Williston climate

Williston Frost Dates and Growing Season

NOAA 1991-2020 normals for Burlington Intl AP, 7.3 km from Williston, elevation 330 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Burlington 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 April 29 and the first fall freeze around October 15, a growing season of about 169 days.

Median at 36°F
last May 8, first October 4
Median at 32°F
last April 29, first October 15
Median at 28°F
last April 18, first October 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°FMay 23May 18May 14May 11May 8May 5May 3Apr 30Apr 27
32°FMay 11May 6May 3May 1Apr 29Apr 26Apr 24Apr 21Apr 17
28°FApr 30Apr 25Apr 22Apr 20Apr 18Apr 15Apr 12Apr 9Apr 5
24°FApr 18Apr 15Apr 12Apr 9Apr 7Apr 4Apr 3Mar 31Mar 27
20°FApr 11Apr 6Apr 3Apr 2Mar 31Mar 29Mar 25Mar 21Mar 17
16°FApr 3Mar 31Mar 29Mar 26Mar 22Mar 20Mar 17Mar 14Mar 9

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 23Sep 27Sep 30Oct 1Oct 4Oct 6Oct 9Oct 13Oct 19
32°FOct 2Oct 6Oct 9Oct 12Oct 15Oct 18Oct 22Oct 26Nov 1
28°FOct 12Oct 17Oct 22Oct 25Oct 28Nov 1Nov 4Nov 7Nov 12
24°FOct 26Oct 31Nov 3Nov 6Nov 9Nov 12Nov 15Nov 19Nov 23
20°FNov 6Nov 10Nov 14Nov 17Nov 20Nov 23Nov 26Nov 30Dec 3
16°FNov 14Nov 20Nov 24Nov 26Nov 30Dec 1Dec 4Dec 7Dec 13

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°F166159155151147144140136129
32°F187181177172169164161156149
28°F211204200196193189185180173
24°F234227222218215211207202196
20°F253247242238234230225221215
16°F270264259254250246242238231

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
6,960
Cooling degree days, base 65°F
656
Growing degree days, base 40°F
4,742
Growing degree days, base 45°F
3,665
Growing degree days, base 50°F
2,724
Growing degree days, base 55°F
1,905
Growing degree days, base 60°F
1,209

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,36701
February1,17900
March1,01607
April586459
May23632278
June50123524
July6235694
August15191642
September13466387
October4595113
November773019
December1,14201

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 7.3 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 USW00014742 (Burlington Intl AP). Public domain.