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The depth of low-level warm air (below the freezing level) needed to melt snow falling from above to rain varies from about 230–460 m (750–1,500 ft) and depends on the mass of the flakes and the lapse rate of the melting layer. Rain and snow typically mix when the melting layer depth falls between these values as rain starts forming when in ...
Freezing rain develops when falling snow encounters a layer of warm air aloft, typically around the 800 mbar (800 hPa; 80 kPa) level, causing the snow to melt and become rain. As the rain continues to fall, it passes through a layer of subfreezing air just above the surface and cools to a temperature below freezing (0 °C or 32 °F or 273 K).
The snow melts into rain then refreezes just as it hits the cold ground. Since the rain is not freezing until it reaches the surface, it still falls like regular rain and therefore looks and feels ...
As snow in Minnesota, North Dakota, and South Dakota begins to melt and flow into the Red River, the presence of downstream ice can act as a dam and force upstream water to rise. Colder temperatures downstream can also potentially lead to freezing of water as it flows north, thus augmenting the ice dam problem.
"The risk of flooding may also extend into portions of the Ohio Valley, central Appalachians and the Mid-Atlantic, where rain combines with melting snow and ice jams on area streams and rivers ...
Unfortunately, there is the potential for rapidly melting snow combined with rain during the middle of this week. Cold air will remain entrenched over Canada and northern New England early this week.
Ice dams on roofs form when accumulated snow on a sloping roof melts and flows down the roof, under the insulating blanket of snow, until it reaches below freezing temperature air, typically at the eaves. When the meltwater reaches the freezing air, ice accumulates, forming a dam, and snow that melts later cannot drain properly through the dam ...
In some cases, the rain may melt all the snow that falls in southern Minnesota, he added. But in the Twin Cities, he expects at least 2 to 4 inches will remain on the ground by the morning.