Guernsey climate

Guernsey Frost Dates and Growing Season

NOAA 1991-2020 normals for Guernsey 2NW, 2.5 km from Guernsey, elevation 4480 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Guernsey 2NW. 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 7 and the first fall freeze around October 6, a growing season of about 152 days.

Median at 36°F
last May 18, first September 28
Median at 32°F
last May 7, first October 6
Median at 28°F
last April 28, first October 16

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 1May 27May 23May 20May 18May 15May 13May 10May 5
32°FMay 21May 16May 13May 10May 7May 4May 1Apr 29Apr 24
28°FMay 10May 5May 2Apr 30Apr 28Apr 24Apr 20Apr 17Apr 13
24°FMay 1Apr 25Apr 21Apr 18Apr 14Apr 11Apr 8Apr 4Mar 30
20°FApr 21Apr 16Apr 11Apr 7Apr 3Mar 31Mar 27Mar 21Mar 14
16°FApr 11Apr 4Mar 31Mar 27Mar 22Mar 18Mar 12Mar 8Mar 3

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 15Sep 20Sep 23Sep 26Sep 28Oct 1Oct 4Oct 6Oct 10
32°FSep 23Sep 28Oct 1Oct 4Oct 6Oct 8Oct 11Oct 14Oct 18
28°FOct 1Oct 6Oct 10Oct 13Oct 16Oct 18Oct 20Oct 22Oct 26
24°FOct 11Oct 16Oct 18Oct 21Oct 23Oct 25Oct 28Oct 30Nov 4
20°FOct 17Oct 22Oct 25Oct 27Oct 30Nov 1Nov 4Nov 8Nov 13
16°FOct 22Oct 27Oct 31Nov 3Nov 7Nov 11Nov 13Nov 18Nov 22

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°F151145141137133130125120113
32°F169163159155152149145140132
28°F189183179175171167163158151
24°F210202197193189186182177169
20°F232223216212207202196192184
16°F252243237231226221216210200

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
6,645
Cooling degree days, base 65°F
725
Growing degree days, base 40°F
4,767
Growing degree days, base 45°F
3,668
Growing degree days, base 50°F
2,732
Growing degree days, base 55°F
1,936
Growing degree days, base 60°F
1,262

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,17700
February1,02503
March831012
April582045
May30918222
June53111508
July3288750
August12244697
September13163391
October507295
November85908
December1,15601

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 2.5 km from Guernsey. 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 USC00484131 (Guernsey 2NW). Public domain.