Monticello climate

Monticello Frost Dates and Growing Season

NOAA 1991-2020 normals for Cascade, 15.9 km from Monticello, elevation 814 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cascade. 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 April 28 and the first fall freeze around October 10, a growing season of about 164 days.

Median at 36°F
last May 6, first September 30
Median at 32°F
last April 28, first October 10
Median at 28°F
last April 15, first October 20

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 21May 16May 13May 10May 6May 4May 1Apr 29Apr 24
32°FMay 12May 6May 3Apr 30Apr 28Apr 24Apr 21Apr 17Apr 12
28°FMay 2Apr 28Apr 22Apr 19Apr 15Apr 13Apr 9Apr 6Apr 1
24°FApr 21Apr 15Apr 11Apr 8Apr 5Apr 3Mar 31Mar 28Mar 21
20°FApr 12Apr 6Apr 2Mar 31Mar 27Mar 23Mar 19Mar 15Mar 10
16°FApr 2Mar 28Mar 23Mar 19Mar 15Mar 13Mar 10Mar 6Mar 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°FSep 17Sep 22Sep 25Sep 28Sep 30Oct 2Oct 5Oct 8Oct 12
32°FSep 28Oct 1Oct 4Oct 7Oct 10Oct 11Oct 14Oct 16Oct 21
28°FOct 7Oct 12Oct 15Oct 18Oct 20Oct 22Oct 24Oct 27Nov 1
24°FOct 17Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 8Nov 13
20°FOct 29Nov 1Nov 4Nov 7Nov 11Nov 14Nov 18Nov 22Nov 27
16°FNov 7Nov 11Nov 15Nov 18Nov 21Nov 25Nov 29Dec 2Dec 7

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°F162157153150146142138134129
32°F184177172168164160155152146
28°F206200195191186181177172165
24°F230222216211207202198193186
20°F251243238233229224219214206
16°F272263258253249245240235227

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
6,944
Cooling degree days, base 65°F
741
Growing degree days, base 40°F
4,943
Growing degree days, base 45°F
3,858
Growing degree days, base 50°F
2,894
Growing degree days, base 55°F
2,051
Growing degree days, base 60°F
1,331

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41400
February1,16900
March914118
April517485
May21347316
June31172591
July7250708
August13188640
September13173398
October4687120
November837016
December1,23201

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 15.9 km from Monticello. 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 USC00131257 (Cascade). Public domain.