Rock County climate

Rock County Frost Dates and Growing Season

NOAA 1991-2020 normals for Newport, 22.2 km from Rock County, elevation 2230 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Newport. 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 6 and the first fall freeze around October 1, a growing season of about 147 days.

Median at 36°F
last May 15, first September 24
Median at 32°F
last May 6, first October 1
Median at 28°F
last April 26, first October 11

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 28May 24May 21May 18May 15May 12May 10May 7May 3
32°FMay 20May 14May 11May 8May 6May 3May 1Apr 28Apr 23
28°FMay 10May 5May 2Apr 29Apr 26Apr 23Apr 19Apr 16Apr 11
24°FMay 1Apr 26Apr 22Apr 18Apr 15Apr 13Apr 10Apr 7Apr 4
20°FApr 21Apr 16Apr 13Apr 9Apr 6Apr 4Apr 1Mar 28Mar 22
16°FApr 14Apr 8Apr 5Apr 1Mar 30Mar 26Mar 22Mar 17Mar 11

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 11Sep 16Sep 20Sep 22Sep 24Sep 27Sep 29Oct 2Oct 6
32°FSep 20Sep 24Sep 27Sep 29Oct 1Oct 4Oct 7Oct 10Oct 14
28°FSep 28Oct 2Oct 5Oct 8Oct 11Oct 14Oct 17Oct 20Oct 23
24°FOct 6Oct 12Oct 15Oct 18Oct 21Oct 23Oct 25Oct 28Nov 1
20°FOct 16Oct 21Oct 24Oct 27Oct 30Nov 1Nov 4Nov 7Nov 12
16°FOct 24Oct 29Nov 1Nov 4Nov 7Nov 9Nov 12Nov 16Nov 21

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°F147141138133130127123119113
32°F164159154151147144140136130
28°F184178173168164161157151146
24°F204197193189184181177170164
20°F222216211207202199195189182
16°F244235230225220216211205199

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
7,330
Cooling degree days, base 65°F
689
Growing degree days, base 40°F
4,649
Growing degree days, base 45°F
3,598
Growing degree days, base 50°F
2,676
Growing degree days, base 55°F
1,884
Growing degree days, base 60°F
1,221

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,35900
February1,13402
March944015
April604163
May29025244
June61123513
July10262717
August24206647
September16369369
October544494
November924012
December1,27101

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 22.2 km from Rock 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 USC00255925 (Newport). Public domain.