Tropic climate

Tropic Frost Dates and Growing Season

NOAA 1991-2020 normals for Bryce Canyon Np Hqrs, 8 km from Tropic, elevation 7890 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bryce Canyon Np Hqrs. 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 125 days.

Median at 36°F
last June 7, first September 18
Median at 32°F
last May 23, first September 27
Median at 28°F
last May 7, first October 8

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

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 8Sep 11Sep 15Sep 18Sep 20Sep 22Sep 25Sep 28
32°FSep 13Sep 19Sep 22Sep 25Sep 27Sep 29Oct 1Oct 5Oct 11
28°FSep 25Sep 28Oct 1Oct 5Oct 8Oct 12Oct 15Oct 19Oct 24
24°FOct 5Oct 11Oct 16Oct 19Oct 22Oct 26Oct 29Nov 1Nov 6
20°FOct 17Oct 23Oct 27Oct 31Nov 2Nov 5Nov 8Nov 12Nov 16
16°FOct 27Nov 1Nov 5Nov 9Nov 12Nov 15Nov 18Nov 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°F11811210810410096928780
32°F145138133129125121117111103
28°F174167162157153149143138132
24°F200193187182177173167161154
20°F229221214209204199193186177
16°F255248242236231225219212203

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
7,610
Cooling degree days, base 65°F
128
Growing degree days, base 40°F
3,304
Growing degree days, base 45°F
2,346
Growing degree days, base 50°F
1,554
Growing degree days, base 55°F
918
Growing degree days, base 60°F
432

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,18000
February1,01900
March94400
April714010
May470188
June17622305
July3871498
August7233426
September2772198
October618029
November92101
December1,18100

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 8 km from Tropic. 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 USC00421008 (Bryce Canyon Np Hqrs). Public domain.