McLean climate

McLean Frost Dates and Growing Season

NOAA 1991-2020 normals for Mc Lean, 0.8 km from McLean, elevation 2632 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mc Lean. 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 10 and the first fall freeze around October 30, a growing season of about 201 days.

Median at 36°F
last April 22, first October 22
Median at 32°F
last April 10, first October 30
Median at 28°F
last March 30, first November 9

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

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 6Oct 13Oct 17Oct 20Oct 22Oct 25Oct 27Oct 30Nov 3
32°FOct 14Oct 20Oct 23Oct 27Oct 30Nov 2Nov 4Nov 8Nov 13
28°FOct 23Oct 30Nov 3Nov 5Nov 9Nov 12Nov 15Nov 20Nov 25
24°FNov 3Nov 7Nov 11Nov 15Nov 19Nov 23Nov 26Dec 1Dec 6
20°FNov 10Nov 17Nov 23Nov 27Nov 30Dec 4Dec 8Dec 13Dec 21
16°FNov 21Nov 29Dec 4Dec 8Dec 13Dec 18Dec 23Dec 31Jan 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°F205197190186182178173168160
32°F226217210205201197191185176
28°F251242236230224219214208199
24°F277267261255250244238230220
20°F303293284278273267262255245
16°F335322313306300293285277266

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
99% 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
3,504
Cooling degree days, base 65°F
1,667
Growing degree days, base 40°F
7,663
Growing degree days, base 45°F
6,152
Growing degree days, base 50°F
4,793
Growing degree days, base 55°F
3,586
Growing degree days, base 60°F
2,544

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January787019
February616036
March4287150
April20233301
May56136546
June3328775
July0449914
August0425889
September20237667
October16947358
November4604118
December762020

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 0.8 km from McLean. 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 USC00415770 (Mc Lean). Public domain.