Brantleyville climate

Brantleyville Frost Dates and Growing Season

NOAA 1991-2020 normals for Helena, 7.4 km from Brantleyville, elevation 480 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Helena. 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 19 and the first fall freeze around November 8, a growing season of about 236 days.

Median at 36°F
last April 3, first October 30
Median at 32°F
last March 19, first November 8
Median at 28°F
last March 4, first November 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°FApr 21Apr 16Apr 11Apr 7Apr 3Mar 31Mar 28Mar 22Mar 15
32°FApr 9Apr 2Mar 29Mar 24Mar 19Mar 15Mar 10Mar 4Feb 26
28°FMar 25Mar 17Mar 12Mar 8Mar 4Feb 28Feb 25Feb 21Feb 8
24°FMar 12Mar 4Feb 28Feb 23Feb 17Feb 11Feb 4Jan 30Jan 22
20°FMar 1Feb 20Feb 13Feb 6Feb 1Jan 28Jan 21Jan 14Jan 2
16°FFeb 16Feb 6Feb 1Jan 28Jan 23Jan 18Jan 13Jan 4Dec 26

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 17Oct 21Oct 24Oct 27Oct 30Nov 1Nov 4Nov 8Nov 13
32°FOct 26Oct 31Nov 2Nov 5Nov 8Nov 11Nov 15Nov 20Nov 29
28°FNov 3Nov 7Nov 12Nov 17Nov 22Nov 27Dec 1Dec 5Dec 13
24°FNov 13Nov 21Nov 27Dec 1Dec 5Dec 10Dec 21Jan 1Jan 8
20°FNov 28Dec 5Dec 11Dec 20Dec 27Jan 2Jan 6Jan 14Jan 27
16°FDec 9Dec 21Dec 29Jan 2Jan 8Jan 14Jan 20Jan 29Feb 5

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°F235226219215210206201196189
32°F261252246241236230224217210
28°F292281274268262257251244235
24°F326315306301294287279271261
20°F364350339333327319311303292
16°F365365365365355346337330316

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
90% of years
16°F or colder
61% 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
2,542
Cooling degree days, base 65°F
2,186
Growing degree days, base 40°F
8,903
Growing degree days, base 45°F
7,269
Growing degree days, base 50°F
5,766
Growing degree days, base 55°F
4,406
Growing degree days, base 60°F
3,210

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January630167
February454498
March28522242
April10868413
May20232677
June0410859
July0518983
August0499964
September4328774
October11593448
November36210156
December564385

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 7.4 km from Brantleyville. 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 USC00013781 (Helena). Public domain.