Norwalk climate

Norwalk Frost Dates and Growing Season

NOAA 1991-2020 normals for Cashton, 15.9 km from Norwalk, elevation 1370 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cashton. 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 27 and the first fall freeze around October 14, a growing season of about 170 days.

Median at 36°F
last May 7, first October 4
Median at 32°F
last April 27, first October 14
Median at 28°F
last April 17, first October 26

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 10May 7May 4May 2Apr 29Apr 24
32°FMay 11May 6May 3Apr 30Apr 27Apr 24Apr 21Apr 18Apr 14
28°FApr 30Apr 26Apr 23Apr 20Apr 17Apr 14Apr 11Apr 7Apr 3
24°FApr 21Apr 16Apr 12Apr 9Apr 6Apr 4Apr 2Mar 29Mar 23
20°FApr 11Apr 6Apr 3Mar 31Mar 28Mar 24Mar 21Mar 17Mar 12
16°FApr 4Mar 31Mar 27Mar 23Mar 20Mar 17Mar 14Mar 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 22Sep 26Sep 29Oct 2Oct 4Oct 7Oct 9Oct 13Oct 17
32°FOct 1Oct 5Oct 8Oct 12Oct 14Oct 17Oct 21Oct 24Oct 27
28°FOct 11Oct 17Oct 20Oct 24Oct 26Oct 28Oct 31Nov 2Nov 8
24°FOct 23Oct 28Oct 31Nov 2Nov 4Nov 7Nov 10Nov 13Nov 19
20°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 16Nov 19Nov 23Nov 29
16°FNov 6Nov 10Nov 14Nov 17Nov 21Nov 24Nov 26Dec 1Dec 8

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°F167162158154150147144139133
32°F189182178174170166162158152
28°F210205200196192189184179174
24°F231223218215210206203198193
20°F250242238233229225221217209
16°F265259254249245240236231224

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
7,409
Cooling degree days, base 65°F
612
Growing degree days, base 40°F
4,646
Growing degree days, base 45°F
3,606
Growing degree days, base 50°F
2,673
Growing degree days, base 55°F
1,854
Growing degree days, base 60°F
1,162

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,47800
February1,21600
March987011
April556377
May23731278
June47134537
July8214671
August19166612
September14859370
October5045104
November907011
December1,30001

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 15.9 km from Norwalk. 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 USC00471280 (Cashton). Public domain.