Seneca climate

Seneca Frost Dates and Growing Season

NOAA 1991-2020 normals for Centralia, 13.3 km from Seneca, elevation 1320 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Centralia. 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 19 and the first fall freeze around October 19, a growing season of about 182 days.

Median at 36°F
last April 28, first October 9
Median at 32°F
last April 19, first October 19
Median at 28°F
last April 9, first October 30

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 10May 5May 3Apr 30Apr 28Apr 26Apr 23Apr 19Apr 15
32°FMay 3Apr 29Apr 25Apr 22Apr 19Apr 16Apr 12Apr 9Apr 4
28°FApr 25Apr 19Apr 15Apr 11Apr 9Apr 6Apr 3Mar 31Mar 25
24°FApr 16Apr 9Apr 6Apr 2Mar 31Mar 28Mar 25Mar 20Mar 12
20°FApr 5Mar 31Mar 28Mar 24Mar 21Mar 16Mar 13Mar 8Mar 4
16°FMar 29Mar 23Mar 18Mar 14Mar 11Mar 7Mar 4Feb 28Feb 22

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 25Sep 30Oct 4Oct 6Oct 9Oct 12Oct 15Oct 18Oct 22
32°FOct 3Oct 9Oct 13Oct 16Oct 19Oct 22Oct 24Oct 28Nov 1
28°FOct 13Oct 20Oct 23Oct 26Oct 30Nov 1Nov 4Nov 7Nov 11
24°FOct 23Oct 29Nov 1Nov 4Nov 6Nov 10Nov 13Nov 16Nov 23
20°FOct 30Nov 4Nov 8Nov 11Nov 15Nov 19Nov 23Nov 28Dec 3
16°FNov 5Nov 13Nov 17Nov 22Nov 26Nov 29Dec 3Dec 7Dec 14

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°F183177172168163160155150144
32°F202196191186182178174169161
28°F224215210206202197192187180
24°F245236230225221216212207199
20°F266257250244239234230224215
16°F284277270264259253248241232

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
5,375
Cooling degree days, base 65°F
1,304
Growing degree days, base 40°F
6,256
Growing degree days, base 45°F
5,015
Growing degree days, base 50°F
3,902
Growing degree days, base 55°F
2,903
Growing degree days, base 60°F
2,038

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,16400
February92706
March699154
April36214177
May11489443
June9273714
July0408873
August3341803
September61151542
October30826242
November686145
December1,04103

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 13.3 km from Seneca. 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 USC00141408 (Centralia). Public domain.