Hamilton climate

Hamilton Frost Dates and Growing Season

NOAA 1991-2020 normals for Hamilton, 0.6 km from Hamilton, elevation 3585 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hamilton. 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 21 and the first fall freeze around September 22, a growing season of about 122 days.

Median at 36°F
last June 10, first September 9
Median at 32°F
last May 21, first September 22
Median at 28°F
last May 5, first October 2

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 28Jun 22Jun 18Jun 13Jun 10Jun 6Jun 3May 31May 25
32°FJun 6Jun 1May 28May 24May 21May 18May 14May 11May 7
28°FMay 19May 14May 10May 8May 5May 3Apr 30Apr 27Apr 20
24°FMay 5May 1Apr 28Apr 24Apr 20Apr 17Apr 14Apr 9Apr 4
20°FApr 22Apr 14Apr 8Apr 5Apr 2Mar 30Mar 25Mar 19Mar 11
16°FApr 5Mar 30Mar 25Mar 19Mar 14Mar 10Mar 6Mar 2Feb 25

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

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°F11010298938985807466
32°F143136130126122119114107100
28°F167161157153149146141137130
24°F197190185180175171167162155
20°F231223216211206201196190181
16°F261252246240235229223215206

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
7,551
Cooling degree days, base 65°F
216
Growing degree days, base 40°F
3,439
Growing degree days, base 45°F
2,457
Growing degree days, base 50°F
1,654
Growing degree days, base 55°F
1,011
Growing degree days, base 60°F
530

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,17800
February99800
March87603
April648021
May4102122
June20521273
July52110522
August7475467
September2748208
October656035
November96302
December1,21800

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 0.6 km from Hamilton. 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 USC00243885 (Hamilton). Public domain.