Sisters Frost Dates and Growing Season

NOAA 1991-2020 normals for Sisters, 0.8 km from Sisters, elevation 3180 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sisters. 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 8, first September 13

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	Jul 3	Jun 25	Jun 18	Jun 14	Jun 8	Jun 2	May 29	May 23	May 17
24°F	Jun 11	May 29	May 20	May 15	May 10	May 6	May 2	Apr 29	Apr 21
20°F	May 11	May 3	Apr 28	Apr 24	Apr 19	Apr 14	Apr 8	Apr 2	Mar 25
16°F	Apr 21	Apr 11	Apr 4	Mar 30	Mar 23	Mar 17	Mar 11	Mar 4	Feb 26

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 25	Sep 1	Sep 5	Sep 9	Sep 13	Sep 17	Sep 21	Sep 25	Oct 1
24°F	Sep 12	Sep 19	Sep 24	Sep 27	Oct 1	Oct 3	Oct 6	Oct 11	Oct 16
20°F	Sep 30	Oct 3	Oct 7	Oct 12	Oct 16	Oct 19	Oct 24	Oct 29	Nov 5
16°F	Oct 12	Oct 18	Oct 23	Oct 27	Oct 31	Nov 3	Nov 8	Nov 16	Nov 26

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	48	41	35	31	28	24	21	18	14
32°F	83	73	67	62	57	51	45	39	33
28°F	127	116	107	102	97	91	84	75	65
24°F	167	159	153	146	140	135	127	119	108
20°F	210	199	192	185	180	174	168	161	149
16°F	254	241	233	227	219	213	205	196	183

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: 7,246
Cooling degree days, base 65°F: 150
Growing degree days, base 40°F: 3,231
Growing degree days, base 45°F: 2,232
Growing degree days, base 50°F: 1,450
Growing degree days, base 55°F: 850
Growing degree days, base 60°F: 415

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,060	0	0
February	899	0	0
March	840	0	3
April	662	0	18
May	456	2	100
June	265	14	221
July	87	71	450
August	102	54	419
September	282	9	204
October	622	0	34
November	872	0	3
December	1,099	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 0.8 km from Sisters. 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 USC00357857 (Sisters). Public domain.