According to catastrophe modeling firm AIR Worldwide, a disturbance tracking across the Great Lakes is expected to merge later tonight with another low pressure system developing off the Mid-Atlantic Coast. The combined system is forecast to pass to the south of Cape Cod and then intensify rapidly. By Friday evening, heavy snow is expected to fall across southern New England, and by Saturday morning winds are expected to be very intense for coastal New England.
“Convective (thunderstorm) activity embedded within the system could result in short periods of intense snowfall, with rates reaching up to three to five inches per hour,” said Dr. Tim Doggett, senior principal scientist at AIR Worldwide. “The heaviest snow is expected from Friday evening through Saturday morning. This storm has the potential to impact a significant swath of the Northeast, depending on where the rain/snow line falls. For this reason, the National Weather Service has issued blizzard watches for locations from Long Island to southern New Hampshire border and for points as far west as Hartford, Conn.”
“Uncertainty still surrounds the exact track this winter storm will take. A shift 50 miles north or south will make a notable difference in snow totals and wind intensities impacting the coast. What is certain is that there is a high probability of snow accumulations of more than one foot over much of southern New England and parts of New York during the next 48 hours or so. A little more than 35 years ago, the Blizzard of ’78 hit Massachusetts and Rhode Island on February 5-7, a storm of historic proportions that still resonates for those who lived through the experience.”
According to AIR, the combination of heavy snow and intense winds means that drifting snow will be a problem over the watch area, increasing the possibility of roof collapse for light metal structures with large roof areas. Design snow loads for structures vary across the United States. As little as zero pounds per square foot is allowed in Florida, southern Louisiana, Texas, and parts of the Southwest, while as much as 100 pounds per square foot is required in Michigan’s Upper Peninsula and northernmost Maine. Ten to 20 inches of snow can produce loads of roughly 15 to 30 pounds per square foot on flat roofs. Other building elements—porches, carports, awnings, and gutters—which often do not receive any specific design attention, are similarly vulnerable under the forecast conditions.
Dr. Doggett noted, “Further complicating the scenario is the possibility that rain and sleet may fall as mixed precipitation in southeast Massachusetts and Rhode Island. If this happens, then there will be more weight added to the snow, and the damage potential will increase. The accumulated snow, together with winds, may also cause downed trees across the region, causing damage to structures and automobiles. They may also bring down power lines, causing power outages. In areas with long duration outages, lack of heat may cause pipe freeze issues as well. In addition, the possibility of greater damage to structures compromised by Sandy and not yet repaired increases over the forecast area.”