Warren County climate

Warren County Frost Dates and Growing Season

NOAA 1991-2020 normals for Warrenton, 5.1 km from Warren County, elevation 490 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Warrenton. 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 March 29 and the first fall freeze around November 7, a growing season of about 225 days.

Median at 36°F
last April 8, first October 29
Median at 32°F
last March 29, first November 7
Median at 28°F
last March 13, first November 22

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°FApr 24Apr 19Apr 15Apr 12Apr 8Apr 5Apr 2Mar 30Mar 23
32°FApr 14Apr 8Apr 5Apr 1Mar 29Mar 25Mar 20Mar 15Mar 8
28°FApr 2Mar 27Mar 21Mar 17Mar 13Mar 7Mar 3Feb 25Feb 15
24°FMar 18Mar 12Mar 6Feb 28Feb 24Feb 18Feb 12Feb 5Jan 28
20°FMar 6Feb 27Feb 17Feb 9Feb 4Jan 31Jan 25Jan 17Jan 5
16°FFeb 21Feb 7Feb 2Jan 29Jan 24Jan 18Jan 13Jan 5Dec 29

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 17Oct 21Oct 24Oct 26Oct 29Nov 1Nov 2Nov 6Nov 11
32°FOct 25Oct 31Nov 2Nov 5Nov 7Nov 10Nov 15Nov 19Nov 26
28°FNov 5Nov 9Nov 13Nov 18Nov 22Nov 26Dec 1Dec 5Dec 15
24°FNov 17Nov 23Nov 30Dec 3Dec 8Dec 16Dec 26Jan 1Jan 10
20°FDec 1Dec 8Dec 18Dec 26Jan 1Jan 4Jan 10Jan 18Feb 1
16°FDec 13Dec 24Dec 31Jan 4Jan 8Jan 14Jan 20Jan 27Feb 6

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°F224217211206203199195190184
32°F252243236231225220215211204
28°F288276268260255249243236228
24°F329316306298290282276269258
20°F365349340332326317309300290
16°F365365365365358347338332319

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
90% of years
16°F or colder
59% 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
2,722
Cooling degree days, base 65°F
1,813
Growing degree days, base 40°F
8,334
Growing degree days, base 45°F
6,705
Growing degree days, base 50°F
5,228
Growing degree days, base 55°F
3,918
Growing degree days, base 60°F
2,772

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January632156
February494163
March35012187
April14747356
May29173609
June1350799
July0470935
August0429894
September9258699
October12563409
November3688152
December569269

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 5.1 km from Warren County. 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 USC00099141 (Warrenton). Public domain.