Mullan climate

Mullan Frost Dates and Growing Season

NOAA 1991-2020 normals for Mullan, 0.8 km from Mullan, elevation 3201 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mullan. 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 12 and the first fall freeze around September 30, a growing season of about 138 days.

Median at 36°F
last June 7, first September 15
Median at 32°F
last May 12, first September 30
Median at 28°F
last April 24, first October 14

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°FJul 6Jun 26Jun 18Jun 13Jun 7Jun 1May 27May 22May 14
32°FJun 19Jun 1May 23May 16May 12May 9May 6May 1Apr 26
28°FMay 12May 5Apr 30Apr 27Apr 24Apr 20Apr 16Apr 10Apr 1
24°FApr 23Apr 15Apr 8Apr 3Mar 30Mar 26Mar 21Mar 16Mar 8
20°FApr 1Mar 26Mar 20Mar 16Mar 12Mar 8Mar 5Mar 1Feb 22
16°FMar 19Mar 13Mar 9Mar 5Mar 2Feb 28Feb 22Feb 15Feb 2

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°FAug 31Sep 5Sep 8Sep 11Sep 15Sep 17Sep 22Sep 25Oct 1
32°FSep 12Sep 19Sep 23Sep 27Sep 30Oct 3Oct 6Oct 11Oct 17
28°FSep 27Oct 2Oct 7Oct 11Oct 14Oct 18Oct 22Oct 27Nov 4
24°FOct 8Oct 16Oct 22Oct 27Oct 31Nov 4Nov 9Nov 15Nov 22
20°FOct 23Nov 1Nov 6Nov 12Nov 17Nov 21Nov 24Nov 28Dec 6
16°FNov 3Nov 11Nov 18Nov 23Nov 27Dec 1Dec 4Dec 12Dec 23

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°F1251171101049892867765
32°F16315514914313813112211499
28°F204195186181175170164156144
24°F244233227220214207200191182
20°F279267259253246240233226214
16°F306295286278271264257247236

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
7,417
Cooling degree days, base 65°F
202
Growing degree days, base 40°F
3,358
Growing degree days, base 45°F
2,388
Growing degree days, base 50°F
1,593
Growing degree days, base 55°F
959
Growing degree days, base 60°F
497

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12200
February96700
March88502
April644025
May3855142
June22922255
July8484466
August8474457
September27816214
October639032
November92700
December1,17300

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 0.8 km from Mullan. 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 USC00106230 (Mullan). Public domain.