When Will the First Frost Happen in St. Cloud This Fall?

Frost develops when the temperature is cold enough for water molecules in the air to freeze. The process is called Deposition (it’s the opposite of evaporation). Ice crystals appear without liquid water ever forming. This happens most frequently on surfaces that are wet and get cold much faster than the air around it like grassy fields, rooftops, or your favorite frost-sensitive plants.

Frost mainly forms on nights that are clear and cold with calm wind. Looking at the forecast for this week we will have plenty of clear and calm, but we are missing the cold as overnight lows stay in the 50s, and upper 40s.

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According to The Old Farmers Almanac, the classification of freeze temperatures is based on their effect on plants:

• Light freeze: 29° to 32°F (-1.7° to 0°C)—tender plants are killed.
• Moderate freeze: 25° to 28°F (-3.9° to -2.2°C)—widely destructive to most vegetation.
• Severe freeze: 24°F (-4.4°C) and colder—heavy damage to most garden plants.

The Old Farmers Almanac also uses data from NOAA to predict when the first and last frost of the season happens in St. Cloud. This year, the first frost of fall is predicted to happen on September 25th.

Last year the frost was really late, so it's hard to tell when exactly it will happen. But we know one thing for certain, the cold will come. It is Minnesota after all.