Grant County climate

Grant County Frost Dates and Growing Season

NOAA 1991-2020 normals for Petersburg, 12.9 km from Grant County, elevation 960 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 23 and the first fall freeze around October 20, a growing season of about 179 days.

Median at 36°F
last May 5, first October 10
Median at 32°F
last April 23, first October 20
Median at 28°F
last April 7, first October 30

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 22May 17May 12May 9May 5May 1Apr 28Apr 24Apr 19
32°FMay 13May 6May 1Apr 27Apr 23Apr 19Apr 15Apr 11Apr 5
28°FApr 30Apr 20Apr 15Apr 10Apr 7Apr 4Apr 1Mar 29Mar 23
24°FApr 8Apr 4Apr 1Mar 29Mar 26Mar 22Mar 19Mar 16Mar 9
20°FMar 29Mar 24Mar 20Mar 17Mar 14Mar 10Mar 6Mar 2Feb 25
16°FMar 19Mar 15Mar 11Mar 6Mar 3Feb 28Feb 24Feb 16Feb 8

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 28Oct 1Oct 5Oct 8Oct 10Oct 13Oct 15Oct 19Oct 24
32°FOct 8Oct 12Oct 15Oct 18Oct 20Oct 23Oct 26Oct 29Nov 2
28°FOct 15Oct 21Oct 25Oct 27Oct 30Nov 1Nov 5Nov 8Nov 13
24°FOct 25Oct 31Nov 2Nov 6Nov 9Nov 13Nov 17Nov 23Nov 30
20°FNov 4Nov 10Nov 15Nov 20Nov 25Nov 29Dec 2Dec 7Dec 15
16°FNov 17Nov 26Dec 1Dec 4Dec 9Dec 14Dec 18Dec 23Dec 30

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°F178172166162158154149142136
32°F201194188184179175170164155
28°F226219214210205200195190181
24°F255246240235230225221216209
20°F284274266260255249244237229
16°F308299293288283277271264254

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
4,795
Cooling degree days, base 65°F
1,060
Growing degree days, base 40°F
6,111
Growing degree days, base 45°F
4,793
Growing degree days, base 50°F
3,634
Growing degree days, base 55°F
2,622
Growing degree days, base 60°F
1,766

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January96909
February805012
March669255
April34817184
May14575401
June21216645
July1334798
August3279741
September55124520
October31113207
November607149
December863014

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 12.9 km from Grant County. 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 USC00466952 (Petersburg). Public domain.