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WHAT IS SNOWMELT FLOODING

From NWS Training Portal: flooding_factsheet.pdf (weather.gov)

A flood is considered a snowmelt flood when melting snow is a major source of the water involved. Unlike rainfall, which reaches the soil almost immediately, snow stores the water for some time until it melts, delaying the arrival of water downstream for days, weeks, or even months.

Once it does reach the soil, the water either soaks into the ground or runs off. If more water runs off than soaks in, flooding occurs.

How common are snowmelt floods? Are they severe? Snowmelt flooding typically occurs every year in the northern United States, with most snowmelt events being minor and localized. Eight of the most significant floods of the 20th century (in terms of area affected, property damage, and deaths) were related to snowmelt.

What causes snowmelt flooding? High soil moisture conditions prior to snowmelt, frozen ground, heavy snow cover, widespread heavy rain during the melt period, and rapid snowmelt (unseasonably warm temperatures, high humidity, rainfall, etc.)