Merton climate

Merton Frost Dates and Growing Season

NOAA 1991-2020 normals for Richfield 3 Ssw, 10.7 km from Merton, elevation 984 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Richfield 3 Ssw. 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 30 and the first fall freeze around October 16, a growing season of about 167 days.

Median at 36°F
last May 12, first October 4
Median at 32°F
last April 30, first October 16
Median at 28°F
last April 19, first October 27

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

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°F164158153149145141137132125
32°F187180175171167163159154147
28°F209203198194190185181176169
24°F233226221217213210205200191
20°F253246241236233229225220213
16°F271264260254250245241236230

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
7,284
Cooling degree days, base 65°F
580
Growing degree days, base 40°F
4,547
Growing degree days, base 45°F
3,498
Growing degree days, base 50°F
2,585
Growing degree days, base 55°F
1,790
Growing degree days, base 60°F
1,112

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,42100
February1,18600
March981217
April610147
May28224243
June56101496
July11220674
August19172618
September14756365
October4744111
November861015
December1,23700

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 10.7 km from Merton. 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 USC00477148 (Richfield 3 Ssw). Public domain.