Petersburg climate

Petersburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Petersburg, 1.5 km from Petersburg, elevation 19 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Petersburg. 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 3 and the first fall freeze around November 3, a growing season of about 216 days.

Median at 36°F
last April 16, first October 26
Median at 32°F
last April 3, first November 3
Median at 28°F
last March 20, first November 16

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

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°F213206202198193190185180172
32°F236229224219216212208203196
28°F263255249244239235230225217
24°F296287279274267262257252245
20°F327317309304298292284277268
16°F364350339333326318311305296

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
90% 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
3,759
Cooling degree days, base 65°F
1,525
Growing degree days, base 40°F
7,259
Growing degree days, base 45°F
5,797
Growing degree days, base 50°F
4,497
Growing degree days, base 55°F
3,347
Growing degree days, base 60°F
2,355

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January815021
February682027
March529698
April24333263
May70120515
June4299746
July0439904
August0383848
September20204634
October20039316
November471396
December726030

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 1.5 km from Petersburg. 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 USC00446656 (Petersburg). Public domain.