Glen Ullin climate

Glen Ullin Frost Dates and Growing Season

NOAA 1991-2020 normals for Hebron, 18.9 km from Glen Ullin, elevation 2160 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hebron. 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 19 and the first fall freeze around September 21, a growing season of about 123 days.

Median at 36°F
last May 31, first September 10
Median at 32°F
last May 19, first September 21
Median at 28°F
last May 10, first September 30

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 14Jun 8Jun 4Jun 2May 31May 28May 25May 22May 17
32°FJun 2May 28May 25May 21May 19May 16May 14May 11May 7
28°FMay 23May 18May 15May 13May 10May 8May 5May 3Apr 30
24°FMay 15May 11May 7May 4May 2Apr 30Apr 27Apr 22Apr 17
20°FMay 5May 1Apr 28Apr 25Apr 21Apr 18Apr 16Apr 12Apr 9
16°FApr 28Apr 22Apr 18Apr 15Apr 13Apr 11Apr 8Apr 5Apr 1

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°FAug 25Sep 1Sep 4Sep 7Sep 10Sep 12Sep 16Sep 20Sep 24
32°FSep 7Sep 11Sep 15Sep 19Sep 21Sep 24Sep 27Sep 30Oct 4
28°FSep 15Sep 21Sep 25Sep 28Sep 30Oct 3Oct 6Oct 9Oct 14
24°FSep 24Sep 30Oct 3Oct 6Oct 9Oct 12Oct 15Oct 18Oct 22
20°FOct 3Oct 7Oct 11Oct 14Oct 17Oct 20Oct 23Oct 27Oct 31
16°FOct 10Oct 15Oct 20Oct 22Oct 26Oct 29Nov 1Nov 5Nov 11

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°F12011410910410097938880
32°F141135130127123120116111104
28°F160154149145141138134129122
24°F178172167163160156152147140
20°F197191186182178173168164157
16°F216209204199195192187182175

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
8,892
Cooling degree days, base 65°F
376
Growing degree days, base 40°F
3,728
Growing degree days, base 45°F
2,802
Growing degree days, base 50°F
1,998
Growing degree days, base 55°F
1,322
Growing degree days, base 60°F
774

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,59900
February1,33700
March1,13903
April731128
May38711166
June12552380
July38154581
August59131539
September26127252
October689146
November1,07903
December1,44800

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 18.9 km from Glen Ullin. 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 USC00324102 (Hebron). Public domain.