Frederick County climate

Frederick County Frost Dates and Growing Season

NOAA 1991-2020 normals for Frederick Police Brks, 7.1 km from Frederick County, elevation 380 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Frederick Police Brks. 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 2 and the first fall freeze around November 6, a growing season of about 218 days.

Median at 36°F
last April 15, first October 24
Median at 32°F
last April 2, first November 6
Median at 28°F
last March 21, first November 21

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 25Apr 21Apr 18Apr 15Apr 12Apr 8Apr 5Mar 31
32°FApr 15Apr 11Apr 7Apr 4Apr 2Mar 31Mar 28Mar 23Mar 17
28°FApr 4Mar 31Mar 29Mar 25Mar 21Mar 17Mar 14Mar 10Mar 3
24°FMar 26Mar 20Mar 16Mar 12Mar 9Mar 6Mar 3Feb 28Feb 20
20°FMar 17Mar 10Mar 6Mar 3Feb 28Feb 23Feb 16Feb 9Feb 2
16°FMar 7Mar 1Feb 23Feb 16Feb 10Feb 5Jan 31Jan 24Jan 14

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 9Oct 15Oct 19Oct 21Oct 24Oct 27Oct 30Nov 1Nov 6
32°FOct 23Oct 29Nov 1Nov 4Nov 6Nov 10Nov 13Nov 17Nov 24
28°FNov 6Nov 10Nov 14Nov 17Nov 21Nov 26Dec 1Dec 5Dec 11
24°FNov 14Nov 23Nov 29Dec 2Dec 7Dec 11Dec 16Dec 21Dec 28
20°FDec 1Dec 9Dec 14Dec 20Dec 24Dec 28Jan 1Jan 5Jan 15
16°FDec 15Dec 23Dec 28Jan 1Jan 4Jan 10Jan 15Jan 20Jan 29

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°F213205201197193189184178170
32°F239232227222218214210204196
28°F271261255249245239235230223
24°F298289282277272266261255246
20°F325318309304299294288281273
16°F353340333328322315310304295

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
94% 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
4,275
Cooling degree days, base 65°F
1,397
Growing degree days, base 40°F
6,775
Growing degree days, base 45°F
5,392
Growing degree days, base 50°F
4,174
Growing degree days, base 55°F
3,099
Growing degree days, base 60°F
2,172

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January936010
February75207
March608253
April27726230
May77114503
June8285727
July0419883
August0358823
September31170589
October23922264
November539171
December809014

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 7.1 km from Frederick 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 USC00183348 (Frederick Police Brks). Public domain.