Forreston climate

Forreston Frost Dates and Growing Season

NOAA 1991-2020 normals for Polo 5NW, 10.4 km from Forreston, elevation 856 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Polo 5NW. 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 29 and the first fall freeze around October 7, a growing season of about 161 days.

Median at 36°F
last May 9, first September 28
Median at 32°F
last April 29, first October 7
Median at 28°F
last April 19, first October 19

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

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°F161155151147142138134130121
32°F180174170165161156152147138
28°F204197192187183178173168160
24°F230220215210206202198193185
20°F252244239234230225221216209
16°F271264258253250245241235228

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
6,466
Cooling degree days, base 65°F
799
Growing degree days, base 40°F
5,211
Growing degree days, base 45°F
4,078
Growing degree days, base 50°F
3,067
Growing degree days, base 55°F
2,180
Growing degree days, base 60°F
1,420

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,34200
February1,09901
March849128
April4735103
May18061355
June24189615
July5254715
August11197651
September11282424
October41111152
November788021
December1,17303

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 10.4 km from Forreston. 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 USC00116897 (Polo 5NW). Public domain.