Hamilton climate

Hamilton Frost Dates and Growing Season

NOAA 1991-2020 normals for Purcellville, 4.2 km from Hamilton, elevation 510 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Purcellville. 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 16 and the first fall freeze around October 25, a growing season of about 189 days.

Median at 36°F
last May 1, first October 12
Median at 32°F
last April 16, first October 25
Median at 28°F
last April 2, first November 5

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 20May 13May 9May 5May 1Apr 27Apr 24Apr 19Apr 14
32°FMay 7Apr 30Apr 24Apr 19Apr 16Apr 13Apr 9Apr 5Mar 31
28°FApr 17Apr 12Apr 8Apr 5Apr 2Mar 31Mar 30Mar 26Mar 20
24°FApr 5Apr 1Mar 29Mar 25Mar 22Mar 19Mar 15Mar 11Mar 6
20°FMar 25Mar 19Mar 17Mar 13Mar 10Mar 7Mar 4Feb 28Feb 20
16°FMar 17Mar 10Mar 6Mar 2Feb 26Feb 21Feb 15Feb 9Feb 2

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 29Oct 2Oct 5Oct 9Oct 12Oct 16Oct 19Oct 23Oct 27
32°FOct 7Oct 13Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 7
28°FOct 21Oct 27Oct 31Nov 2Nov 5Nov 7Nov 10Nov 14Nov 20
24°FNov 3Nov 7Nov 10Nov 14Nov 17Nov 20Nov 25Nov 30Dec 5
20°FNov 12Nov 18Nov 23Nov 28Dec 1Dec 5Dec 10Dec 16Dec 23
16°FNov 26Dec 2Dec 8Dec 13Dec 18Dec 22Dec 28Jan 2Jan 14

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°F188179174169165160156150141
32°F210204198193189185180175165
28°F236228224219215211207202194
24°F266256250244240236230225217
20°F293284278271266261255248241
16°F321312306300295290284277266

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
4,942
Cooling degree days, base 65°F
1,050
Growing degree days, base 40°F
5,982
Growing degree days, base 45°F
4,690
Growing degree days, base 50°F
3,557
Growing degree days, base 55°F
2,573
Growing degree days, base 60°F
1,737

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,00006
February84106
March700137
April36213164
May14761384
June20207638
July1340804
August3291753
September63122509
October31615202
November610144
December88209

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 4.2 km from Hamilton. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00444909 (Purcellville). Public domain.