Lyndon climate

Lyndon Frost Dates and Growing Season

NOAA 1991-2020 normals for Saint Johnsbury, 10.5 km from Lyndon, elevation 700 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Saint Johnsbury. 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 13 and the first fall freeze around October 3, a growing season of about 143 days.

Median at 36°F
last May 25, first September 24
Median at 32°F
last May 13, first October 3
Median at 28°F
last May 1, first October 13

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 5Jun 1May 29May 27May 25May 22May 19May 15May 11
32°FMay 25May 21May 19May 16May 13May 10May 8May 4Apr 30
28°FMay 15May 11May 7May 4May 1Apr 30Apr 27Apr 24Apr 20
24°FMay 1Apr 27Apr 24Apr 21Apr 19Apr 17Apr 14Apr 11Apr 7
20°FApr 20Apr 16Apr 13Apr 10Apr 8Apr 6Apr 3Apr 1Mar 29
16°FApr 12Apr 8Apr 5Apr 3Apr 2Mar 31Mar 28Mar 24Mar 19

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 11Sep 15Sep 19Sep 22Sep 24Sep 26Sep 28Oct 1Oct 4
32°FSep 21Sep 26Sep 29Oct 1Oct 3Oct 5Oct 8Oct 11Oct 16
28°FOct 1Oct 4Oct 7Oct 10Oct 13Oct 16Oct 20Oct 24Oct 29
24°FOct 11Oct 16Oct 20Oct 24Oct 27Oct 30Nov 1Nov 4Nov 9
20°FOct 24Oct 30Nov 1Nov 3Nov 5Nov 8Nov 12Nov 15Nov 20
16°FNov 3Nov 7Nov 11Nov 14Nov 16Nov 19Nov 22Nov 26Nov 30

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°F139132129124121118114110105
32°F160153150146143140136132126
28°F183176171168164161157153146
24°F206201196193188185181177172
20°F228221217213210207203198193
16°F247241236232228224221217211

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
7,488
Cooling degree days, base 65°F
432
Growing degree days, base 40°F
4,264
Growing degree days, base 45°F
3,240
Growing degree days, base 50°F
2,343
Growing degree days, base 55°F
1,563
Growing degree days, base 60°F
915

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,43500
February1,22100
March1,05204
April621247
May27619234
June7185464
July14160611
August30123558
September17042331
October512286
November851010
December1,23500

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 10.5 km from Lyndon. 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 USC00437054 (Saint Johnsbury). Public domain.