Winthrop climate

Winthrop Frost Dates and Growing Season

NOAA 1991-2020 normals for Independence #1, 13.2 km from Winthrop, elevation 1010 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Independence #1. 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 30 and the first fall freeze around October 7, a growing season of about 159 days.

Median at 36°F
last May 9, first September 29
Median at 32°F
last April 30, first October 7
Median at 28°F
last April 20, 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 22May 17May 14May 11May 9May 6May 3Apr 30Apr 26
32°FMay 12May 8May 5May 2Apr 30Apr 28Apr 25Apr 21Apr 16
28°FMay 4Apr 30Apr 26Apr 23Apr 20Apr 17Apr 14Apr 9Apr 5
24°FApr 25Apr 20Apr 15Apr 12Apr 9Apr 6Apr 4Apr 1Mar 26
20°FApr 14Apr 8Apr 5Apr 3Apr 1Mar 30Mar 25Mar 21Mar 15
16°FApr 5Apr 1Mar 29Mar 26Mar 22Mar 19Mar 16Mar 12Mar 7

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 19Sep 22Sep 26Sep 29Oct 1Oct 4Oct 8Oct 12
32°FSep 23Sep 27Oct 1Oct 3Oct 7Oct 10Oct 13Oct 16Oct 21
28°FOct 2Oct 8Oct 12Oct 15Oct 17Oct 20Oct 23Oct 26Oct 31
24°FOct 13Oct 19Oct 22Oct 25Oct 27Oct 29Nov 1Nov 3Nov 9
20°FOct 22Oct 27Oct 30Nov 1Nov 4Nov 6Nov 10Nov 14Nov 20
16°FNov 1Nov 4Nov 7Nov 10Nov 14Nov 17Nov 20Nov 24Dec 1

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°F160154150146142139135130123
32°F178171167163159156152147141
28°F198191188184179176171166160
24°F218212207204200196191187180
20°F238231226221218213209204197
16°F257249244239235231227222214

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
7,252
Cooling degree days, base 65°F
723
Growing degree days, base 40°F
4,864
Growing degree days, base 45°F
3,803
Growing degree days, base 50°F
2,856
Growing degree days, base 55°F
2,023
Growing degree days, base 60°F
1,304

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,48000
February1,22500
March960014
April536478
May21740308
June29174595
July6236694
August18185632
September13976395
October4727123
November878016
December1,29301

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 13.2 km from Winthrop. 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 USC00134049 (Independence #1). Public domain.