Leesburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Leesburg Muni AP, 6.7 km from Leesburg, elevation 77 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Leesburg Muni AP. 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 January 26 and the first fall freeze around January 9, a growing season of about 346 days.

Median at 36°F: last February 6, first December 30
Median at 32°F: last January 26, first January 9
Median at 28°F: last January 17, first January 13

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Mar 8	Feb 28	Feb 21	Feb 14	Feb 6	Jan 31	Jan 26	Jan 18	Jan 7
32°F	Feb 21	Feb 11	Feb 3	Jan 31	Jan 26	Jan 17	Jan 12	Jan 7	Dec 31
28°F	Feb 9	Feb 3	Jan 30	Jan 22	Jan 17	Jan 13	Jan 9	Jan 5	Dec 29
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Dec 1	Dec 7	Dec 16	Dec 24	Dec 30	Jan 3	Jan 8	Jan 14	Jan 25
32°F	Dec 17	Dec 27	Jan 1	Jan 5	Jan 9	Jan 14	Jan 20	Jan 28	Feb 5
28°F	Dec 28	Jan 2	Jan 6	Jan 10	Jan 13	Jan 19	Jan 23	Feb 1	Feb 8
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	352	338	331	321	314	308	301	292	281
32°F	365	365	362	355	346	338	332	323	312
28°F	365	365	365	365	365	365	365	354	337
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder: 96% of years
32°F or colder: 67% of years
28°F or colder: 26% of years
24°F or colder: 4% of years
20°F or colder: 0% of years
16°F or colder: 0% 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: 629
Cooling degree days, base 65°F: 3,482
Growing degree days, base 40°F: 11,979
Growing degree days, base 45°F: 10,161
Growing degree days, base 50°F: 8,365
Growing degree days, base 55°F: 6,624
Growing degree days, base 60°F: 4,982

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	212	38	312
February	126	60	360
March	64	116	517
April	12	228	666
May	0	400	865
June	0	507	957
July	0	558	1,023
August	0	569	1,034
September	0	492	942
October	7	326	784
November	55	121	517
December	154	67	388

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 6.7 km from Leesburg. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00012819 (Leesburg Muni AP). Public domain.