Marengo climate

Marengo Frost Dates and Growing Season

NOAA 1991-2020 normals for Williamsburg 1E, 16 km from Marengo, elevation 780 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Williamsburg 1E. 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 28 and the first fall freeze around October 9, a growing season of about 164 days.

Median at 36°F
last May 7, first September 30
Median at 32°F
last April 28, first October 9
Median at 28°F
last April 18, first October 19

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 21May 16May 12May 9May 7May 4May 2Apr 29Apr 24
32°FMay 12May 7May 3May 1Apr 28Apr 25Apr 22Apr 18Apr 14
28°FMay 2Apr 28Apr 24Apr 21Apr 18Apr 15Apr 12Apr 8Apr 4
24°FApr 24Apr 18Apr 13Apr 10Apr 7Apr 4Apr 1Mar 29Mar 23
20°FApr 13Apr 7Apr 3Mar 31Mar 29Mar 25Mar 21Mar 17Mar 10
16°FApr 2Mar 29Mar 25Mar 21Mar 18Mar 14Mar 11Mar 7Mar 2

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 17Sep 21Sep 24Sep 27Sep 30Oct 2Oct 4Oct 7Oct 11
32°FSep 24Sep 29Oct 2Oct 6Oct 9Oct 11Oct 14Oct 17Oct 21
28°FOct 4Oct 10Oct 14Oct 17Oct 19Oct 21Oct 24Oct 27Oct 31
24°FOct 15Oct 20Oct 23Oct 26Oct 28Oct 30Nov 1Nov 4Nov 10
20°FOct 26Oct 30Nov 1Nov 4Nov 6Nov 10Nov 13Nov 17Nov 23
16°FNov 2Nov 7Nov 11Nov 13Nov 17Nov 20Nov 24Nov 28Dec 4

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°F162157152148145142138133127
32°F181176171167164160156151145
28°F202196191186182178174169161
24°F223215210207203199194188181
20°F246239233228223219214208201
16°F268259255250245241236230222

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
6,866
Cooling degree days, base 65°F
785
Growing degree days, base 40°F
5,058
Growing degree days, base 45°F
3,960
Growing degree days, base 50°F
2,981
Growing degree days, base 55°F
2,123
Growing degree days, base 60°F
1,387

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41300
February1,15801
March895122
April503594
May20250329
June29178598
July5262722
August15198648
September12681411
October45111137
November837018
December1,23201

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 16 km from Marengo. 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 USC00139067 (Williamsburg 1E). Public domain.