Zion climate

Zion Frost Dates and Growing Season

NOAA 1991-2020 normals for Millheim, 17.9 km from Zion, elevation 1120 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Millheim. 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 5 and the first fall freeze around October 6, a growing season of about 153 days.

Median at 36°F
last May 19, first September 27
Median at 32°F
last May 5, first October 6
Median at 28°F
last April 24, first October 18

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 31May 28May 25May 21May 19May 14May 11May 7May 1
32°FMay 24May 19May 14May 9May 5May 2Apr 29Apr 26Apr 22
28°FMay 13May 7May 1Apr 28Apr 24Apr 22Apr 18Apr 15Apr 11
24°FApr 27Apr 21Apr 17Apr 15Apr 12Apr 9Apr 5Apr 2Mar 29
20°FApr 13Apr 8Apr 5Apr 1Mar 31Mar 28Mar 25Mar 21Mar 16
16°FApr 2Mar 30Mar 27Mar 24Mar 21Mar 18Mar 15Mar 10Mar 5

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 14Sep 20Sep 22Sep 24Sep 27Sep 29Oct 1Oct 4Oct 8
32°FSep 25Sep 28Oct 1Oct 3Oct 6Oct 9Oct 12Oct 16Oct 21
28°FOct 4Oct 8Oct 12Oct 15Oct 18Oct 22Oct 25Oct 30Nov 3
24°FOct 14Oct 20Oct 25Oct 29Nov 1Nov 3Nov 6Nov 10Nov 14
20°FOct 29Nov 3Nov 6Nov 9Nov 13Nov 16Nov 20Nov 24Dec 1
16°FNov 9Nov 14Nov 18Nov 21Nov 26Nov 30Dec 3Dec 8Dec 15

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°F152146140136132128124119112
32°F175167162157153149145140132
28°F199192185181176172167162155
24°F224217212208203199194188179
20°F248241236232228224219215206
16°F274265259254249244239235229

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
6,659
Cooling degree days, base 65°F
535
Growing degree days, base 40°F
4,614
Growing degree days, base 45°F
3,525
Growing degree days, base 50°F
2,568
Growing degree days, base 55°F
1,748
Growing degree days, base 60°F
1,068

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28800
February1,06401
March925011
April536276
May24426268
June52112510
July9200656
August22146589
September15446346
October4784100
November79409
December1,09301

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 17.9 km from Zion. 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 USC00365790 (Millheim). Public domain.