Blacksburg climate

Blacksburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Ninety Nine Is, 10.2 km from Blacksburg, elevation 500 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ninety Nine Is. 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 20 and the first fall freeze around October 24, a growing season of about 186 days.

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

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 4Oct 7Oct 10Oct 13Oct 15Oct 18Oct 21Oct 24Oct 29
32°FOct 11Oct 15Oct 18Oct 21Oct 24Oct 27Oct 30Nov 1Nov 5
28°FOct 20Oct 24Oct 28Oct 31Nov 1Nov 4Nov 7Nov 11Nov 16
24°FOct 30Nov 2Nov 5Nov 9Nov 12Nov 16Nov 19Nov 24Dec 1
20°FNov 6Nov 12Nov 17Nov 21Nov 25Nov 29Dec 3Dec 8Dec 20
16°FNov 19Nov 25Dec 1Dec 5Dec 10Dec 19Dec 27Jan 2Jan 11

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°F188181176172168164160156148
32°F209201195191186182178173165
28°F233225219214210206201195187
24°F262252244239234229224218210
20°F294283274267261256251244237
16°F330318307301295288280272261

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
99% 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
3,789
Cooling degree days, base 65°F
1,235
Growing degree days, base 40°F
6,890
Growing degree days, base 45°F
5,421
Growing degree days, base 50°F
4,124
Growing degree days, base 55°F
2,997
Growing degree days, base 60°F
2,033

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January815014
February641023
March505188
April25015237
May7586477
June6244688
July0364829
August0331795
September27165588
October22127288
November514171
December733026

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 10.2 km from Blacksburg. 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 USC00386293 (Ninety Nine Is). Public domain.