Rockford climate

Rockford Frost Dates and Growing Season

NOAA 1991-2020 normals for Charles City, 22.5 km from Rockford, elevation 993 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Charles City. 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 30 and the first fall freeze around October 6, a growing season of about 157 days.

Median at 36°F
last May 9, first September 27
Median at 32°F
last April 30, first October 6
Median at 28°F
last April 21, first October 17

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 22May 18May 15May 12May 9May 7May 4May 1Apr 27
32°FMay 14May 10May 6May 3Apr 30Apr 28Apr 24Apr 20Apr 15
28°FMay 6May 1Apr 28Apr 24Apr 21Apr 17Apr 14Apr 10Apr 5
24°FApr 29Apr 22Apr 17Apr 13Apr 9Apr 7Apr 3Mar 31Mar 26
20°FApr 16Apr 10Apr 5Apr 2Mar 31Mar 28Mar 24Mar 20Mar 13
16°FApr 8Apr 2Mar 29Mar 25Mar 21Mar 18Mar 13Mar 10Mar 5

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 15Sep 19Sep 22Sep 25Sep 27Sep 30Oct 3Oct 5Oct 9
32°FSep 21Sep 26Oct 1Oct 3Oct 6Oct 8Oct 11Oct 15Oct 19
28°FOct 3Oct 7Oct 10Oct 14Oct 17Oct 19Oct 22Oct 25Oct 29
24°FOct 12Oct 19Oct 21Oct 24Oct 27Oct 29Oct 31Nov 4Nov 9
20°FOct 24Oct 29Oct 31Nov 2Nov 5Nov 7Nov 10Nov 13Nov 18
16°FNov 2Nov 5Nov 8Nov 11Nov 14Nov 16Nov 20Nov 24Nov 29

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°F159153148145141137133129123
32°F178171166162157154151146140
28°F198192187182178174170164157
24°F218211206202198194190184177
20°F241234227223218214210205196
16°F258251246242238233229223216

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
7,356
Cooling degree days, base 65°F
652
Growing degree days, base 40°F
4,758
Growing degree days, base 45°F
3,700
Growing degree days, base 50°F
2,754
Growing degree days, base 55°F
1,924
Growing degree days, base 60°F
1,218

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50000
February1,23100
March955115
April532482
May22640298
June36147561
July8227683
August20164609
September14464380
October4856114
November900012
December1,31900

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 22.5 km from Rockford. 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 USC00131402 (Charles City). Public domain.