Amherst climate

Amherst Frost Dates and Growing Season

NOAA 1991-2020 normals for Littlefield, 21.3 km from Amherst, elevation 3466 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Littlefield. 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 April 14 and the first fall freeze around October 26, a growing season of about 192 days.

Median at 36°F
last April 25, first October 17
Median at 32°F
last April 14, first October 26
Median at 28°F
last April 3, first November 4

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 6May 2Apr 30Apr 28Apr 25Apr 23Apr 20Apr 17Apr 12
32°FApr 28Apr 24Apr 21Apr 18Apr 14Apr 11Apr 8Apr 4Mar 30
28°FApr 21Apr 15Apr 10Apr 6Apr 3Mar 31Mar 28Mar 23Mar 17
24°FApr 8Apr 2Mar 30Mar 25Mar 21Mar 17Mar 13Mar 8Mar 3
20°FMar 27Mar 20Mar 15Mar 11Mar 7Mar 3Feb 28Feb 23Feb 16
16°FMar 14Mar 6Mar 2Feb 26Feb 21Feb 16Feb 9Feb 3Jan 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°FOct 4Oct 8Oct 12Oct 15Oct 17Oct 19Oct 21Oct 24Oct 30
32°FOct 15Oct 18Oct 21Oct 24Oct 26Oct 28Oct 31Nov 2Nov 6
28°FOct 22Oct 27Oct 30Nov 1Nov 4Nov 6Nov 9Nov 12Nov 17
24°FOct 31Nov 4Nov 7Nov 10Nov 13Nov 16Nov 19Nov 23Nov 27
20°FNov 7Nov 12Nov 17Nov 20Nov 23Nov 26Nov 29Dec 3Dec 9
16°FNov 16Nov 24Nov 28Dec 1Dec 5Dec 10Dec 14Dec 21Jan 1

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°F190184180176173169166162157
32°F212205201197192189185180174
28°F236230224218214209205200193
24°F261253248242237232226220212
20°F287278272266262257251245235
16°F324313304296289282275267258

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
3,838
Cooling degree days, base 65°F
1,493
Growing degree days, base 40°F
7,197
Growing degree days, base 45°F
5,732
Growing degree days, base 50°F
4,429
Growing degree days, base 55°F
3,292
Growing degree days, base 60°F
2,315

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January825010
February641026
March4773109
April24322262
May70143541
June3334781
July0417882
August1370834
September34173591
October21629306
November532176
December797013

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 21.3 km from Amherst. 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 USC00415265 (Littlefield). Public domain.