Calvert climate

Calvert Frost Dates and Growing Season

NOAA 1991-2020 normals for Franklin, 18.7 km from Calvert, elevation 467 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Franklin. 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 February 28 and the first fall freeze around November 28, a growing season of about 277 days.

Median at 36°F
last March 13, first November 17
Median at 32°F
last February 28, first November 28
Median at 28°F
last February 6, first December 14

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°FApr 4Mar 30Mar 23Mar 17Mar 13Mar 8Mar 4Feb 27Feb 21
32°FMar 21Mar 14Mar 8Mar 4Feb 28Feb 24Feb 16Feb 6Jan 26
28°FMar 9Mar 2Feb 24Feb 14Feb 6Jan 30Jan 24Jan 16Jan 5
24°FFeb 26Feb 13Feb 2Jan 28Jan 21Jan 14Jan 8Dec 31Dec 21
20°FFeb 11Feb 1Jan 25Jan 18Jan 13Jan 7Jan 4Dec 31Dec 18
16°FJan 31Jan 21Jan 19Jan 11Jan 7Jan 5Jan 3Jan 1Dec 18

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°FNov 1Nov 4Nov 8Nov 13Nov 17Nov 21Nov 25Dec 1Dec 6
32°FNov 6Nov 13Nov 18Nov 23Nov 28Dec 3Dec 7Dec 14Dec 25
28°FNov 17Nov 25Dec 1Dec 7Dec 14Dec 22Dec 29Jan 5Jan 13
24°FNov 26Dec 6Dec 17Dec 25Jan 1Jan 4Jan 9Jan 16Jan 29
20°FDec 10Dec 24Dec 31Jan 2Jan 5Jan 8Jan 12Jan 18Feb 1
16°FDec 17Dec 31Jan 1Jan 4Jan 5Jan 8Jan 11Jan 18Jan 25

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°F277268260254248241237230220
32°F312300292285277270263254243
28°F353338329320310303294284271
24°F365365365356347338330319303
20°F365365365365365365363352337
16°F365365365365365365365365365

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
97% of years
24°F or colder
74% of years
20°F or colder
37% of years
16°F or colder
12% 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
1,764
Cooling degree days, base 65°F
2,864
Growing degree days, base 40°F
10,273
Growing degree days, base 45°F
8,538
Growing degree days, base 50°F
6,897
Growing degree days, base 55°F
5,396
Growing degree days, base 60°F
4,049

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January4806115
February32417169
March18746341
April55134531
May5310770
June0496946
July05891,054
August06031,067
September2423871
October48186606
November22843292
December43411136

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 18.7 km from Calvert. 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 USC00413321 (Franklin). Public domain.