Mercer County climate

Mercer County Frost Dates and Growing Season

NOAA 1991-2020 normals for Mercer, 8.8 km from Mercer County, elevation 1220 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mercer. 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 15 and the first fall freeze around October 3, a growing season of about 140 days.

Median at 36°F
last May 27, first September 23
Median at 32°F
last May 15, first October 3
Median at 28°F
last May 3, first October 13

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 19Jun 8Jun 3May 31May 27May 24May 20May 16May 10
32°FJun 1May 27May 23May 19May 15May 11May 7May 4Apr 30
28°FMay 21May 15May 10May 6May 3Apr 30Apr 27Apr 24Apr 19
24°FMay 10May 4Apr 30Apr 27Apr 24Apr 21Apr 18Apr 14Apr 8
20°FApr 29Apr 22Apr 19Apr 16Apr 12Apr 8Apr 5Apr 1Mar 28
16°FApr 16Apr 11Apr 7Apr 3Apr 1Mar 29Mar 26Mar 21Mar 15

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 4Sep 11Sep 16Sep 20Sep 23Sep 26Sep 29Oct 2Oct 6
32°FSep 19Sep 24Sep 28Oct 1Oct 3Oct 5Oct 8Oct 12Oct 19
28°FSep 29Oct 3Oct 6Oct 10Oct 13Oct 17Oct 22Oct 26Nov 1
24°FOct 8Oct 13Oct 19Oct 24Oct 29Nov 1Nov 3Nov 6Nov 12
20°FOct 22Oct 29Nov 1Nov 4Nov 7Nov 10Nov 14Nov 19Nov 24
16°FNov 3Nov 7Nov 12Nov 16Nov 20Nov 24Nov 29Dec 3Dec 10

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°F14013312712311811310710086
32°F163155150145140136131125117
28°F185178173168163158153149140
24°F209200195190186181175169160
20°F231223218213209204200194185
16°F259249243238232228223216209

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
6,444
Cooling degree days, base 65°F
465
Growing degree days, base 40°F
4,642
Growing degree days, base 45°F
3,512
Growing degree days, base 50°F
2,525
Growing degree days, base 55°F
1,676
Growing degree days, base 60°F
977

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,22401
February1,03902
March882020
April519387
May25827259
June6795479
July23151594
August25139580
September13946362
October4465118
November757022
December1,06603

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 8.8 km from Mercer County. 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 USC00365651 (Mercer). Public domain.