Union climate

Union Frost Dates and Growing Season

NOAA 1991-2020 normals for Cushman Powerhouse #2, 4.8 km from Union, elevation 21 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cushman Powerhouse #2. 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 March 24 and the first fall freeze around November 15, a growing season of about 235 days.

Median at 36°F
last April 22, first October 28
Median at 32°F
last March 24, first November 15
Median at 28°F
last February 20, first December 7

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 8May 2Apr 29Apr 26Apr 22Apr 18Apr 14Apr 9Apr 2
32°FApr 17Apr 9Apr 2Mar 29Mar 24Mar 19Mar 13Mar 5Feb 26
28°FMar 17Mar 7Mar 1Feb 25Feb 20Feb 16Feb 8Jan 27Jan 4
24°FFeb 21Feb 15Feb 3Jan 25Jan 11Dec 31Dec 23Dec 14Dec 5
20°FFeb 20Feb 17Feb 7Jan 22Jan 1Dec 24Dec 15Dec 9Nov 30
16°F–––––––––

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°FOct 11Oct 17Oct 21Oct 25Oct 28Oct 31Nov 3Nov 8Nov 15
32°FOct 25Nov 1Nov 5Nov 10Nov 15Nov 20Nov 25Dec 1Dec 8
28°FNov 9Nov 21Nov 27Dec 2Dec 7Dec 12Dec 20Dec 28Jan 13
24°FNov 26Dec 3Dec 9Dec 15Dec 22Dec 30Jan 5Jan 24Feb 12
20°FNov 30Dec 6Dec 11Dec 18Dec 29Jan 6Feb 1Feb 15Feb 20
16°F–––––––––

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°F212204198192187183178172164
32°F269255248240235229222216207
28°F340321311302294286278268255
24°F365365365364353344334324311
20°F365365365365365365365365337
16°F365365365365365365365365365

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
98% of years
24°F or colder
66% of years
20°F or colder
19% of years
16°F or colder
1% 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
5,106
Cooling degree days, base 65°F
123
Growing degree days, base 40°F
4,331
Growing degree days, base 45°F
2,918
Growing degree days, base 50°F
1,831
Growing degree days, base 55°F
1,016
Growing degree days, base 60°F
438

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January76001
February65501
March625010
April483045
May2963184
June16914296
July5851459
August5547457
September1707289
October428080
November62609
December78401

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 4.8 km from Union. 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 USC00451939 (Cushman Powerhouse #2). Public domain.