Black Eagle climate

Black Eagle Frost Dates and Growing Season

NOAA 1991-2020 normals for Great Falls 16ST, 4.1 km from Black Eagle, elevation 3505 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Great Falls 16ST. 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 6 and the first fall freeze around October 1, a growing season of about 147 days.

Median at 36°F
last May 19, first September 21
Median at 32°F
last May 6, first October 1
Median at 28°F
last April 24, first October 11

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 24May 21May 19May 16May 14May 11May 6
32°FMay 19May 14May 11May 8May 6May 3May 1Apr 28Apr 23
28°FMay 8May 3Apr 30Apr 27Apr 24Apr 21Apr 17Apr 13Apr 7
24°FApr 30Apr 25Apr 21Apr 16Apr 13Apr 9Apr 6Apr 2Mar 28
20°FApr 21Apr 14Apr 10Apr 7Apr 3Apr 1Mar 28Mar 21Mar 15
16°FApr 11Apr 6Apr 2Mar 30Mar 25Mar 20Mar 15Mar 10Mar 4

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 14Sep 18Sep 21Sep 23Sep 25Sep 29Oct 3
32°FSep 17Sep 22Sep 25Sep 28Oct 1Oct 4Oct 7Oct 11Oct 16
28°FSep 25Oct 1Oct 4Oct 7Oct 11Oct 15Oct 19Oct 23Oct 29
24°FOct 2Oct 8Oct 15Oct 20Oct 24Oct 27Oct 30Nov 2Nov 8
20°FOct 8Oct 19Oct 26Oct 29Nov 1Nov 3Nov 7Nov 12Nov 19
16°FOct 23Oct 29Nov 1Nov 5Nov 8Nov 12Nov 16Nov 21Nov 26

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°F142135131127124120116111105
32°F166159155151147143140135129
28°F193186180176171165160156149
24°F216207201195191186181175166
20°F236227221215210205199193184
16°F255246239233228222216209200

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
6,942
Cooling degree days, base 65°F
422
Growing degree days, base 40°F
4,278
Growing degree days, base 45°F
3,153
Growing degree days, base 50°F
2,214
Growing degree days, base 55°F
1,457
Growing degree days, base 60°F
857

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,17301
February1,01805
March878012
April578150
May3358181
June12045379
July19186632
August38151578
September22030281
October545381
November881013
December1,13903

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 4.1 km from Black Eagle. 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 USC00243749 (Great Falls 16ST). Public domain.