Smithsburg climate

Smithsburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Catoctin Mtn Park, 7.8 km from Smithsburg, elevation 1610 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Catoctin Mtn Park. 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 14 and the first fall freeze around October 30, a growing season of about 197 days.

Median at 36°F
last April 27, first October 20
Median at 32°F
last April 14, first October 30
Median at 28°F
last April 4, first November 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°FMay 12May 5May 2Apr 29Apr 27Apr 24Apr 21Apr 18Apr 13
32°FApr 30Apr 24Apr 21Apr 18Apr 14Apr 11Apr 9Apr 5Apr 2
28°FApr 17Apr 12Apr 9Apr 6Apr 4Apr 2Mar 31Mar 29Mar 23
24°FApr 7Apr 3Apr 1Mar 29Mar 26Mar 23Mar 19Mar 16Mar 10
20°FMar 29Mar 25Mar 22Mar 18Mar 15Mar 12Mar 9Mar 4Feb 26
16°FMar 22Mar 17Mar 12Mar 8Mar 5Mar 2Feb 27Feb 22Feb 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 5Oct 10Oct 13Oct 17Oct 20Oct 22Oct 25Oct 28Nov 1
32°FOct 14Oct 20Oct 24Oct 27Oct 30Nov 1Nov 3Nov 6Nov 11
28°FOct 25Oct 31Nov 3Nov 6Nov 8Nov 11Nov 15Nov 19Nov 26
24°FNov 3Nov 8Nov 13Nov 16Nov 20Nov 25Nov 29Dec 4Dec 11
20°FNov 14Nov 21Nov 26Dec 1Dec 4Dec 8Dec 12Dec 17Dec 25
16°FNov 27Dec 3Dec 8Dec 13Dec 18Dec 22Dec 27Jan 2Jan 9

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°F194187182179175170166161155
32°F215210205201197194189184176
28°F241232226222218214209205197
24°F264256250244239235230225217
20°F290281275269264259253248238
16°F310302296291287282276270262

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
5,088
Cooling degree days, base 65°F
898
Growing degree days, base 40°F
5,842
Growing degree days, base 45°F
4,565
Growing degree days, base 50°F
3,429
Growing degree days, base 55°F
2,434
Growing degree days, base 60°F
1,587

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,05505
February88306
March727241
April35820182
May13965394
June26176600
July2285749
August6232691
September6499487
October30717214
November610151
December911011

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 7.8 km from Smithsburg. 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 USC00181530 (Catoctin Mtn Park). Public domain.