Mountain Gate Frost Dates and Growing Season

NOAA 1991-2020 normals for Shasta Dam, 7.1 km from Mountain Gate, elevation 1075 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Shasta Dam. 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 February 8 and the first fall freeze around December 28, a growing season of about 322 days.

Median at 36°F: last March 19, first December 6
Median at 32°F: last February 8, first December 28
Median at 28°F: last January 18, first January 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	Apr 16	Apr 7	Apr 1	Mar 27	Mar 19	Mar 10	Mar 1	Feb 20	Feb 6
32°F	Mar 28	Mar 11	Mar 1	Feb 20	Feb 8	Jan 29	Jan 16	Jan 5	Dec 26
28°F	Mar 14	Feb 28	Feb 14	Jan 31	Jan 18	Jan 5	Dec 31	Dec 23	Dec 14
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 16	Nov 23	Nov 28	Dec 2	Dec 6	Dec 10	Dec 14	Dec 21	Dec 30
32°F	Dec 1	Dec 9	Dec 16	Dec 21	Dec 28	Jan 1	Jan 9	Jan 24	Feb 18
28°F	Dec 10	Dec 17	Dec 23	Jan 1	Jan 4	Jan 21	Feb 5	Feb 25	Mar 10
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	313	294	281	271	263	256	249	240	231
32°F	365	357	345	331	322	311	301	285	268
28°F	365	365	365	365	365	365	360	344	321
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: 100% of years
32°F or colder: 87% of years
28°F or colder: 27% of years
24°F or colder: 3% of years
20°F or colder: 1% of years
16°F or colder: 1% 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: 2,582
Cooling degree days, base 65°F: 2,071
Growing degree days, base 40°F: 8,630
Growing degree days, base 45°F: 6,891
Growing degree days, base 50°F: 5,342
Growing degree days, base 55°F: 4,045
Growing degree days, base 60°F: 2,970

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	535	0	40
February	415	0	72
March	356	4	156
April	221	29	273
May	80	147	533
June	15	333	768
July	1	558	1,023
August	0	523	987
September	7	356	799
October	80	117	503
November	328	5	156
December	545	0	33

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 7.1 km from Mountain Gate. 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 USC00048135 (Shasta Dam). Public domain.