Iva climate

Iva Frost Dates and Growing Season

NOAA 1991-2020 normals for Hartwell Dam, 16.2 km from Iva, elevation 690 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hartwell Dam. 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 25 and the first fall freeze around November 12, a growing season of about 235 days.

Median at 36°F
last April 7, first November 1
Median at 32°F
last March 25, first November 12
Median at 28°F
last March 11, first November 25

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 21Apr 17Apr 13Apr 10Apr 7Apr 4Apr 1Mar 28Mar 20
32°FApr 10Apr 5Apr 1Mar 28Mar 25Mar 21Mar 17Mar 13Mar 6
28°FMar 29Mar 23Mar 19Mar 15Mar 11Mar 6Mar 1Feb 23Feb 13
24°FMar 17Mar 10Mar 4Feb 27Feb 20Feb 13Feb 5Jan 30Jan 20
20°FMar 6Feb 26Feb 13Feb 6Jan 31Jan 26Jan 20Jan 13Jan 4
16°FFeb 21Feb 7Feb 1Jan 28Jan 22Jan 17Jan 12Jan 5Dec 27

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 19Oct 23Oct 27Oct 29Nov 1Nov 2Nov 5Nov 9Nov 13
32°FOct 30Nov 2Nov 5Nov 9Nov 12Nov 15Nov 18Nov 23Dec 1
28°FNov 8Nov 13Nov 17Nov 21Nov 25Dec 1Dec 4Dec 9Dec 20
24°FNov 20Nov 30Dec 4Dec 9Dec 14Dec 21Dec 27Jan 2Jan 11
20°FDec 7Dec 14Dec 22Dec 28Jan 1Jan 7Jan 13Jan 19Feb 1
16°FDec 17Dec 26Jan 1Jan 5Jan 10Jan 16Jan 19Jan 27Feb 6

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°F233224218213209205201196189
32°F259251245240235229224219212
28°F297286278271265259253247237
24°F335324314306299292286276266
20°F365354344337331325316306295
16°F365365365365360350341333319

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
99% of years
20°F or colder
90% of years
16°F or colder
58% 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
2,959
Cooling degree days, base 65°F
1,805
Growing degree days, base 40°F
8,122
Growing degree days, base 45°F
6,516
Growing degree days, base 50°F
5,075
Growing degree days, base 55°F
3,806
Growing degree days, base 60°F
2,720

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January691033
February538052
March4008150
April16337332
May33169601
June0363813
July0485950
August0432897
September8256699
October13252388
November3933116
December603044

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 16.2 km from Iva. 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 USC00094138 (Hartwell Dam). Public domain.