Grant County climate

Grant County Frost Dates and Growing Season

NOAA 1991-2020 normals for Jefferson 3SE, 12.7 km from Grant County, elevation 1043 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jefferson 3SE. 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 18 and the first fall freeze around October 20, a growing season of about 183 days.

Median at 36°F
last April 29, first October 11
Median at 32°F
last April 18, first October 20
Median at 28°F
last April 9, first October 28

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 10May 5May 3Apr 30Apr 29Apr 26Apr 22Apr 18Apr 13
32°FMay 2Apr 29Apr 24Apr 21Apr 18Apr 15Apr 12Apr 9Apr 4
28°FApr 23Apr 18Apr 15Apr 12Apr 9Apr 5Apr 3Mar 31Mar 25
24°FApr 15Apr 9Apr 5Apr 2Mar 30Mar 26Mar 21Mar 16Mar 9
20°FApr 3Mar 31Mar 26Mar 22Mar 17Mar 13Mar 9Mar 5Feb 28
16°FMar 25Mar 17Mar 13Mar 10Mar 6Mar 2Feb 28Feb 23Feb 15

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 27Oct 1Oct 5Oct 8Oct 11Oct 14Oct 16Oct 19Oct 23
32°FOct 4Oct 10Oct 14Oct 17Oct 20Oct 22Oct 25Oct 28Nov 2
28°FOct 14Oct 20Oct 23Oct 26Oct 28Nov 1Nov 3Nov 7Nov 11
24°FOct 23Oct 28Nov 1Nov 3Nov 6Nov 9Nov 12Nov 17Nov 23
20°FOct 29Nov 4Nov 8Nov 11Nov 15Nov 19Nov 23Nov 28Dec 3
16°FNov 5Nov 13Nov 17Nov 21Nov 26Nov 30Dec 3Dec 7Dec 14

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°F184177174169166162158154147
32°F203197191187183179175170164
28°F224215210206202198194189181
24°F245237232227222217213208202
20°F267258252247242237232226218
16°F291281274268263259253248238

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
4,409
Cooling degree days, base 65°F
1,705
Growing degree days, base 40°F
7,104
Growing degree days, base 45°F
5,740
Growing degree days, base 50°F
4,528
Growing degree days, base 55°F
3,451
Growing degree days, base 60°F
2,511

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January96404
February762018
March567384
April28619224
May78125513
June3345792
July0504969
August0456921
September35215631
October23638297
November576168
December90208

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 12.7 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 USC00344573 (Jefferson 3SE). Public domain.