Merrill climate

Merrill Frost Dates and Growing Season

NOAA 1991-2020 normals for Tulelake, 12.6 km from Merrill, elevation 4038 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tulelake. 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 June 6 and the first fall freeze around September 14, a growing season of about 97 days.

Median at 32°F
last June 6, first September 14
Median at 28°F
last May 16, first September 27

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°F–––––––––
32°FJun 23Jun 18Jun 13Jun 9Jun 6Jun 3May 31May 25May 18
28°FJun 7Jun 1May 26May 20May 16May 12May 8May 4Apr 29
24°FMay 18May 12May 5May 2Apr 29Apr 27Apr 24Apr 21Apr 16
20°FApr 30Apr 24Apr 20Apr 17Apr 14Apr 11Apr 8Apr 4Mar 28
16°FApr 14Apr 8Apr 3Mar 31Mar 26Mar 20Mar 15Mar 9Feb 28

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°F–––––––––
32°FAug 30Sep 4Sep 8Sep 11Sep 14Sep 16Sep 19Sep 22Sep 26
28°FSep 12Sep 17Sep 21Sep 24Sep 27Sep 29Oct 2Oct 5Oct 10
24°FSep 27Oct 1Oct 3Oct 6Oct 9Oct 12Oct 15Oct 20Oct 25
20°FOct 7Oct 13Oct 16Oct 19Oct 23Oct 26Oct 29Nov 2Nov 8
16°FOct 19Oct 25Oct 30Nov 2Nov 6Nov 10Nov 14Nov 19Nov 25

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°F898277726762565042
32°F1191121071029793888375
28°F154146141135131125119113104
24°F183176171167163159154149140
20°F213205200195190186181175169
16°F256243236229223219213207198

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
6,574
Cooling degree days, base 65°F
193
Growing degree days, base 40°F
3,744
Growing degree days, base 45°F
2,656
Growing degree days, base 50°F
1,779
Growing degree days, base 55°F
1,078
Growing degree days, base 60°F
540

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02600
February84400
March78703
April618027
May3753147
June18723294
July4397519
August6160464
September20911263
October526060
November82803
December1,06900

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 12.6 km from Merrill. 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 USC00049053 (Tulelake). Public domain.