San Juan County climate

San Juan County Frost Dates and Growing Season

NOAA 1991-2020 normals for Natural Bridges Nm, 15.3 km from San Juan County, elevation 6508 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Natural Bridges Nm. 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 5 and the first fall freeze around October 13, a growing season of about 157 days.

Median at 36°F
last May 20, first October 5
Median at 32°F
last May 5, first October 13
Median at 28°F
last April 24, 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°FJun 6Jun 1May 28May 24May 20May 17May 12May 8May 3
32°FMay 27May 19May 13May 9May 5May 2Apr 30Apr 26Apr 22
28°FMay 11May 5Apr 30Apr 28Apr 24Apr 21Apr 18Apr 13Apr 6
24°FApr 27Apr 21Apr 17Apr 12Apr 9Apr 5Apr 1Mar 24Mar 16
20°FApr 13Apr 6Apr 1Mar 25Mar 17Mar 11Mar 7Mar 2Feb 24
16°FMar 27Mar 14Mar 7Mar 3Feb 27Feb 23Feb 19Feb 13Feb 5

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 23Sep 26Sep 29Oct 2Oct 5Oct 7Oct 11Oct 13Oct 17
32°FSep 29Oct 2Oct 6Oct 9Oct 13Oct 16Oct 19Oct 22Oct 27
28°FOct 7Oct 12Oct 15Oct 19Oct 23Oct 26Oct 29Nov 2Nov 8
24°FOct 16Oct 22Oct 27Oct 30Nov 3Nov 6Nov 10Nov 14Nov 20
20°FOct 26Nov 2Nov 7Nov 12Nov 16Nov 19Nov 22Nov 25Dec 1
16°FNov 6Nov 14Nov 19Nov 22Nov 25Nov 29Dec 2Dec 7Dec 13

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°F155148143138134130125120112
32°F177170166161157152147142133
28°F203195190186181175171165157
24°F234226218212208202197190181
20°F267257250244237231224218208
16°F297288282275269263257249238

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
5,925
Cooling degree days, base 65°F
751
Growing degree days, base 40°F
5,027
Growing degree days, base 45°F
3,878
Growing degree days, base 50°F
2,891
Growing degree days, base 55°F
2,047
Growing degree days, base 60°F
1,333

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09900
February88300
March733012
April518066
May25522266
June44148555
July2292755
August8221677
September9467428
October4312122
November765010
December1,09300

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 15.3 km from San Juan County. 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 USC00426053 (Natural Bridges Nm). Public domain.