Mecca Frost Dates and Growing Season

NOAA 1991-2020 normals for Mecca Fire Stn, 0.5 km from Mecca, elevation -183 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mecca Fire Stn. 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 January 6 and the first fall freeze around December 22, a growing season of about 352 days.

Median at 36°F: last January 28, first December 10
Median at 32°F: last January 6, first December 22
Median at 28°F: last January 7, first January 1

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 17	Feb 10	Feb 5	Feb 1	Jan 28	Jan 21	Jan 14	Jan 7	Dec 30
32°F	Feb 4	Jan 26	Jan 18	Jan 12	Jan 6	Jan 2	Dec 29	Dec 23	Dec 13
28°F	Feb 2	Jan 23	Jan 14	Jan 11	Jan 7	Jan 2	Dec 31	Dec 26	Dec 18
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 25	Nov 30	Dec 3	Dec 7	Dec 10	Dec 13	Dec 16	Dec 20	Dec 28
32°F	Dec 4	Dec 9	Dec 14	Dec 18	Dec 22	Dec 26	Dec 31	Jan 3	Jan 14
28°F	Dec 10	Dec 22	Dec 26	Dec 31	Jan 1	Jan 5	Jan 10	Jan 16	Jan 29
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	347	338	331	325	318	311	305	298	287
32°F	365	365	365	358	352	345	340	332	321
28°F	365	365	365	365	365	365	365	364	350
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: 97% of years
32°F or colder: 70% of years
28°F or colder: 21% of years
24°F or colder: 3% 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: 836
Cooling degree days, base 65°F: 4,404
Growing degree days, base 40°F: 12,693
Growing degree days, base 45°F: 10,870
Growing degree days, base 50°F: 9,062
Growing degree days, base 55°F: 7,329
Growing degree days, base 60°F: 5,764

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	247	4	228
February	145	20	297
March	45	116	536
April	7	249	692
May	1	480	944
June	0	672	1,122
July	0	877	1,342
August	0	874	1,339
September	0	678	1,128
October	3	364	826
November	91	67	427
December	297	2	180

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 0.5 km from Mecca. 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 USC00045502 (Mecca Fire Stn). Public domain.