Millard County climate

Millard County Frost Dates and Growing Season

NOAA 1991-2020 normals for Black Rock, 42.7 km from Millard County, elevation 4916 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Black Rock. 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 23 and the first fall freeze around September 27, a growing season of about 124 days.

Median at 36°F
last June 7, first September 17
Median at 32°F
last May 23, first September 27
Median at 28°F
last May 7, first October 5

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 25Jun 19Jun 14Jun 10Jun 7Jun 4Jun 1May 28May 22
32°FJun 11Jun 5Jun 1May 28May 23May 19May 15May 10May 5
28°FMay 27May 19May 14May 10May 7May 4May 1Apr 28Apr 22
24°FMay 10May 5May 1Apr 27Apr 24Apr 21Apr 17Apr 13Apr 8
20°FApr 27Apr 21Apr 17Apr 13Apr 9Apr 6Apr 2Mar 30Mar 24
16°FApr 14Apr 6Apr 2Mar 29Mar 25Mar 20Mar 13Mar 7Feb 28

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 3Sep 7Sep 11Sep 14Sep 17Sep 20Sep 23Sep 26Sep 30
32°FSep 14Sep 19Sep 22Sep 24Sep 27Sep 30Oct 1Oct 4Oct 9
28°FSep 23Sep 27Sep 30Oct 2Oct 5Oct 8Oct 11Oct 16Oct 21
24°FOct 1Oct 5Oct 9Oct 13Oct 17Oct 19Oct 23Oct 26Oct 31
20°FOct 10Oct 15Oct 19Oct 23Oct 26Oct 29Nov 1Nov 4Nov 8
16°FOct 18Oct 25Oct 29Nov 1Nov 4Nov 6Nov 10Nov 13Nov 19

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°F1201131081049995908678
32°F148140134128124120115109100
28°F169163158154150145140135126
24°F195189182178174169165159152
20°F222214208203198193188182175
16°F250242236230224219214208200

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
5,846
Cooling degree days, base 65°F
760
Growing degree days, base 40°F
5,127
Growing degree days, base 45°F
3,919
Growing degree days, base 50°F
2,891
Growing degree days, base 55°F
2,029
Growing degree days, base 60°F
1,323

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10700
February84102
March662022
April464181
May23516261
June55127523
July2314776
August5248708
September11054399
October4461108
November797011
December1,12400

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 42.7 km from Millard County. 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 USC00420730 (Black Rock). Public domain.