Iraan climate

Iraan Frost Dates and Growing Season

NOAA 1991-2020 normals for Sheffield, 26 km from Iraan, elevation 2175 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sheffield. 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 31 and the first fall freeze around November 3, a growing season of about 217 days.

Median at 36°F
last April 12, first October 27
Median at 32°F
last March 31, first November 3
Median at 28°F
last March 15, first November 12

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°FApr 30Apr 24Apr 19Apr 16Apr 12Apr 8Apr 4Mar 31Mar 24
32°FApr 19Apr 12Apr 6Apr 3Mar 31Mar 26Mar 21Mar 15Mar 10
28°FApr 5Mar 31Mar 24Mar 20Mar 15Mar 11Mar 7Mar 3Feb 26
24°FMar 22Mar 15Mar 9Mar 6Mar 2Feb 28Feb 23Feb 18Feb 12
20°FMar 11Mar 5Feb 28Feb 25Feb 19Feb 12Feb 7Feb 1Jan 24
16°FMar 1Feb 22Feb 14Feb 5Feb 1Jan 27Jan 20Jan 9Dec 21

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 9Oct 16Oct 20Oct 24Oct 27Oct 30Nov 1Nov 4Nov 9
32°FOct 20Oct 25Oct 28Nov 1Nov 3Nov 6Nov 9Nov 13Nov 17
28°FOct 27Nov 1Nov 5Nov 9Nov 12Nov 15Nov 18Nov 23Nov 28
24°FNov 5Nov 11Nov 16Nov 19Nov 23Nov 27Dec 1Dec 4Dec 11
20°FNov 18Nov 24Nov 28Dec 1Dec 5Dec 10Dec 16Dec 23Jan 1
16°FNov 28Dec 4Dec 8Dec 13Dec 21Dec 28Jan 3Jan 15Feb 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°F219211205200196191187181173
32°F242234228223217212207201194
28°F265257251245240235229221214
24°F292283276271265261256248240
20°F329316307300293287280273262
16°F365354342336330321312302291

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
99% of years
16°F or colder
88% 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
2,302
Cooling degree days, base 65°F
2,695
Growing degree days, base 40°F
9,594
Growing degree days, base 45°F
7,909
Growing degree days, base 50°F
6,366
Growing degree days, base 55°F
4,987
Growing degree days, base 60°F
3,765

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January612036
February406397
March23927279
April64128517
May7336794
June0525975
July05971,062
August05811,046
September4367813
October71124521
November3319179
December569048

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 26 km from Iraan. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00418252 (Sheffield). Public domain.