Siren climate

Siren Frost Dates and Growing Season

NOAA 1991-2020 normals for Grantsburg, 23.9 km from Siren, elevation 990 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Grantsburg. 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 11 and the first fall freeze around October 1, a growing season of about 141 days.

Median at 36°F
last May 23, first September 22
Median at 32°F
last May 11, first October 1
Median at 28°F
last April 30, 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°FJun 6Jun 1May 29May 26May 23May 20May 17May 13May 7
32°FMay 28May 23May 18May 14May 11May 8May 5May 1Apr 27
28°FMay 17May 11May 6May 2Apr 30Apr 27Apr 24Apr 20Apr 15
24°FMay 4Apr 30Apr 26Apr 22Apr 19Apr 17Apr 13Apr 9Apr 5
20°FApr 23Apr 19Apr 16Apr 13Apr 9Apr 6Apr 3Apr 1Mar 26
16°FApr 16Apr 11Apr 7Apr 4Apr 2Mar 31Mar 26Mar 22Mar 17

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 7Sep 12Sep 16Sep 19Sep 22Sep 25Sep 27Oct 1Oct 5
32°FSep 16Sep 21Sep 25Sep 28Oct 1Oct 3Oct 6Oct 10Oct 14
28°FSep 26Oct 1Oct 4Oct 7Oct 11Oct 14Oct 17Oct 21Oct 26
24°FOct 6Oct 12Oct 16Oct 20Oct 22Oct 26Oct 30Nov 2Nov 7
20°FOct 18Oct 23Oct 28Oct 31Nov 2Nov 5Nov 7Nov 11Nov 16
16°FOct 29Nov 1Nov 4Nov 7Nov 10Nov 13Nov 15Nov 19Nov 24

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°F14213412912412011511110597
32°F160153149145141136131126117
28°F182174170165161157152147140
24°F207200195190185180175170162
20°F225219215210207202198192185
16°F241236230226222219214209202

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
8,422
Cooling degree days, base 65°F
479
Growing degree days, base 40°F
4,172
Growing degree days, base 45°F
3,199
Growing degree days, base 50°F
2,339
Growing degree days, base 55°F
1,590
Growing degree days, base 60°F
964

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,65200
February1,35500
March1,10206
April658146
May29626236
June7295474
July18179626
August35131561
September19943312
October583472
November1,00506
December1,44600

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 23.9 km from Siren. 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 USW00014995 (Grantsburg). Public domain.