Anatomy of an Eastern Snowstorm

This morning, a massive snowstorm is developing over the Eastern U.S., fueled by several atmospheric and geographic factors.  A potent area of low pressure, currently over western Alabama, is sweeping Gulf of Mexico moisture across the Southeast.  In concert, a high pressure dome over the Great Lakes region is funneling cold air down from Canada, spreading sub-freezing air across all but the southernmost States.

The clash zone between the warm, moist southerly flow and the cold, dry air to the north is currently producing snow across the Ohio and Tennessee Valleys; along the southern edge of this band, an ice storm (including sleet and freezing rain) is expected to develop.  Later today, as the low pressure moves to the Eastern Seaboard, energized by the subtropical jet stream, it will intensify, pulling in copious moisture from the Atlantic Ocean.

Rather than moving rapidly up the coast, the storm is forecast to creep northward, stalled by the high pressure dome to the north.  This "blocking high," combined with the potent low, is expected to produce a long-lasting blizzard in the Mid-Atlantic region, perhaps dropping more than two feet of snow (especially along the eastern flank of the Appalachians).  Major cities and their airports will likely shut down, affecting at least 45 million people in this heavily populated region of the country.

Update:  As of 1-23-16, the storm has spread farther north than initially expected, now affecting at least 85 million people.  Power outages and coastal flooding (especially in New Jersey and southern New York) have become major problems.  Forty inches of snow have fallen in some areas of Virginia.