Riverhead climate

Riverhead Frost Dates and Growing Season

NOAA 1991-2020 normals for Riverhead Rsch Farm, 6.8 km from Riverhead, elevation 100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Riverhead Rsch Farm. 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 6 and the first fall freeze around November 9, a growing season of about 215 days.

Median at 36°F
last April 20, first October 28
Median at 32°F
last April 6, first November 9
Median at 28°F
last March 28, first November 21

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 3Apr 29Apr 25Apr 22Apr 20Apr 17Apr 15Apr 11Apr 7
32°FApr 19Apr 15Apr 12Apr 9Apr 6Apr 4Apr 2Mar 31Mar 27
28°FApr 7Apr 3Apr 1Mar 30Mar 28Mar 24Mar 20Mar 16Mar 12
24°FMar 29Mar 24Mar 20Mar 18Mar 15Mar 13Mar 10Mar 5Feb 28
20°FMar 19Mar 15Mar 12Mar 9Mar 6Mar 3Feb 28Feb 23Feb 14
16°FMar 13Mar 7Mar 2Feb 27Feb 23Feb 17Feb 11Feb 5Jan 30

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 15Oct 19Oct 23Oct 26Oct 28Oct 31Nov 2Nov 5Nov 10
32°FOct 28Nov 1Nov 3Nov 6Nov 9Nov 12Nov 14Nov 18Nov 22
28°FNov 7Nov 12Nov 15Nov 18Nov 21Nov 24Nov 28Dec 1Dec 5
24°FNov 18Nov 24Nov 29Dec 2Dec 4Dec 8Dec 11Dec 17Dec 24
20°FDec 1Dec 7Dec 12Dec 16Dec 20Dec 23Dec 27Jan 1Jan 7
16°FDec 13Dec 22Dec 26Dec 29Jan 1Jan 6Jan 10Jan 16Jan 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°F207202197193190186183177170
32°F233227222218215212208204198
28°F259253247243239236232227220
24°F286278272268263259255249243
20°F309300295290286282276270264
16°F334326318312308303299292285

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
99% 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
4,906
Cooling degree days, base 65°F
945
Growing degree days, base 40°F
5,862
Growing degree days, base 45°F
4,556
Growing degree days, base 50°F
3,416
Growing degree days, base 55°F
2,436
Growing degree days, base 60°F
1,612

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January99703
February86502
March760014
April434397
May16933331
June23161588
July0323787
August1286750
September36125539
October25715240
November540056
December825010

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 6.8 km from Riverhead. 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 USC00307134 (Riverhead Rsch Farm). Public domain.