Mid-December 2007 North American Winter Storms - Meteorological Synopsis

Meteorological Synopsis

Much of the affected areas were already hit by a significant winter storm during the weekend of December 1 and December 2. Many areas had received close to three-quarters of an inch of ice from Nebraska to Illinois, causing tens of thousands of power outages and at least 16 deaths across nine states and the Canadian province of Quebec, the latter receiving a major snow storm.

Following that winter storm, a large dome of cold air penetrated the Midwest following an Alberta Clipper, which was responsible for major flooding across the Pacific Northwest and moderate snows from Alberta to Maryland. The first wave of low pressure, which developed across the Southwest on December 8, produced light freezing rain throughout much of the Midwest and southern Ontario on December 9. A second stronger storm developed across the southwest on December 10 and gave significant snows to the higher elevations of Arizona near Flagstaff as well as in Colorado.

The storm then proceeded to produce a significant swath of ice across much of the Central Plains. Both storms in total produced between a half-inch to an inch of ice from Oklahoma to Wisconsin, while 8 to 24 inches of snow (20–60 cm) fell over the mountains of Utah, the highest amount being reported in northern Park City; 6 to 12 inches(15–30 cm) fell over Colorado and New Mexico while generally less than 6 inches fell on the northern side of the system from Nebraska to Quebec, although 10 inches (25 cm) fell in the Saguenay region of Quebec due to the orographic effect and Lake Saint-Jean. A mixture of snow, sleet, ice, and rain also fell across many of the affected areas. The main energy of the system responsible for the ice storm later moved east and affected portions of the Northeast and Middle Atlantic States with snow and rain on December 13, with the heaviest snow falling across southern and central New York and central New England. Portions of Massachusetts, Connecticut and New York received as much as 12 inches (30 cm) of snow from the storm, including 7 inches (18 cm) in Boston.

Another major winter storm developed on December 14 east of the Rockies and across the southern states and traveled across many of the same areas, bringing significant snows to areas that were affected by both ice storms. Portions of Kansas received over a foot (30 cm) of snow on top of the accumulated ice. The system moved across the Great Lakes region on December 15 and 16 and intensified while adding moisture from a developing coastal low as well as residual moisture from what was Tropical Storm Olga that affected most of the Antilles and Caribbean. Several areas in the Midwest and eastern North America received close to a foot of snow including Chicago, some areas of the Toronto and Detroit areas, Montreal, and Ottawa. Accumulations of as much as 20 inches (50 cm) fell across northern New England, northern New York, eastern Ontario from rural eastern Ottawa to Cornwall, and north of the Saint Lawrence River in the province of Quebec into the Charlevoix region. Thundersnow was even reported across portions of southern Ontario and Quebec. Widespread amounts of snow between 8 to 14 inches (20–35 cm) were reported across Ontario, Quebec, most of New England and the Canadian Maritimes as well as in several areas of the Midwest including Kansas and Missouri, while between a half-inch to an inch (13–25 mm) of ice fell across higher elevations in Maryland and Virginia with significant icing as well over West Virginia and Pennsylvania. This was accompanied by heavy rain between 2 to 4 inches (50–100 mm) south of the Mason-Dixon Line towards the Carolinas and the Southeast, with significant rainfall across the Middle Atlantic Coast, coastal sections of Nova Scotia, and the Avalon Peninsula of Newfoundland and Labrador. Additionally, heavy thunderstorms developed across the Southern states near the Gulf of Mexico coast, where tornado watches were issued for portions of Alabama, Florida, Georgia, and South Carolina on December 15 with several tornadoes later confirmed. The storm finally exited off the coast into the Atlantic Ocean on December 18.

The series of storms that affected the Midwest and East are similar to those that took place during January 2007 as several storms traveled across the same areas, killing at least 85 across several states and Canadian provinces. It was also similar to (but much less severe than) the historic Ice Storm of 1998 which blanketed much of eastern Canada from Ontario to New Brunswick.