Williston climate

Williston Frost Dates and Growing Season

NOAA 1991-2020 normals for Williston Sloulin Intl AP, 3.3 km from Williston, elevation 1902 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Williston Sloulin Intl AP. 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 21 and the first fall freeze around September 21, a growing season of about 123 days.

Median at 36°F
last May 29, first September 12
Median at 32°F
last May 21, first September 21
Median at 28°F
last May 11, first September 28

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°FJun 16Jun 8Jun 4Jun 1May 29May 27May 25May 22May 18
32°FJun 3May 29May 26May 24May 21May 18May 16May 13May 8
28°FMay 25May 20May 16May 14May 11May 8May 5May 3Apr 29
24°FMay 15May 10May 6May 3Apr 30Apr 27Apr 23Apr 19Apr 13
20°FMay 3Apr 29Apr 24Apr 20Apr 17Apr 14Apr 10Apr 7Apr 3
16°FApr 22Apr 17Apr 13Apr 10Apr 6Apr 4Apr 2Mar 30Mar 22

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 1Sep 4Sep 7Sep 10Sep 12Sep 15Sep 17Sep 19Sep 23
32°FSep 9Sep 13Sep 17Sep 19Sep 21Sep 23Sep 25Sep 28Oct 2
28°FSep 16Sep 20Sep 23Sep 25Sep 28Sep 30Oct 3Oct 6Oct 11
24°FSep 23Sep 27Oct 1Oct 4Oct 7Oct 10Oct 13Oct 17Oct 21
20°FOct 1Oct 6Oct 10Oct 13Oct 16Oct 19Oct 22Oct 25Oct 30
16°FOct 9Oct 14Oct 19Oct 22Oct 25Oct 28Oct 31Nov 4Nov 9

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°F122116111108105101969184
32°F140135130127123119115109103
28°F159152147143140136132128120
24°F182173168163159155151145139
20°F202195190185180176170165157
16°F221214209204200195190185176

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
8,906
Cooling degree days, base 65°F
457
Growing degree days, base 40°F
3,912
Growing degree days, base 45°F
2,969
Growing degree days, base 50°F
2,149
Growing degree days, base 55°F
1,450
Growing degree days, base 60°F
882

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,65700
February1,36900
March1,12203
April679032
May35710174
June10862406
July21188632
August41164588
September24031268
October679244
November1,11701
December1,51600

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 3.3 km from Williston. 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 USW00094014 (Williston Sloulin Intl AP). Public domain.