Greybull climate

Greybull Frost Dates and Growing Season

NOAA 1991-2020 normals for Greybull, 0.2 km from Greybull, elevation 3787 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Greybull. 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 11 and the first fall freeze around September 23, a growing season of about 133 days.

Median at 36°F
last May 23, first September 14
Median at 32°F
last May 11, first September 23
Median at 28°F
last May 2, first October 3

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 6Jun 1May 29May 25May 23May 20May 17May 14May 11
32°FMay 24May 20May 16May 13May 11May 9May 6May 4Apr 30
28°FMay 15May 10May 7May 4May 2Apr 30Apr 27Apr 24Apr 19
24°FMay 6May 1Apr 27Apr 24Apr 21Apr 18Apr 15Apr 11Apr 7
20°FApr 25Apr 19Apr 15Apr 12Apr 8Apr 5Apr 2Mar 31Mar 24
16°FApr 15Apr 8Apr 3Apr 1Mar 29Mar 24Mar 21Mar 16Mar 10

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 2Sep 6Sep 9Sep 12Sep 14Sep 16Sep 19Sep 22Sep 26
32°FSep 11Sep 15Sep 18Sep 21Sep 23Sep 26Sep 29Oct 2Oct 6
28°FSep 21Sep 25Sep 28Oct 1Oct 3Oct 5Oct 9Oct 12Oct 18
24°FSep 29Oct 4Oct 7Oct 11Oct 14Oct 16Oct 20Oct 23Oct 27
20°FOct 8Oct 14Oct 17Oct 21Oct 24Oct 26Oct 29Nov 1Nov 4
16°FOct 16Oct 21Oct 25Oct 29Nov 1Nov 3Nov 5Nov 9Nov 12

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°F13012411911511110810510194
32°F150144140136133130125120115
28°F171166161157153149145141134
24°F195188182179174171166162154
20°F216209204200196192187182175
16°F236229223219215210205200193

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
7,822
Cooling degree days, base 65°F
582
Growing degree days, base 40°F
4,339
Growing degree days, base 45°F
3,315
Growing degree days, base 50°F
2,432
Growing degree days, base 55°F
1,687
Growing degree days, base 60°F
1,071

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,51400
February1,18000
March88107
April569049
May29214222
June7693468
July9254710
August26188628
September19631299
October605148
November1,03401
December1,44000

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 0.2 km from Greybull. 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 USC00484080 (Greybull). Public domain.