
September59104496
October30614207
November572053
December859010

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 6.8 km from Rappahannock 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 USC00447985 (Sperryville). Public domain.