Belfast climate

Belfast Frost Dates and Growing Season

NOAA 1991-2020 normals for Phillipsburg-Easton Brg, 11.5 km from Belfast, elevation 232 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Phillipsburg-Easton Brg. 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 18 and the first fall freeze around October 25, a growing season of about 188 days.

Median at 36°F
last May 1, first October 13
Median at 32°F
last April 18, first October 25
Median at 28°F
last April 4, first November 4

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 17May 11May 7May 4May 1Apr 28Apr 25Apr 22Apr 17
32°FMay 5Apr 29Apr 24Apr 21Apr 18Apr 15Apr 12Apr 8Apr 5
28°FApr 18Apr 12Apr 9Apr 6Apr 4Apr 2Mar 31Mar 29Mar 23
24°FApr 6Apr 2Mar 31Mar 29Mar 25Mar 22Mar 19Mar 16Mar 10
20°FMar 29Mar 24Mar 21Mar 18Mar 16Mar 13Mar 9Mar 6Mar 1
16°FMar 21Mar 17Mar 13Mar 9Mar 6Mar 3Feb 28Feb 24Feb 16

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°FOct 1Oct 4Oct 7Oct 10Oct 13Oct 17Oct 20Oct 23Oct 27
32°FOct 11Oct 16Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5
28°FOct 24Oct 28Oct 31Nov 1Nov 4Nov 6Nov 9Nov 12Nov 16
24°FNov 2Nov 6Nov 9Nov 11Nov 13Nov 16Nov 18Nov 22Nov 28
20°FNov 9Nov 13Nov 17Nov 20Nov 23Nov 27Nov 30Dec 5Dec 13
16°FNov 17Nov 23Nov 28Dec 1Dec 7Dec 13Dec 18Dec 24Jan 1

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°F184177172168164160155150143
32°F206201197192188184179173165
28°F230224219216212209206202195
24°F254248242238234230226221216
20°F278269263259254249245239233
16°F302294288283276271266259251

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
5,516
Cooling degree days, base 65°F
848
Growing degree days, base 40°F
5,465
Growing degree days, base 45°F
4,259
Growing degree days, base 50°F
3,197
Growing degree days, base 55°F
2,270
Growing degree days, base 60°F
1,488

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09700
February94502
March805021
April4305115
May17438336
June22170598
July1299764
August4228690
September7898469
October3459173
November662027
December95503

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 11.5 km from Belfast. 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 USC00286979 (Phillipsburg-Easton Brg). Public domain.