Mercer climate

Mercer Frost Dates and Growing Season

NOAA 1991-2020 normals for Rest Lake, 15.1 km from Mercer, elevation 1612 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rest Lake. 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 25 and the first fall freeze around September 21, a growing season of about 117 days.

Median at 32°F
last May 25, first September 21
Median at 28°F
last May 11, first October 1

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°F–––––––––
32°FJun 9Jun 3May 31May 28May 25May 22May 18May 14May 8
28°FMay 28May 22May 18May 14May 11May 7May 3Apr 30Apr 27
24°FMay 17May 10May 5May 2Apr 30Apr 28Apr 25Apr 21Apr 16
20°FMay 4Apr 30Apr 27Apr 23Apr 20Apr 17Apr 14Apr 11Apr 5
16°FApr 26Apr 22Apr 18Apr 15Apr 12Apr 8Apr 5Apr 3Mar 29

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°F–––––––––
32°FSep 3Sep 8Sep 14Sep 18Sep 21Sep 24Sep 28Oct 2Oct 6
28°FSep 14Sep 20Sep 25Sep 29Oct 1Oct 4Oct 6Oct 10Oct 15
24°FSep 25Oct 1Oct 5Oct 9Oct 12Oct 16Oct 20Oct 24Oct 29
20°FOct 7Oct 14Oct 20Oct 24Oct 27Oct 31Nov 2Nov 5Nov 11
16°FOct 23Oct 30Nov 1Nov 3Nov 6Nov 9Nov 12Nov 15Nov 20

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°F116108102969185797058
32°F14113312712111711210610192
28°F163156151147142137132126117
24°F188180174169164159155148140
20°F209203197192188184179173165
16°F227220215211206203198193187

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
9,380
Cooling degree days, base 65°F
262
Growing degree days, base 40°F
3,437
Growing degree days, base 45°F
2,545
Growing degree days, base 50°F
1,769
Growing degree days, base 55°F
1,119
Growing degree days, base 60°F
609

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,69900
February1,42700
March1,23404
April783025
May39214165
June14356369
July6999495
August9567438
September29124224
October681245
November1,07102
December1,49600

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 15.1 km from Mercer. 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 USC00477092 (Rest Lake). Public domain.