Garrison climate

Garrison Frost Dates and Growing Season

NOAA 1991-2020 normals for Md Sci Ctr Baltimore, 19 km from Garrison, elevation 20 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Md Sci Ctr Baltimore. 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 March 24 and the first fall freeze around November 21, a growing season of about 244 days.

Median at 36°F
last April 3, first November 10
Median at 32°F
last March 24, first November 21
Median at 28°F
last March 11, first December 5

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 15Apr 10Apr 8Apr 5Apr 3Apr 1Mar 31Mar 27Mar 22
32°FApr 4Apr 1Mar 29Mar 27Mar 24Mar 20Mar 17Mar 13Mar 8
28°FMar 26Mar 21Mar 17Mar 15Mar 11Mar 9Mar 6Mar 2Feb 24
24°FMar 16Mar 11Mar 8Mar 5Mar 2Feb 28Feb 23Feb 18Feb 9
20°FMar 6Mar 1Feb 26Feb 20Feb 15Feb 9Feb 5Jan 31Jan 19
16°FFeb 25Feb 18Feb 11Feb 6Feb 2Jan 29Jan 22Jan 16Jan 8

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 29Nov 1Nov 4Nov 7Nov 10Nov 12Nov 15Nov 18Nov 24
32°FNov 7Nov 11Nov 15Nov 18Nov 21Nov 25Nov 29Dec 2Dec 8
28°FNov 18Nov 24Nov 28Dec 2Dec 5Dec 9Dec 14Dec 19Dec 25
24°FDec 1Dec 8Dec 13Dec 19Dec 23Dec 26Dec 31Jan 5Jan 12
20°FDec 11Dec 20Dec 26Dec 31Jan 4Jan 8Jan 12Jan 17Jan 28
16°FDec 23Dec 31Jan 5Jan 9Jan 13Jan 17Jan 23Jan 29Feb 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°F241233229225221217214209202
32°F268259253249244240236230224
28°F294286280275270265259254247
24°F319309303298294289283277269
20°F344332326320315310305300295
16°F365365355345336331325318310

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
98% of years
16°F or colder
81% 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
3,858
Cooling degree days, base 65°F
1,749
Growing degree days, base 40°F
7,431
Growing degree days, base 45°F
5,976
Growing degree days, base 50°F
4,686
Growing degree days, base 55°F
3,553
Growing degree days, base 60°F
2,575

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January873010
February718016
March562374
April25429250
May70130526
June4351797
July0511976
August0439904
September15238673
October17946340
November448198
December735023

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 19 km from Garrison. 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 USW00093784 (Md Sci Ctr Baltimore). Public domain.