Union climate

Union Frost Dates and Growing Season

NOAA 1991-2020 normals for Union 3 Sse, 5.5 km from Union, elevation 2110 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Union 3 Sse. 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 12, a growing season of about 165 days.

Median at 36°F
last May 10, first October 4
Median at 32°F
last April 30, first October 12
Median at 28°F
last April 15, first October 22

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 26May 20May 16May 13May 10May 6May 3Apr 30Apr 24
32°FMay 17May 11May 6May 2Apr 30Apr 25Apr 21Apr 17Apr 12
28°FMay 6Apr 29Apr 22Apr 18Apr 15Apr 11Apr 7Apr 4Mar 31
24°FApr 16Apr 11Apr 6Apr 4Apr 1Mar 30Mar 26Mar 22Mar 16
20°FApr 6Apr 1Mar 28Mar 24Mar 20Mar 17Mar 13Mar 8Mar 1
16°FMar 27Mar 21Mar 17Mar 13Mar 8Mar 5Mar 1Feb 25Feb 16

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 20Sep 25Sep 29Oct 1Oct 4Oct 6Oct 9Oct 12Oct 16
32°FSep 30Oct 4Oct 7Oct 10Oct 12Oct 15Oct 18Oct 22Oct 26
28°FOct 9Oct 12Oct 16Oct 19Oct 22Oct 25Oct 28Nov 1Nov 5
24°FOct 15Oct 21Oct 25Oct 28Nov 1Nov 3Nov 5Nov 10Nov 14
20°FOct 26Nov 1Nov 4Nov 8Nov 11Nov 15Nov 19Nov 23Dec 1
16°FNov 4Nov 12Nov 17Nov 21Nov 26Nov 30Dec 5Dec 11Dec 20

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°F168159155150147142138133125
32°F187180175170165160155148141
28°F211203198194188184179173163
24°F234227221216212208204198190
20°F260251245240235230225219211
16°F295283275269262257251244234

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
5,137
Cooling degree days, base 65°F
725
Growing degree days, base 40°F
5,563
Growing degree days, base 45°F
4,287
Growing degree days, base 50°F
3,164
Growing degree days, base 55°F
2,196
Growing degree days, base 60°F
1,381

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,01306
February83205
March698147
April3849161
May16746353
June28152574
July3234696
August6200659
September8675442
October3627170
November650145
December90808

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 5.5 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 USC00469011 (Union 3 Sse). Public domain.