Shafer climate

Shafer Frost Dates and Growing Season

NOAA 1991-2020 normals for St Croix Falls, 8.4 km from Shafer, elevation 750 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for St Croix Falls. 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 4 and the first fall freeze around October 8, a growing season of about 156 days.

Median at 36°F
last May 14, first September 29
Median at 32°F
last May 4, first October 8
Median at 28°F
last April 24, first October 20

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 27May 23May 20May 16May 14May 11May 7May 5Apr 30
32°FMay 18May 14May 9May 6May 4May 1Apr 29Apr 25Apr 20
28°FMay 8May 4Apr 30Apr 28Apr 24Apr 22Apr 18Apr 14Apr 9
24°FApr 30Apr 25Apr 21Apr 17Apr 14Apr 10Apr 8Apr 5Apr 1
20°FApr 21Apr 14Apr 10Apr 8Apr 5Apr 3Apr 1Mar 29Mar 22
16°FApr 11Apr 8Apr 4Apr 1Mar 30Mar 27Mar 22Mar 19Mar 13

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 15Sep 20Sep 23Sep 26Sep 29Oct 1Oct 4Oct 8Oct 12
32°FSep 24Sep 29Oct 1Oct 5Oct 8Oct 11Oct 14Oct 18Oct 23
28°FOct 3Oct 10Oct 13Oct 17Oct 20Oct 22Oct 26Oct 30Nov 2
24°FOct 18Oct 23Oct 26Oct 29Oct 31Nov 2Nov 4Nov 7Nov 12
20°FOct 28Oct 31Nov 3Nov 5Nov 8Nov 11Nov 14Nov 17Nov 22
16°FNov 2Nov 6Nov 9Nov 12Nov 15Nov 18Nov 21Nov 24Nov 29

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°F155150145141137133129125119
32°F175168164159156153148144135
28°F197190185181177173169163154
24°F217210205201197193189184177
20°F237230225220215212207202196
16°F250244239235231227223218210

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
8,122
Cooling degree days, base 65°F
576
Growing degree days, base 40°F
4,414
Growing degree days, base 45°F
3,413
Growing degree days, base 50°F
2,525
Growing degree days, base 55°F
1,749
Growing degree days, base 60°F
1,096

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,61600
February1,35500
March1,09306
April627252
May28028248
June58118510
July12207660
August23160601
September16556353
October537587
November95707
December1,40000

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 8.4 km from Shafer. 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 USC00477464 (St Croix Falls). Public domain.