Smithfield climate

Smithfield Frost Dates and Growing Season

NOAA 1991-2020 normals for Richmond, 7.8 km from Smithfield, elevation 4680 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Richmond. 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 May 11 and the first fall freeze around October 5, a growing season of about 143 days.

Median at 36°F
last May 31, first September 24
Median at 32°F
last May 11, first October 5
Median at 28°F
last April 26, first October 17

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°FJun 15Jun 10Jun 7Jun 3May 31May 27May 22May 18May 12
32°FJun 2May 25May 20May 15May 11May 8May 5May 2Apr 27
28°FMay 13May 7May 3Apr 29Apr 26Apr 23Apr 19Apr 14Apr 8
24°FApr 28Apr 20Apr 15Apr 10Apr 6Apr 3Mar 31Mar 26Mar 17
20°FApr 9Apr 2Mar 29Mar 23Mar 17Mar 13Mar 10Mar 6Mar 2
16°FMar 24Mar 15Mar 11Mar 8Mar 5Mar 2Feb 28Feb 25Feb 18

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 10Sep 15Sep 19Sep 21Sep 24Sep 27Sep 30Oct 3Oct 7
32°FSep 21Sep 26Sep 30Oct 2Oct 5Oct 7Oct 11Oct 15Oct 20
28°FOct 1Oct 5Oct 10Oct 14Oct 17Oct 20Oct 23Oct 27Nov 1
24°FOct 13Oct 19Oct 23Oct 26Oct 29Nov 1Nov 4Nov 8Nov 13
20°FOct 24Oct 29Nov 1Nov 5Nov 9Nov 12Nov 15Nov 19Nov 24
16°FNov 2Nov 8Nov 12Nov 15Nov 18Nov 23Nov 26Nov 29Dec 4

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°F13913012311911611110710194
32°F164157152148143138133128120
28°F195187181176172168164158149
24°F228219213207201197191185177
20°F255248242237233227222215206
16°F279271266262257253248241233

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
6,908
Cooling degree days, base 65°F
573
Growing degree days, base 40°F
4,450
Growing degree days, base 45°F
3,369
Growing degree days, base 50°F
2,451
Growing degree days, base 55°F
1,693
Growing degree days, base 60°F
1,067

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28000
February1,02600
March81106
April572038
May3286181
June10767413
July8248705
August13208660
September14044363
October503182
November87604
December1,24400

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 7.8 km from Smithfield. 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 USC00427271 (Richmond). Public domain.