Saint Johns climate

Saint Johns Frost Dates and Growing Season

NOAA 1991-2020 normals for Saint Johns, 4 km from Saint Johns, elevation 5790 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Saint Johns. 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 2 and the first fall freeze around October 14, a growing season of about 164 days.

Median at 36°F
last May 14, first October 6
Median at 32°F
last May 2, first October 14
Median at 28°F
last April 19, first October 23

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°FMay 30May 24May 20May 17May 14May 11May 8May 4Apr 30
32°FMay 17May 12May 7May 5May 2Apr 30Apr 26Apr 23Apr 18
28°FMay 5Apr 30Apr 26Apr 22Apr 19Apr 16Apr 13Apr 8Apr 4
24°FApr 23Apr 16Apr 11Apr 6Apr 3Mar 31Mar 28Mar 24Mar 18
20°FApr 7Apr 1Mar 27Mar 23Mar 19Mar 16Mar 12Mar 8Feb 28
16°FMar 20Mar 14Mar 10Mar 6Mar 2Feb 27Feb 22Feb 17Feb 9

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 24Sep 28Oct 1Oct 4Oct 6Oct 8Oct 11Oct 14Oct 18
32°FOct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 19Oct 22Oct 27
28°FOct 9Oct 13Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 5
24°FOct 17Oct 23Oct 26Oct 29Nov 1Nov 4Nov 7Nov 12Nov 16
20°FOct 26Nov 1Nov 4Nov 8Nov 12Nov 15Nov 18Nov 21Nov 25
16°FNov 4Nov 11Nov 16Nov 19Nov 22Nov 25Nov 28Dec 1Dec 6

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°F163157152148144140135131123
32°F182176172168164161157153147
28°F205199194189185181176171164
24°F233225220214210205200193185
20°F262255248243237232226220212
16°F291281275269265260254248239

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
4,638
Cooling degree days, base 65°F
890
Growing degree days, base 40°F
5,901
Growing degree days, base 45°F
4,558
Growing degree days, base 50°F
3,399
Growing degree days, base 55°F
2,405
Growing degree days, base 60°F
1,569

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January92700
February70404
March581032
April3602138
May13236373
June11197636
July0319784
August1243707
September3791504
October3023196
November639024
December94401

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 km from Saint Johns. 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 USC00027435 (Saint Johns). Public domain.