Twisp climate

Twisp Frost Dates and Growing Season

NOAA 1991-2020 normals for Winthrop 1 Wsw, 13.2 km from Twisp, elevation 1749 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Winthrop 1 Wsw. 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 15 and the first fall freeze around September 22, a growing season of about 127 days.

Median at 36°F
last June 1, first September 9
Median at 32°F
last May 15, first September 22
Median at 28°F
last May 1, first October 3

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 18Jun 12Jun 8Jun 4Jun 1May 30May 26May 22May 16
32°FJun 1May 27May 22May 19May 15May 13May 9May 6Apr 30
28°FMay 15May 9May 6May 3May 1Apr 28Apr 26Apr 22Apr 17
24°FApr 30Apr 24Apr 19Apr 15Apr 10Apr 7Apr 3Mar 31Mar 25
20°FApr 5Apr 1Mar 28Mar 24Mar 20Mar 17Mar 14Mar 11Mar 7
16°FMar 21Mar 16Mar 13Mar 10Mar 8Mar 6Mar 4Mar 1Feb 26

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 30Sep 2Sep 4Sep 7Sep 9Sep 11Sep 14Sep 17Sep 21
32°FSep 10Sep 14Sep 17Sep 19Sep 22Sep 24Sep 27Sep 29Oct 2
28°FSep 22Sep 27Sep 30Oct 1Oct 3Oct 5Oct 8Oct 12Oct 17
24°FOct 3Oct 6Oct 10Oct 13Oct 16Oct 19Oct 22Oct 26Oct 31
20°FOct 13Oct 19Oct 24Oct 27Oct 30Nov 1Nov 5Nov 10Nov 16
16°FOct 26Oct 31Nov 4Nov 7Nov 11Nov 14Nov 18Nov 22Nov 28

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°F12011310810410095918679
32°F146140136132127123118114107
28°F173167163159156152148142136
24°F211203197191187183178172165
20°F245237230226221215210206199
16°F268261256252247243238232224

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
7,314
Cooling degree days, base 65°F
302
Growing degree days, base 40°F
3,908
Growing degree days, base 45°F
2,874
Growing degree days, base 50°F
1,998
Growing degree days, base 55°F
1,265
Growing degree days, base 60°F
692

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,31300
February1,03000
March84601
April551034
May3025190
June14130340
July31133567
August38114541
September19720280
October577043
November96500
December1,32400

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 13.2 km from Twisp. 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 USC00459376 (Winthrop 1 Wsw). Public domain.