Confluence climate

Confluence Frost Dates and Growing Season

NOAA 1991-2020 normals for Confluence 1 Sw Dam, 1.7 km from Confluence, elevation 1490 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Confluence 1 Sw 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 April 30 and the first fall freeze around October 18, a growing season of about 171 days.

Median at 36°F
last May 11, first October 7
Median at 32°F
last April 30, first October 18
Median at 28°F
last April 18, first October 29

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 28May 22May 17May 14May 11May 7May 4May 1Apr 27
32°FMay 18May 11May 6May 2Apr 30Apr 27Apr 24Apr 20Apr 17
28°FMay 2Apr 28Apr 24Apr 21Apr 18Apr 15Apr 11Apr 7Apr 2
24°FApr 18Apr 14Apr 10Apr 6Apr 4Apr 2Mar 31Mar 26Mar 21
20°FApr 8Apr 4Apr 1Mar 29Mar 25Mar 21Mar 18Mar 15Mar 10
16°FApr 1Mar 27Mar 23Mar 19Mar 17Mar 14Mar 10Mar 6Mar 1

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°FSep 23Sep 28Oct 1Oct 4Oct 7Oct 11Oct 14Oct 17Oct 22
32°FOct 4Oct 7Oct 12Oct 15Oct 18Oct 21Oct 23Oct 27Oct 31
28°FOct 14Oct 19Oct 23Oct 25Oct 29Oct 31Nov 1Nov 5Nov 10
24°FOct 23Oct 29Nov 1Nov 3Nov 6Nov 9Nov 13Nov 16Nov 21
20°FNov 2Nov 7Nov 10Nov 14Nov 17Nov 20Nov 24Nov 29Dec 5
16°FNov 12Nov 18Nov 22Nov 27Dec 1Dec 5Dec 10Dec 17Dec 24

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°F168162157153149145141135127
32°F190184179174171166161156149
28°F212206201197192188184179172
24°F236229225220216213209204197
20°F261253246242237233228223215
16°F287278271265261256251244236

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
5,916
Cooling degree days, base 65°F
631
Growing degree days, base 40°F
5,092
Growing degree days, base 45°F
3,907
Growing degree days, base 50°F
2,870
Growing degree days, base 55°F
1,980
Growing degree days, base 60°F
1,230

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,15202
February97203
March836021
April4674109
May20940311
June41123533
July6210670
August12179632
September10168420
October4038142
November722022
December99805

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

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00361705 (Confluence 1 Sw Dam). Public domain.