Williamsburg climate

Williamsburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Raystown Lake 2, 13.8 km from Williamsburg, elevation 1000 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Raystown Lake 2. 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 19 and the first fall freeze around October 28, a growing season of about 191 days.

Median at 36°F
last April 30, first October 15
Median at 32°F
last April 19, first October 28
Median at 28°F
last April 6, first November 9

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 18May 11May 8May 4Apr 30Apr 28Apr 24Apr 21Apr 17
32°FMay 7May 1Apr 26Apr 22Apr 19Apr 16Apr 12Apr 9Apr 5
28°FApr 19Apr 14Apr 10Apr 8Apr 6Apr 3Apr 1Mar 30Mar 24
24°FApr 8Apr 4Apr 1Mar 30Mar 27Mar 23Mar 20Mar 16Mar 11
20°FMar 29Mar 25Mar 22Mar 19Mar 16Mar 12Mar 9Mar 4Feb 27
16°FMar 22Mar 17Mar 14Mar 9Mar 6Mar 3Feb 28Feb 23Feb 14

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 12Oct 15Oct 18Oct 22Oct 26Oct 31
32°FOct 12Oct 18Oct 22Oct 25Oct 28Nov 1Nov 3Nov 5Nov 10
28°FOct 26Nov 1Nov 4Nov 6Nov 9Nov 12Nov 15Nov 18Nov 23
24°FNov 7Nov 11Nov 14Nov 17Nov 20Nov 24Nov 27Dec 1Dec 8
20°FNov 17Nov 23Nov 28Dec 1Dec 5Dec 10Dec 15Dec 20Dec 26
16°FDec 1Dec 7Dec 12Dec 17Dec 21Dec 25Dec 29Jan 1Jan 9

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°F187180175171167161157152144
32°F211205200195191185181175167
28°F236229224219216212208203195
24°F262254249245241236233228220
20°F290282276271266261256250242
16°F312305299294289284280274265

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
5,558
Cooling degree days, base 65°F
840
Growing degree days, base 40°F
5,468
Growing degree days, base 45°F
4,257
Growing degree days, base 50°F
3,189
Growing degree days, base 55°F
2,263
Growing degree days, base 60°F
1,479

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,11003
February95102
March807126
April4397119
May17645341
June33159576
July2281744
August4244705
September7895468
October35410169
November653031
December95306

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 13.8 km from Williamsburg. 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 USC00367312 (Raystown Lake 2). Public domain.