Lockport climate

Lockport Frost Dates and Growing Season

NOAA 1991-2020 normals for Romeoville WFO, 2.7 km from Lockport, elevation 660 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Romeoville WFO. 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 20 and the first fall freeze around October 22, a growing season of about 184 days.

Median at 36°F
last May 1, first October 12
Median at 32°F
last April 20, first October 22
Median at 28°F
last April 8, first November 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°FMay 17May 13May 8May 4May 1Apr 29Apr 25Apr 21Apr 17
32°FMay 6May 1Apr 27Apr 23Apr 20Apr 17Apr 14Apr 11Apr 7
28°FApr 23Apr 18Apr 14Apr 11Apr 8Apr 6Apr 4Apr 1Mar 27
24°FApr 12Apr 7Apr 3Apr 1Mar 30Mar 26Mar 22Mar 18Mar 13
20°FApr 1Mar 28Mar 25Mar 21Mar 17Mar 14Mar 11Mar 8Mar 2
16°FMar 25Mar 19Mar 15Mar 12Mar 9Mar 5Mar 2Feb 28Feb 21

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 28Oct 2Oct 6Oct 9Oct 12Oct 14Oct 17Oct 20Oct 24
32°FOct 7Oct 14Oct 17Oct 20Oct 22Oct 25Oct 27Oct 30Nov 3
28°FOct 19Oct 24Oct 27Oct 30Nov 1Nov 3Nov 6Nov 11Nov 15
24°FNov 1Nov 4Nov 6Nov 9Nov 12Nov 15Nov 19Nov 22Nov 26
20°FNov 7Nov 11Nov 15Nov 18Nov 21Nov 24Nov 27Dec 1Dec 5
16°FNov 12Nov 18Nov 22Nov 26Nov 29Dec 2Dec 6Dec 11Dec 17

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°F180173169165162158154149142
32°F202196191187184180175170162
28°F226218213209206202198193186
24°F252244239234230226221217211
20°F271263258253249245240235228
16°F290281275270266262258252245

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
6,063
Cooling degree days, base 65°F
947
Growing degree days, base 40°F
5,512
Growing degree days, base 45°F
4,343
Growing degree days, base 50°F
3,305
Growing degree days, base 55°F
2,391
Growing degree days, base 60°F
1,603

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,27401
February1,03603
March806333
April4487119
May18067362
June23200627
July2300763
August5248708
September80106479
October36817181
November738028
December1,10403

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 2.7 km from Lockport. 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 USC00117457 (Romeoville WFO). Public domain.