Grassflat climate

Grassflat Frost Dates and Growing Season

NOAA 1991-2020 normals for Clarence, 15.4 km from Grassflat, elevation 1390 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Clarence. 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 May 21 and the first fall freeze around September 27, a growing season of about 130 days.

Median at 36°F
last May 31, first September 15
Median at 32°F
last May 21, first September 27
Median at 28°F
last May 7, first October 8

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°FJun 15Jun 8Jun 5Jun 2May 31May 29May 26May 22May 15
32°FJun 1May 30May 27May 24May 21May 17May 12May 7Apr 30
28°FMay 27May 22May 17May 12May 7May 3Apr 30Apr 25Apr 21
24°FMay 16May 9May 4Apr 30Apr 25Apr 21Apr 17Apr 12Apr 7
20°FMay 3Apr 20Apr 15Apr 11Apr 8Apr 4Apr 2Mar 31Mar 26
16°FApr 8Apr 3Apr 1Mar 30Mar 28Mar 24Mar 21Mar 18Mar 13

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

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°F130122116111106101979283
32°F154146139135130126121117109
28°F179170164159153148142136128
24°F207199192186181175169162152
20°F235228222218213208202195183
16°F260253246242238234229225217

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
7,131
Cooling degree days, base 65°F
299
Growing degree days, base 40°F
4,059
Growing degree days, base 45°F
3,009
Growing degree days, base 50°F
2,104
Growing degree days, base 55°F
1,340
Growing degree days, base 60°F
727

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28900
February1,11801
March976010
April593052
May31811203
June9053414
July33115547
August5087502
September20430284
October521382
November82807
December1,11001

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 15.4 km from Grassflat. 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 USC00361480 (Clarence). Public domain.