Upland Frost Dates and Growing Season

NOAA 1991-2020 normals for Ontario Intl AP, 6.4 km from Upland, elevation 949 ft

Frost and the growing season

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

A freeze (32°F or colder) happens in only 41 percent of years at Ontario Intl AP, so there is no typical freeze season.

Median at 36°F: last January 27, first December 17
Median at 32°F: last January 4, first December 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Feb 28	Feb 20	Feb 11	Feb 3	Jan 27	Jan 17	Jan 8	Jan 1	Dec 24
32°F	Feb 7	Jan 25	Jan 13	Jan 8	Jan 4	Dec 31	Dec 27	Dec 21	Dec 14
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

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	Nov 27	Dec 4	Dec 9	Dec 13	Dec 17	Dec 21	Dec 25	Jan 2	Jan 17
32°F	Dec 11	Dec 18	Dec 22	Dec 25	Dec 30	Jan 3	Jan 7	Jan 15	Feb 1
28°F	–	–	–	–	–	–	–	–	–
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

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	358	349	341	334	327	317	307	298	282
32°F	365	365	365	365	365	365	359	351	339
28°F	365	365	365	365	365	365	365	365	365
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder: 93% of years
32°F or colder: 41% of years
28°F or colder: 4% of years
24°F or colder: 0% of years
20°F or colder: 0% of years
16°F or colder: 0% 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: 1,293
Cooling degree days, base 65°F: 1,970
Growing degree days, base 40°F: 9,802
Growing degree days, base 45°F: 7,979
Growing degree days, base 50°F: 6,189
Growing degree days, base 55°F: 4,528
Growing degree days, base 60°F: 3,103

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	280	5	202
February	228	8	207
March	172	23	319
April	105	57	403
May	37	121	549
June	4	250	696
July	0	442	907
August	0	467	932
September	1	378	826
October	26	177	615
November	135	40	357
December	304	2	177

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 6.4 km from Upland. 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 USW00003102 (Ontario Intl AP). Public domain.