Julian climate

Julian Frost Dates and Growing Season

NOAA 1991-2020 normals for Julian Cdf, 0.9 km from Julian, elevation 4215 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Julian Cdf. 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 March 27 and the first fall freeze around December 1, a growing season of about 248 days.

Median at 36°F
last April 27, first November 11
Median at 32°F
last March 27, first December 1
Median at 28°F
last February 13, first December 22

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.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 23May 15May 7May 1Apr 27Apr 22Apr 15Apr 7Mar 29
32°FApr 30Apr 19Apr 11Apr 4Mar 27Mar 20Mar 11Mar 1Feb 17
28°FMar 24Mar 10Mar 1Feb 22Feb 13Feb 5Jan 27Jan 15Jan 1
24°FFeb 23Feb 12Feb 7Jan 31Jan 24Jan 17Jan 11Jan 2Dec 26
20°FFeb 12Feb 7Feb 1Jan 28Jan 23Jan 20Jan 12Jan 10Jan 6
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.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 17Oct 26Nov 2Nov 7Nov 11Nov 17Nov 22Nov 28Dec 3
32°FNov 3Nov 14Nov 20Nov 26Dec 1Dec 5Dec 10Dec 15Dec 21
28°FNov 23Dec 4Dec 10Dec 15Dec 22Dec 28Jan 4Jan 16Feb 3
24°FDec 8Dec 25Dec 31Jan 4Jan 10Jan 19Jan 24Feb 2Feb 14
20°FJan 4Jan 9Jan 11Jan 19Jan 22Jan 26Feb 1Feb 5Feb 11
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.

Threshold10%20%30%40%50%60%70%80%90%
36°F234222213207199191184173160
32°F291276265257248240230220206
28°F359344330318309300289278264
24°F365365365365365353341329312
20°F365365365365365365365365361
16°F365365365365365365365365365

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
94% of years
24°F or colder
49% of years
20°F or colder
12% 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
3,528
Cooling degree days, base 65°F
917
Growing degree days, base 40°F
6,608
Growing degree days, base 45°F
5,009
Growing degree days, base 50°F
3,630
Growing degree days, base 55°F
2,499
Growing degree days, base 60°F
1,607

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January594036
February520045
March491183
April3762135
May24825268
June61126516
July3282744
August3286749
September36160575
October18233328
November4012118
December615034

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

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00044412 (Julian Cdf). Public domain.