Elroy climate

Elroy Frost Dates and Growing Season

NOAA 1991-2020 normals for Hillsboro, 10.9 km from Elroy, elevation 940 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hillsboro. 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 5 and the first fall freeze around October 4, a growing season of about 153 days.

Median at 36°F
last May 16, first September 27
Median at 32°F
last May 5, first October 4
Median at 28°F
last April 23, 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°FMay 30May 25May 22May 19May 16May 13May 10May 7May 3
32°FMay 18May 14May 11May 8May 5May 2Apr 30Apr 26Apr 22
28°FMay 7May 2Apr 29Apr 26Apr 23Apr 20Apr 16Apr 13Apr 9
24°FApr 27Apr 22Apr 18Apr 14Apr 11Apr 8Apr 5Apr 2Mar 29
20°FApr 17Apr 11Apr 7Apr 4Apr 2Mar 31Mar 27Mar 23Mar 17
16°FApr 6Apr 1Mar 30Mar 27Mar 24Mar 21Mar 17Mar 13Mar 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 14Sep 19Sep 21Sep 24Sep 27Sep 29Oct 1Oct 3Oct 8
32°FSep 23Sep 27Sep 30Oct 2Oct 4Oct 7Oct 9Oct 13Oct 18
28°FOct 2Oct 7Oct 11Oct 14Oct 17Oct 20Oct 23Oct 27Nov 1
24°FOct 15Oct 20Oct 23Oct 26Oct 28Oct 31Nov 2Nov 6Nov 12
20°FOct 28Nov 1Nov 2Nov 5Nov 8Nov 11Nov 15Nov 19Nov 24
16°FNov 3Nov 7Nov 12Nov 15Nov 18Nov 22Nov 24Nov 28Dec 3

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°F151145140136133128125120114
32°F173166161157153149145140135
28°F196189184180176172168163157
24°F220213208204201196192187180
20°F242233229225220216212208201
16°F260253248242238234230225218

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
7,454
Cooling degree days, base 65°F
581
Growing degree days, base 40°F
4,537
Growing degree days, base 45°F
3,495
Growing degree days, base 50°F
2,574
Growing degree days, base 55°F
1,777
Growing degree days, base 60°F
1,107

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,48900
February1,22900
March98909
April575367
May26327256
June55125521
July11208662
August24161603
September16350347
October508696
November867012
December1,28201

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 10.9 km from Elroy. 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 USC00473654 (Hillsboro). Public domain.