After forming off the coast of Southern California and bringing much needed rain to the Desert Southwest, the first major winter storm of the season is dumping heavy snow in the southern Rockies and will move across the Northern Plains today. Icy conditions will prevail in western Kansas, southern Nebraska and northern Missouri, with significant snowfall to the north of that swath. Southward, steady rains will drench the Central Plains and lower Midwest.
Tomorrow, the storm will move across the Great Lakes and into the Northeast, bringing a mix of ice and snow to that region. Finally, gaining strength off the New England Coast, it is forecast to dump heavy snow on the Northern Appalachians.
Contrary to popular perception, such storms are not a massive swirl of moisture that drains itself as it moves across the country. Rather, the storm is a low pressure center (and its associated cold front) that pulls in moisture from the south and forces it to collide with or override cold air to the north; depending upon the depth and temperature of the cold air, the precipitation falls as rain, freezing rain, sleet or snow. If the storm encounters air that is deficient in moisture, precipitation will be limited or not occur at all.
