Usually,this requires near-freezing temperatures, light winds and changing conditions in Earth's atmosphere.

VOA: special.2011.01.11

Below freezing temperatures combined with compacting snow has meant traffic chaos for drivers in Germany, Poland and elsewhere.

VOA: standard.2009.12.21

In climates where temperatures fall below freezing, plant mums at least six weeks before the first frost is expected.

VOA: special.2010.06.29