Hilltop climate

Hilltop Frost Dates and Growing Season

NOAA 1991-2020 normals for Oak Hill, 3.2 km from Hilltop, elevation 2040 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Oak Hill. 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 21 and the first fall freeze around October 19, a growing season of about 179 days.

Median at 36°F
last May 4, first October 11
Median at 32°F
last April 21, first October 19
Median at 28°F
last April 6, first October 30

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 24May 18May 12May 8May 4May 1Apr 28Apr 23Apr 18
32°FMay 13May 5Apr 30Apr 25Apr 21Apr 18Apr 14Apr 10Apr 5
28°FApr 28Apr 18Apr 14Apr 10Apr 6Apr 4Apr 1Mar 30Mar 24
24°FApr 10Apr 5Apr 1Mar 31Mar 28Mar 25Mar 20Mar 17Mar 11
20°FMar 31Mar 28Mar 23Mar 19Mar 17Mar 13Mar 9Mar 3Feb 25
16°FMar 24Mar 18Mar 13Mar 8Mar 4Feb 28Feb 24Feb 18Feb 9

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

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°F177171165161157153148141133
32°F200193188184179174169164156
28°F226217212208204200196191183
24°F253244238233229223219214207
20°F282272264258253248241235227
16°F307298291285280274267260252

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
5,192
Cooling degree days, base 65°F
639
Growing degree days, base 40°F
5,492
Growing degree days, base 45°F
4,213
Growing degree days, base 50°F
3,088
Growing degree days, base 55°F
2,116
Growing degree days, base 60°F
1,293

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,03107
February85707
March722146
April3799167
May17539340
June37128541
July7202660
August8177634
September8276446
October3547179
November637149
December905011

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 3.2 km from Hilltop. 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 USC00466591 (Oak Hill). Public domain.