Clarkson Valley climate

Clarkson Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for St Charles 7 Ssw, 9.4 km from Clarkson Valley, elevation 450 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for St Charles 7 Ssw. 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 4 and the first fall freeze around October 29, a growing season of about 206 days.

Median at 36°F
last April 16, first October 19
Median at 32°F
last April 4, first October 29
Median at 28°F
last March 25, first November 8

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 1Apr 26Apr 22Apr 19Apr 16Apr 13Apr 10Apr 7Apr 3
32°FApr 21Apr 14Apr 10Apr 7Apr 4Apr 2Mar 31Mar 27Mar 20
28°FApr 8Apr 3Mar 31Mar 29Mar 25Mar 22Mar 18Mar 13Mar 8
24°FMar 30Mar 26Mar 21Mar 17Mar 14Mar 11Mar 7Mar 4Feb 27
20°FMar 20Mar 15Mar 12Mar 8Mar 5Mar 2Feb 28Feb 24Feb 16
16°FMar 13Mar 8Mar 5Mar 1Feb 26Feb 23Feb 18Feb 12Feb 4

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°FOct 5Oct 11Oct 14Oct 16Oct 19Oct 21Oct 24Oct 27Oct 31
32°FOct 15Oct 20Oct 24Oct 27Oct 29Oct 31Nov 2Nov 6Nov 11
28°FOct 27Nov 1Nov 2Nov 5Nov 8Nov 11Nov 16Nov 21Nov 27
24°FNov 4Nov 8Nov 12Nov 16Nov 20Nov 24Nov 27Dec 1Dec 7
20°FNov 10Nov 18Nov 23Nov 27Dec 1Dec 4Dec 8Dec 12Dec 20
16°FNov 23Nov 28Dec 2Dec 7Dec 11Dec 16Dec 21Dec 25Jan 1

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°F202197193189185181176172165
32°F228220215210206202198193186
28°F252244239233228224219213207
24°F274266260254249245240234227
20°F295287281275271266260254247
16°F317308302295289285278270259

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
4,676
Cooling degree days, base 65°F
1,528
Growing degree days, base 40°F
6,842
Growing degree days, base 45°F
5,511
Growing degree days, base 50°F
4,318
Growing degree days, base 55°F
3,256
Growing degree days, base 60°F
2,326

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,05206
February828017
March624579
April29032242
May83132515
June8314756
July0434899
August2383846
September45185591
October25840279
November578377
December908013

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 9.4 km from Clarkson Valley. 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 USC00237398 (St Charles 7 Ssw). Public domain.