Stevenson climate

Stevenson Frost Dates and Growing Season

NOAA 1991-2020 normals for Bridgeport 5 Nw, 12.7 km from Stevenson, elevation 664 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bridgeport 5 Nw. 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 7 and the first fall freeze around October 31, a growing season of about 208 days.

Median at 36°F
last April 19, first October 22
Median at 32°F
last April 7, first October 31
Median at 28°F
last March 24, first November 10

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 6Apr 30Apr 27Apr 22Apr 19Apr 16Apr 13Apr 8Apr 3
32°FApr 28Apr 21Apr 16Apr 11Apr 7Apr 3Mar 30Mar 26Mar 18
28°FApr 16Apr 5Apr 1Mar 28Mar 24Mar 20Mar 15Mar 10Mar 2
24°FMar 31Mar 23Mar 17Mar 14Mar 9Mar 4Feb 28Feb 23Feb 13
20°FMar 16Mar 8Mar 1Feb 26Feb 20Feb 13Feb 7Feb 1Jan 23
16°FMar 2Feb 23Feb 12Feb 6Feb 1Jan 30Jan 22Jan 14Jan 5

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 9Oct 14Oct 17Oct 20Oct 22Oct 24Oct 27Oct 30Nov 3
32°FOct 18Oct 22Oct 26Oct 28Oct 31Nov 1Nov 5Nov 8Nov 14
28°FOct 27Nov 1Nov 4Nov 7Nov 10Nov 13Nov 16Nov 21Nov 30
24°FNov 5Nov 10Nov 15Nov 19Nov 23Nov 30Dec 2Dec 8Dec 17
20°FNov 16Nov 24Dec 1Dec 4Dec 10Dec 17Dec 25Jan 1Jan 11
16°FDec 1Dec 9Dec 18Dec 26Dec 31Jan 4Jan 10Jan 18Jan 31

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°F206200194190186182178173166
32°F232224217212208204199192184
28°F261251243238233227222216207
24°F294282274267262257250242232
20°F331319309302296288282272261
16°F365350340334327320311303289

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
99% of years
16°F or colder
92% 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
3,604
Cooling degree days, base 65°F
1,424
Growing degree days, base 40°F
7,282
Growing degree days, base 45°F
5,792
Growing degree days, base 50°F
4,459
Growing degree days, base 55°F
3,289
Growing degree days, base 60°F
2,276

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January814017
February627029
March4563122
April21524282
May57117526
June4280726
July0391856
August1366831
September19205636
October19935318
November485393
December729127

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 12.7 km from Stevenson. 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 USC00011099 (Bridgeport 5 Nw). Public domain.