interventions: Phenomenon
For snow to fall, moisture must be present in the atmosphere. Snow forms when the atmospheric temperature is at or below freezing (0°C or 32°F). If the ground temperature is at or below freezing, the snow will reach the ground. However, the snow can still reach the ground when the ground temperature is above freezing if the conditions are just right. In this case, snowflakes will begin to melt as they reach this higher temperature layer; the melting creates evaporative cooling, which cools the air immediately around the snowflake. This cooling slows down melting. As a general rule, though, snow will not form if the ground temperature is at least 5°C (41°F).
While it can be too warm to snow, it cannot be too cold to snow. Snow can occur even at incredibly low temperatures, as long as there is some source of moisture and some way to lift or cool the air. It is true, however, that most heavy snowfalls occur when there is relatively warm air near the ground—typically -9°C (15°F) or warmer—since warmer air can hold more water vapor.
Because snow formation requires moisture, very cold but very dry areas may rarely receive snow. Antarctica's Dry Valleys, for instance, form the largest ice-free portion of the continent. The Dry Valleys are quite cold but have very low humidity, and strong winds help wick any remaining moisture from the air. As a result, this extremely cold region receives little snow.
unsanctioned intervention: Palermo, Italy, 2023
materials: photomontage, gesso, acrylic paint, ink on rust colored rice paper (18 x 24 inches)
