Monticello climate

Monticello Frost Dates and Growing Season

NOAA 1991-2020 normals for Monticello 2E, 3.1 km from Monticello, elevation 6820 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Monticello 2E. 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 19 and the first fall freeze around October 2, a growing season of about 133 days.

Median at 36°F
last June 1, first September 24
Median at 32°F
last May 19, first October 2
Median at 28°F
last May 6, first October 12

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 17Jun 12Jun 7Jun 4Jun 1May 30May 27May 23May 18
32°FJun 6May 31May 27May 23May 19May 16May 13May 9May 3
28°FMay 23May 17May 13May 9May 6May 2Apr 30Apr 25Apr 21
24°FMay 12May 4Apr 30Apr 26Apr 22Apr 18Apr 14Apr 10Apr 5
20°FApr 26Apr 17Apr 12Apr 8Apr 5Apr 2Mar 29Mar 21Mar 13
16°FApr 7Apr 1Mar 26Mar 21Mar 16Mar 11Mar 7Mar 4Feb 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°FSep 11Sep 16Sep 19Sep 21Sep 24Sep 26Sep 28Oct 1Oct 5
32°FSep 20Sep 24Sep 28Oct 1Oct 2Oct 5Oct 7Oct 10Oct 15
28°FSep 28Oct 2Oct 6Oct 9Oct 12Oct 15Oct 18Oct 20Oct 24
24°FOct 5Oct 12Oct 16Oct 19Oct 22Oct 25Oct 29Nov 2Nov 6
20°FOct 19Oct 24Oct 28Oct 31Nov 3Nov 6Nov 9Nov 13Nov 16
16°FOct 30Nov 3Nov 7Nov 10Nov 13Nov 16Nov 19Nov 22Nov 27

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°F1311241191161121081049993
32°F154147142137133129125120113
28°F177171166161158153148142134
24°F204196190185181176171166158
20°F237227219213208203198193184
16°F266258251245240236229221213

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
6,877
Cooling degree days, base 65°F
315
Growing degree days, base 40°F
4,070
Growing degree days, base 45°F
3,012
Growing degree days, base 50°F
2,116
Growing degree days, base 55°F
1,365
Growing degree days, base 60°F
764

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,21700
February97900
March83702
April596029
May3464165
June8854417
July9147603
August1997542
September16814304
October539052
November87301
December1,20600

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 3.1 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 USC00425805 (Monticello 2E). Public domain.