Sullivan climate

Sullivan Frost Dates and Growing Season

NOAA 1991-2020 normals for Keene, 11.8 km from Sullivan, elevation 511 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Keene. 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 14 and the first fall freeze around October 1, a growing season of about 138 days.

Median at 36°F
last May 27, first September 21
Median at 32°F
last May 14, first October 1
Median at 28°F
last May 2, first October 10

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 9Jun 4Jun 1May 30May 27May 24May 21May 17May 13
32°FMay 28May 23May 19May 16May 14May 11May 8May 4Apr 30
28°FMay 16May 11May 8May 5May 2Apr 30Apr 28Apr 25Apr 21
24°FMay 5Apr 30Apr 26Apr 24Apr 21Apr 19Apr 16Apr 11Apr 6
20°FApr 19Apr 15Apr 11Apr 8Apr 6Apr 4Apr 2Mar 31Mar 25
16°FApr 7Apr 4Apr 1Mar 31Mar 29Mar 25Mar 21Mar 18Mar 13

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 7Sep 11Sep 15Sep 18Sep 21Sep 23Sep 27Sep 30Oct 4
32°FSep 18Sep 23Sep 26Sep 29Oct 1Oct 3Oct 5Oct 9Oct 14
28°FSep 29Oct 2Oct 5Oct 7Oct 10Oct 13Oct 17Oct 20Oct 25
24°FOct 7Oct 12Oct 16Oct 20Oct 23Oct 27Oct 31Nov 2Nov 9
20°FOct 19Oct 26Oct 31Nov 2Nov 5Nov 8Nov 12Nov 16Nov 21
16°FNov 4Nov 9Nov 14Nov 17Nov 20Nov 23Nov 27Dec 1Dec 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°F13412812312011711310910498
32°F156150145142138134130125119
28°F180173169164160156153148141
24°F208200195191187183178172165
20°F231225220216212208204199192
16°F257250245240236232228223217

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
7,501
Cooling degree days, base 65°F
375
Growing degree days, base 40°F
4,040
Growing degree days, base 45°F
3,038
Growing degree days, base 50°F
2,165
Growing degree days, base 55°F
1,422
Growing degree days, base 60°F
819

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,38300
February1,18000
March1,04304
April651137
May32913186
June10064415
July22144587
August38114541
September18538313
October537273
November84808
December1,18700

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 11.8 km from Sullivan. 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 USC00274399 (Keene). Public domain.