Warm storm triggers quick flooding in northeast US, southeast Canada
A warm storm brought rain over areas of deep snow and frozen rivers raising the risk of urban and ice jam flooding in the northern tier of the United States and the southern tier of Canada this week.
AccuWeather River Expert Alex Sosnowski discusses the Northeast flood threat.
A storm tracking well to the north pulled warm air along with it, raising the risk of flooding from rapidly melting snow near the United States and Canada borders through early Thursday morning, AccuWeather meteorologists warn. There is the likelihood of ice jam flooding, urban flooding and quick rises on some open streams and rivers in the region.
Recent mild weather has reduced or wiped out snow cover and ice on rivers in some areas of the Midwest and Northeast in the past week. Deep snow or ice remains on some rivers from Wisconsin and northern Michigan to upstate New York, northern New England and the southern tier of Ontario and Quebec. It's these locations that will be most prone to flooding from the same storm that triggered a severe weather outbreak farther south in the U.S. this week.
In some cases, such as in the Upper Midwest and the southern tier of Canada, heavy rain compensated for lower temperatures in the 30s to lower 40s F. In areas a bit farther to the east, in upstate New York and northern New England, only a light to moderate amount of rain will fall through early Thursday morning, but temperatures surged well into the 40s, 50s, and perhaps even near 60 with humid air accelerated the melting of the snow cover.
"One zone we are watching closely is from northern Wisconsin to northern Michigan for significant stream and river flooding," AccuWeather Meteorologist Brandon Buckingham said.
Sault Ste. Marie and Marquette, Michigan, as well as Rhinelander, Wisconsin, are among the towns in the northern U.S. at risk for significant flooding.
Ongoing rain and snow on the ground or where large piles of snow block storm drains can lead to urban flooding, with potentially deep enough water on some streets and highways to stall vehicles and block traffic. Canadian major metro areas such as Ottawa, Montreal, Quebec City and Toronto are likely to experience urban flooding problems from the thaw and storm.
"The greatest concern is where there is enough runoff into area streams and rivers that are frozen to lead to ice jam flooding," AccuWeather Senior Meteorologist Joe Lundberg said.
While the flooding cycle may not be as rapid and severe as some flooding events in the past, there may be flooding along unprotected areas of rivers that can last for days after the storm has departed. Some roads and bridges may be blocked by high water.
A sweep of cold air in the wake of the storm will follow from west to east during the latter part of this week and into the weekend. The cold air and freeze will slow and stop the runoff, but it will take a while for the rivers to respond. Large puddles, flooded areas and dampness on area roads will freeze.
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