Ridgefield climate

Ridgefield Frost Dates and Growing Season

NOAA 1991-2020 normals for Danbury Muni AP, 10 km from Ridgefield, elevation 457 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Danbury Muni AP. 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 May 1 and the first fall freeze around October 14, a growing season of about 166 days.

Median at 36°F
last May 12, first October 2
Median at 32°F
last May 1, first October 14
Median at 28°F
last April 18, first October 27

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 27May 22May 19May 16May 12May 9May 6May 3Apr 30
32°FMay 16May 10May 6May 3May 1Apr 29Apr 26Apr 22Apr 18
28°FMay 4Apr 28Apr 24Apr 21Apr 18Apr 15Apr 11Apr 7Apr 3
24°FApr 19Apr 14Apr 9Apr 5Apr 3Apr 1Mar 30Mar 26Mar 21
20°FApr 5Apr 1Mar 29Mar 26Mar 22Mar 20Mar 17Mar 13Mar 7
16°FMar 28Mar 22Mar 19Mar 16Mar 13Mar 10Mar 6Mar 2Feb 25

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 21Sep 25Sep 29Oct 1Oct 2Oct 5Oct 7Oct 11Oct 16
32°FOct 1Oct 4Oct 7Oct 11Oct 14Oct 17Oct 20Oct 24Oct 29
28°FOct 11Oct 16Oct 20Oct 23Oct 27Oct 30Nov 1Nov 4Nov 8
24°FOct 24Oct 29Nov 1Nov 4Nov 6Nov 10Nov 13Nov 17Nov 23
20°FNov 5Nov 10Nov 13Nov 16Nov 19Nov 22Nov 27Dec 1Dec 5
16°FNov 16Nov 21Nov 26Nov 29Dec 1Dec 4Dec 8Dec 13Dec 23

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°F162156151147143139135131126
32°F187180175170166162157153146
28°F211204199195191186182176168
24°F237230225220216212207203195
20°F263256250246242237232228221
16°F287279273269264260255249243

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
6,158
Cooling degree days, base 65°F
594
Growing degree days, base 40°F
4,832
Growing degree days, base 45°F
3,681
Growing degree days, base 50°F
2,690
Growing degree days, base 55°F
1,843
Growing degree days, base 60°F
1,140

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,17801
February1,00201
March870010
April523368
May24622254
June51108507
July6223682
August13175626
September12058391
October4236127
November714020
December1,01203

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 10 km from Ridgefield. 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 USW00054734 (Danbury Muni AP). Public domain.