Montgomery County climate

Montgomery County Frost Dates and Growing Season

NOAA 1991-2020 normals for Blacksburg Nwso, 4.1 km from Montgomery County, elevation 2103 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Blacksburg Nwso. 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 24 and the first fall freeze around October 19, a growing season of about 175 days.

Median at 36°F
last May 6, first October 8
Median at 32°F
last April 24, first October 19
Median at 28°F
last April 11, first October 29

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 24May 18May 14May 10May 6May 3Apr 30Apr 25Apr 21
32°FMay 14May 7May 1Apr 28Apr 24Apr 21Apr 19Apr 15Apr 11
28°FApr 27Apr 21Apr 17Apr 14Apr 11Apr 9Apr 6Apr 2Mar 28
24°FApr 13Apr 8Apr 4Apr 1Mar 30Mar 27Mar 24Mar 19Mar 14
20°FApr 1Mar 28Mar 24Mar 20Mar 17Mar 13Mar 10Mar 5Feb 27
16°FMar 22Mar 17Mar 12Mar 8Mar 3Feb 28Feb 24Feb 16Feb 9

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°FSep 26Oct 1Oct 3Oct 6Oct 8Oct 11Oct 13Oct 17Oct 21
32°FOct 6Oct 10Oct 14Oct 16Oct 19Oct 22Oct 25Oct 28Nov 1
28°FOct 15Oct 20Oct 23Oct 26Oct 29Nov 1Nov 2Nov 5Nov 8
24°FOct 24Oct 29Nov 1Nov 3Nov 5Nov 8Nov 12Nov 15Nov 22
20°FNov 1Nov 6Nov 10Nov 14Nov 17Nov 20Nov 25Dec 1Dec 7
16°FNov 12Nov 18Nov 24Nov 30Dec 2Dec 6Dec 12Dec 19Dec 28

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°F173167162159155150146141134
32°F196189184181175172168162154
28°F218212207203199196191187178
24°F243236230225220216213208203
20°F271263256250245240235229221
16°F306296289282276270264256247

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
5,295
Cooling degree days, base 65°F
619
Growing degree days, base 40°F
5,327
Growing degree days, base 45°F
4,067
Growing degree days, base 50°F
2,974
Growing degree days, base 55°F
2,033
Growing degree days, base 60°F
1,245

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02803
February84806
March722034
April4113132
May18332327
June34121537
July5211671
August10175631
September8969433
October3717160
November668033
December92707

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 4.1 km from Montgomery 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 USC00440766 (Blacksburg Nwso). Public domain.