Simpson County climate

Simpson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Portland Sewage Plt, 17.9 km from Simpson County, elevation 794 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Portland Sewage Plt. 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 5 and the first fall freeze around November 1, a growing season of about 210 days.

Median at 36°F
last April 16, first October 23
Median at 32°F
last April 5, first November 1
Median at 28°F
last March 26, first November 11

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 2Apr 27Apr 22Apr 19Apr 16Apr 13Apr 10Apr 6Apr 2
32°FApr 19Apr 13Apr 10Apr 7Apr 5Apr 1Mar 30Mar 27Mar 21
28°FApr 9Apr 4Apr 1Mar 29Mar 26Mar 22Mar 18Mar 13Mar 5
24°FMar 31Mar 26Mar 21Mar 17Mar 13Mar 9Mar 4Feb 28Feb 21
20°FMar 20Mar 14Mar 9Mar 6Mar 2Feb 26Feb 21Feb 13Feb 6
16°FMar 12Mar 5Feb 28Feb 23Feb 16Feb 10Feb 6Jan 31Jan 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°FOct 12Oct 16Oct 19Oct 21Oct 23Oct 25Oct 28Oct 30Nov 3
32°FOct 21Oct 24Oct 27Oct 30Nov 1Nov 3Nov 5Nov 9Nov 14
28°FOct 31Nov 2Nov 5Nov 8Nov 11Nov 14Nov 17Nov 22Nov 29
24°FNov 6Nov 11Nov 15Nov 19Nov 23Nov 27Dec 1Dec 5Dec 10
20°FNov 15Nov 22Nov 29Dec 1Dec 4Dec 8Dec 13Dec 20Dec 28
16°FNov 30Dec 5Dec 10Dec 15Dec 22Dec 27Jan 1Jan 7Jan 17

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°F207201196192188184180176169
32°F231224218215210207203198192
28°F257248242236231227222217211
24°F282272266260255250244238230
20°F308297291285279273267261251
16°F334324315309304298292285274

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
99% 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
3,984
Cooling degree days, base 65°F
1,545
Growing degree days, base 40°F
7,242
Growing degree days, base 45°F
5,815
Growing degree days, base 50°F
4,529
Growing degree days, base 55°F
3,389
Growing degree days, base 60°F
2,393

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January900019
February703129
March5327108
April24236280
May71137533
June4306751
July0423888
August1388852
September26203627
October20741319
November509396
December789028

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 17.9 km from Simpson County. 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 USC00407359 (Portland Sewage Plt). Public domain.