Clinton Frost Dates and Growing Season

NOAA 1991-2020 normals for Potomac, 16.6 km from Clinton, elevation 3690 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Potomac. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

NOAA does not state freeze dates for this station.

Median at 28°F: last June 2, first September 4

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Jun 27	Jun 18	Jun 11	Jun 6	Jun 2	May 30	May 28	May 25	May 20
24°F	May 31	May 26	May 24	May 21	May 18	May 16	May 14	May 11	May 7
20°F	May 17	May 14	May 11	May 9	May 7	May 5	May 2	Apr 30	Apr 23
16°F	May 9	May 4	May 1	Apr 28	Apr 24	Apr 19	Apr 12	Apr 5	Mar 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Aug 18	Aug 25	Aug 29	Sep 1	Sep 4	Sep 8	Sep 11	Sep 15	Sep 21
24°F	Sep 5	Sep 11	Sep 15	Sep 19	Sep 22	Sep 25	Sep 28	Oct 1	Oct 5
20°F	Sep 22	Sep 26	Sep 30	Oct 2	Oct 5	Oct 7	Oct 10	Oct 14	Oct 19
16°F	Oct 1	Oct 5	Oct 9	Oct 12	Oct 16	Oct 19	Oct 22	Oct 27	Nov 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	35	29	25	22	20	18	16	14	12
32°F	75	66	59	51	45	41	36	32	27
28°F	114	106	100	96	91	85	80	72	62
24°F	142	136	132	128	125	121	117	112	105
20°F	168	161	156	153	149	146	143	139	133
16°F	202	193	188	182	177	172	167	161	152

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: 9,385
Cooling degree days, base 65°F: 53
Growing degree days, base 40°F: 2,483
Growing degree days, base 45°F: 1,672
Growing degree days, base 50°F: 1,019
Growing degree days, base 55°F: 527
Growing degree days, base 60°F: 208

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,425	0	0
February	1,211	0	0
March	1,039	0	0
April	786	0	4
May	560	0	54
June	310	4	169
July	145	30	352
August	165	18	323
September	406	1	109
October	794	0	8
November	1,118	0	0
December	1,429	0	0

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

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00246685 (Potomac). Public domain.