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🍂 First Frost Dates for Helena, Montana 59625

The first 36°F frost date is 30% likely to be on Sep 10. (See detailed probabilities below.)

The first 32°F light freeze date is 30% likely to be on Sep 20. (See detailed probabilities below.)

(See also 🌷 Last Spring Frost Dates.)

First frost date probabilities for Helena, MT are based on historical climate data.

Always check your local forecast for the most up-to-date frost warnings.

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What is a First Frost Date?

The first fall frost signals the end of your local growing season. This date serves as an important deadline for gardeners and farmers. You'll need to complete harvesting before this point. Annuals and other tender plants will die back when frost hits, and perennial plants will enter their dormant phase for winter. Meanwhile, it's time to enjoy a cup of hot cocoa and a cozy sweater—and start planning your spring garden!

How to use the First Frost Date?

Watch your local weather forecasts in early fall to predict the first frost date. Harvest tender crops and protect vulnerable plants before frost arrives. For late-summer plantings, count backward from your area's average first frost date. This ensures your crops have enough time to mature. Keep track of when frost actually occurs in your garden each year. This helps you identify protected spots where the growing season might last longer.

First Frost Date Probabilities

Probability of frost (36°F) on or before...
10% chanceSep 2
20% chanceSep 7
30% chanceSep 10
40% chanceSep 13
50% chanceSep 15
60% chanceSep 17
70% chanceSep 20
80% chanceSep 23
90% chanceSep 27
Probability of light freeze (32°F) on or before...
10% chanceSep 12
20% chanceSep 17
30% chanceSep 20
40% chanceSep 23
50% chanceSep 25
60% chanceSep 27
70% chanceSep 30
80% chanceOct 3
90% chanceOct 7
Probability of moderate freeze (28°F) on or before...
10% chanceSep 23
20% chanceSep 27
30% chanceSep 30
40% chanceOct 2
50% chanceOct 5
60% chanceOct 7
70% chanceOct 10
80% chanceOct 13
90% chanceOct 17
Probability of moderate hard freeze (24°F) on or before...
10% chanceSep 30
20% chanceOct 4
30% chanceOct 8
40% chanceOct 12
50% chanceOct 15
60% chanceOct 17
70% chanceOct 20
80% chanceOct 24
90% chanceOct 28
Probability of hard freeze (20°F) on or before...
10% chanceOct 8
20% chanceOct 15
30% chanceOct 19
40% chanceOct 23
50% chanceOct 26
60% chanceOct 28
70% chanceOct 31
80% chanceNov 4
90% chanceNov 10
Probability of severe hard freeze (16°F) on or before...
10% chanceOct 19
20% chanceOct 25
30% chanceOct 30
40% chanceNov 1
50% chanceNov 5
60% chanceNov 8
70% chanceNov 12
80% chanceNov 16
90% chanceNov 22

Agricultural climatic data from weather station: HELENA RGNL AP (USW00024144)

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