Wye climate

Wye Frost Dates and Growing Season

NOAA 1991-2020 normals for Missoula 6 Nw WFO, 3.9 km from Wye, elevation 3197 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Missoula 6 Nw WFO. 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 6 and the first fall freeze around October 4, a growing season of about 151 days.

Median at 36°F
last May 23, first September 25
Median at 32°F
last May 6, first October 4
Median at 28°F
last April 23, first October 15

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°FJun 10Jun 3May 30May 26May 23May 20May 16May 13May 7
32°FMay 19May 15May 11May 8May 6May 3May 1Apr 29Apr 24
28°FMay 7May 2Apr 30Apr 27Apr 23Apr 19Apr 16Apr 12Apr 6
24°FApr 24Apr 16Apr 11Apr 7Apr 3Mar 31Mar 24Mar 18Mar 12
20°FApr 3Mar 28Mar 21Mar 16Mar 12Mar 9Mar 6Mar 2Feb 25
16°FMar 19Mar 12Mar 7Mar 4Mar 2Feb 28Feb 24Feb 18Feb 11

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 11Sep 16Sep 19Sep 22Sep 25Sep 27Sep 29Oct 2Oct 5
32°FSep 23Sep 27Sep 30Oct 2Oct 4Oct 6Oct 8Oct 12Oct 16
28°FOct 3Oct 7Oct 10Oct 12Oct 15Oct 18Oct 21Oct 24Oct 29
24°FOct 12Oct 18Oct 21Oct 24Oct 28Oct 31Nov 2Nov 7Nov 13
20°FOct 20Oct 27Oct 31Nov 3Nov 7Nov 10Nov 15Nov 20Nov 25
16°FOct 28Nov 5Nov 9Nov 13Nov 17Nov 21Nov 25Nov 29Dec 4

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°F142135130127123119114108100
32°F169162158154151148144139134
28°F197188184180176172168163155
24°F233223217212207202196191183
20°F261253247243238233227221212
16°F284275270264258253247242234

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
7,156
Cooling degree days, base 65°F
382
Growing degree days, base 40°F
3,922
Growing degree days, base 45°F
2,896
Growing degree days, base 50°F
2,042
Growing degree days, base 55°F
1,337
Growing degree days, base 60°F
783

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,20800
February98300
March82202
April591028
May3405166
June15338338
July25175615
August34141572
September21123276
October612044
November95701
December1,22100

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 3.9 km from Wye. 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 USC00245740 (Missoula 6 Nw WFO). Public domain.