Thoreau climate

Thoreau Frost Dates and Growing Season

NOAA 1991-2020 normals for Thoreau 12 Se, 13.4 km from Thoreau, elevation 7425 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Thoreau 12 Se. 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 29 and the first fall freeze around September 26, a growing season of about 118 days.

Median at 36°F
last June 6, first September 17
Median at 32°F
last May 29, first September 26
Median at 28°F
last May 15, 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 21Jun 16Jun 12Jun 8Jun 6Jun 3Jun 1May 30May 25
32°FJun 12Jun 6Jun 3May 31May 29May 24May 21May 17May 11
28°FJun 2May 26May 22May 19May 15May 11May 7May 3Apr 28
24°FMay 20May 14May 9May 5May 2Apr 29Apr 25Apr 21Apr 14
20°FMay 9May 2Apr 27Apr 22Apr 18Apr 14Apr 10Apr 6Apr 1
16°FApr 29Apr 17Apr 10Apr 5Apr 1Mar 28Mar 23Mar 19Mar 13

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 6Sep 10Sep 13Sep 15Sep 17Sep 19Sep 22Sep 25Sep 29
32°FSep 13Sep 16Sep 20Sep 23Sep 26Sep 28Oct 1Oct 3Oct 6
28°FSep 21Sep 26Sep 30Oct 1Oct 3Oct 5Oct 8Oct 11Oct 15
24°FOct 1Oct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 20Oct 25
20°FOct 7Oct 12Oct 15Oct 18Oct 20Oct 23Oct 27Oct 30Nov 4
16°FOct 15Oct 20Oct 23Oct 26Oct 30Nov 2Nov 5Nov 10Nov 16

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°F11711210810410198948882
32°F13913212712111811411110698
28°F161154149144139135130124117
24°F184177171167163157153147140
20°F207200195190185180175169161
16°F235227221216210205200192183

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
5,990
Cooling degree days, base 65°F
424
Growing degree days, base 40°F
4,606
Growing degree days, base 45°F
3,426
Growing degree days, base 50°F
2,435
Growing degree days, base 55°F
1,608
Growing degree days, base 60°F
936

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,08800
February84701
March74607
April508163
May2768222
June50106506
July4173634
August13108560
September13827344
October466191
November77708
December1,07600

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 13.4 km from Thoreau. 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 USC00298834 (Thoreau 12 Se). Public domain.