Bow Mar climate

Bow Mar Frost Dates and Growing Season

NOAA 1991-2020 normals for Marston Fltr Plt, 1.5 km from Bow Mar, elevation 5610 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Marston Fltr Plt. 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 May 2 and the first fall freeze around October 11, a growing season of about 160 days.

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

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°FSep 17Sep 23Sep 27Sep 30Oct 2Oct 4Oct 7Oct 11Oct 15
32°FSep 27Oct 1Oct 5Oct 7Oct 11Oct 14Oct 17Oct 19Oct 23
28°FOct 6Oct 11Oct 15Oct 18Oct 21Oct 24Oct 27Oct 31Nov 5
24°FOct 15Oct 20Oct 24Oct 27Oct 30Nov 2Nov 6Nov 10Nov 14
20°FOct 20Oct 26Nov 1Nov 4Nov 8Nov 12Nov 16Nov 20Nov 24
16°FOct 26Nov 2Nov 9Nov 13Nov 17Nov 21Nov 24Nov 27Dec 3

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°F160154149146142137132127120
32°F181174169164160156151146139
28°F200193188184180176172166160
24°F224217210205200196191184177
20°F250240233227222217211204195
16°F273263257251244238231224215

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
5,822
Cooling degree days, base 65°F
659
Growing degree days, base 40°F
5,004
Growing degree days, base 45°F
3,796
Growing degree days, base 50°F
2,772
Growing degree days, base 55°F
1,918
Growing degree days, base 60°F
1,216

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,00601
February88504
March733026
April532170
May28417241
June58121514
July5251711
August12206659
September12462399
October4522120
November734026
December99802

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 1.5 km from Bow Mar. 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 USC00055402 (Marston Fltr Plt). Public domain.