A significant storm system is forecasted to move from the south-central United States to southeastern Canada in the early days of March, bringing heavy rain and rising temperatures. Meteorologists at AccuWeather are warning of potential major flooding as the thaw sets in, exacerbated by rapid snowmelt in regions hit by recent winter storms.
The presence of a deep snowpack in spring always carries the risk of swift melting that can lead to flooding. While such occurrences are uncommon in the high elevations of the West, they pose a more significant threat in lower elevations, particularly in the humid East where storms can draw moisture from the Gulf and Atlantic.
The areas from northern New England through upstate New York to southern Quebec and Ontario are at risk of sudden snowmelt and resultant flooding. A scenario of fast snowmelt combined with rainy weather is anticipated during the middle of the upcoming week.
Following a storm that will primarily affect Canada and northern New England over the weekend, cold air will help maintain much of the existing snow cover into the following week. The weekend storm is expected to deposit 3-6 inches of fresh snow, with higher amounts in some areas.
As the large storm approaches the central Great Lakes and southeastern Canada from Tuesday to Wednesday, it will draw moisture from the Gulf and Atlantic, bringing heavy rain and warmer temperatures. This quick shift to warmer weather, with temperatures soaring into the 30s, 40s, and even 50s Fahrenheit, will elevate the snowpack’s temperature, particularly where it nears the freezing point, leading to rapid melting.
Snow cover in central and northern New York, northern New England, southern Quebec, and southeastern Ontario is substantial, ranging from 1 to 3 feet, with pockets of even greater depth. Some areas are holding 5 to 10 inches of water within the snowpack.
With the potential for 1-2 inches of rain from the upcoming storm, combined with melting snow, a significant amount of water will be released, accelerating runoff into streams and rivers, potentially causing major flooding.
Urban areas with piled-up snow blocking drainage may face urban flooding, including Montreal, Quebec City, Toronto, and Ottawa in Canada, and Burlington, Plattsburgh, and Caribou in the United States.
AccuWeather advises staying informed about the situation through the free AccuWeather app, which provides real-time alerts. Urban flooding may occur across New England, the mid-Atlantic, the central Appalachians, and the Great Lakes region, impacting major cities like Boston, New York City, Philadelphia, Washington, D.C., and Pittsburgh.
In the northeastern United States, runoff resulting from one inch of rainfall can cause a moderate increase in the levels of small streams. Moving further southwest, there is a growing concern that parts of Kentucky, Tennessee, Ohio, Indiana, and West Virginia may experience heavy rainfall leading to potential flooding. This comes as many waterways are still elevated following a fatal downpour in mid-February.
Travelers are advised to brace for delays escalating between Tuesday and Wednesday with the onset of rain and the formation of fog in various areas. The risk of river flooding, particularly along secondary rivers in the St. Lawrence Valley, could persist for several days to a week before subsiding.
Certain factors may help limit the runoff from the storm, such as a more southerly trajectory which might restrict the melting of the critical deep snowpack. Additionally, lighter or intermittent rainfall could assist in reducing the risk of flooding. Furthermore, a scenario where cold air lingers throughout the storm could delay the warming of the snowpack, prolonging the duration of lower temperatures.
Looking ahead, more storms are expected with episodes of heavy rain as March progresses, possibly leading to recurring challenges with rising stream and river levels in the weeks to come.
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