ESS124
Prof.
Jin-Yi Yu
Flooding Compounded by
Snowmelt
Ice jam on the Red lake River at Grand Forks,
North Dakota, during a
flood in 1997.
•Many damaging widespread floods in the northern US occur when the rapid melting
of a winter
snowpack enhances runoff from heavy spring rains.
•Heavy rain and rapid snowmelt often occur together when a subtropical moist airmass moves over a snow-covered region during
the late
winter or early spring.
•The ground is often frozen beneath the snow, preventing infiltration and enhancing
runoff.
•The situation is often made worst by ice jams on rivers that have accumulated
significant ice cover
over the proceeding weeks or months.