Ulm climate

Ulm Frost Dates and Growing Season

NOAA 1991-2020 normals for Great Falls WFO, 9.8 km from Ulm, elevation 3705 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Great Falls 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 12 and the first fall freeze around September 28, a growing season of about 138 days.

Median at 36°F
last May 27, first September 19
Median at 32°F
last May 12, first September 28
Median at 28°F
last April 30, first October 8

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 11Jun 5Jun 1May 30May 27May 24May 21May 17May 13
32°FMay 27May 21May 18May 15May 12May 9May 7May 4Apr 30
28°FMay 13May 8May 5May 2Apr 30Apr 28Apr 25Apr 20Apr 14
24°FMay 4Apr 30Apr 27Apr 23Apr 19Apr 15Apr 11Apr 8Apr 2
20°FApr 29Apr 21Apr 16Apr 12Apr 8Apr 5Apr 2Mar 29Mar 20
16°FApr 18Apr 11Apr 6Apr 3Mar 31Mar 27Mar 21Mar 15Mar 9

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 3Sep 9Sep 13Sep 16Sep 19Sep 22Sep 24Sep 28Oct 2
32°FSep 14Sep 19Sep 23Sep 25Sep 28Oct 1Oct 3Oct 7Oct 11
28°FSep 26Sep 30Oct 2Oct 5Oct 8Oct 11Oct 14Oct 18Oct 23
24°FOct 2Oct 6Oct 10Oct 14Oct 18Oct 22Oct 25Oct 29Nov 3
20°FOct 7Oct 14Oct 20Oct 24Oct 28Nov 1Nov 3Nov 7Nov 13
16°FOct 16Oct 24Oct 29Nov 1Nov 4Nov 8Nov 12Nov 17Nov 23

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°F1321261221171121081049890
32°F157150146142138134130125117
28°F181174170165161158154149142
24°F206199192187183178173167161
20°F226218212206202197191185177
16°F245236229224218213207200190

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
7,528
Cooling degree days, base 65°F
334
Growing degree days, base 40°F
3,847
Growing degree days, base 45°F
2,804
Growing degree days, base 50°F
1,938
Growing degree days, base 55°F
1,244
Growing degree days, base 60°F
710

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,21801
February1,07102
March93808
April663030
May4025140
June17927306
July37143572
August61125530
September24832268
October605269
November918012
December1,18900

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 9.8 km from Ulm. 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 USC00243753 (Great Falls WFO). Public domain.