Callahan climate

Callahan Frost Dates and Growing Season

NOAA 1991-2020 normals for Jacksonville, 15.1 km from Callahan, elevation 33 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jacksonville. 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 February 25 and the first fall freeze around December 7, a growing season of about 288 days.

Median at 36°F
last March 13, first November 22
Median at 32°F
last February 25, first December 7
Median at 28°F
last February 4, first January 2

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 1Mar 25Mar 20Mar 16Mar 13Mar 9Mar 5Feb 28Feb 19
32°FMar 19Mar 12Mar 7Mar 2Feb 25Feb 19Feb 13Feb 4Jan 22
28°FMar 4Feb 26Feb 17Feb 10Feb 4Jan 30Jan 22Jan 15Jan 4
24°FFeb 15Feb 8Feb 3Jan 29Jan 21Jan 17Jan 10Jan 4Dec 26
20°FFeb 12Feb 7Feb 4Jan 29Jan 24Jan 18Jan 14Jan 5Dec 27
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°FNov 7Nov 12Nov 16Nov 19Nov 22Nov 26Dec 1Dec 4Dec 13
32°FNov 17Nov 23Nov 29Dec 3Dec 7Dec 12Dec 22Jan 1Jan 10
28°FNov 29Dec 5Dec 13Dec 26Jan 2Jan 7Jan 13Jan 20Feb 3
24°FDec 9Dec 21Dec 31Jan 4Jan 10Jan 15Jan 21Feb 1Feb 8
20°FDec 26Jan 4Jan 14Jan 17Jan 20Jan 26Feb 2Feb 6Feb 11
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°F287276267260256251245239229
32°F326312303295288282274266256
28°F365350338332325316309300288
24°F365365365365365356344334324
20°F365365365365365365365365356
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
87% of years
24°F or colder
48% of years
20°F or colder
12% of years
16°F or colder
0% 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
1,228
Cooling degree days, base 65°F
2,803
Growing degree days, base 40°F
10,712
Growing degree days, base 45°F
8,923
Growing degree days, base 50°F
7,193
Growing degree days, base 55°F
5,574
Growing degree days, base 60°F
4,101

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January35015193
February23424235
March14364394
April43136543
May4311772
June0459909
July05441,009
August0530995
September0416865
October25217657
November14461375
December28527246

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 15.1 km from Callahan. 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 USW00013889 (Jacksonville). Public domain.