Now that the spring season is here, residents across the United States should be aware of any potential flooding hazards that could arise. Depending on where you are in the country, flooding hazards can take different forms. In the case of the Northern Tier and mountainous areas, snowmelt flooding can likely occur.

Snowmelt flooding occurs when the major source of water involved in a flooding hazard is caused by melting snow. While rainfall can reach the soil almost immediately, a snowpack can delay the arrival of water to the soil for days, weeks, or even months. This depends on how quickly the temperatures reach above freezing, which causes the snowpack to melt. Once it begins to melt and does reach the soil, water from snowmelt behaves much as it would if it had come from rain instead of snow. The water can either infiltrate into the soil, run off, or both. When there is more water than what the soil can absorb, flooding occurs.

Forecasters should keep an eye out for how much snow is on the ground and how cold conditions have been prior to a potential flooding event. The colder it is, the more likely deep, hard ground frost can develop and prevent snowmelt from infiltrating into the soil. The more snow there is on the ground, the more stored water there is available for snowmelt. Widespread snow can also delay spring warming and keep air temperatures lower, which also increases the potential for more snowmelt. Rain falling while snow is still on the ground can also help to melt the snowpack. Each scenario mentioned can lead to flooding hazards by snowmelt.

Flooding by snowmelt is usually a slow phenomenon. Snowmelt rates are typically comparable to light or moderate rainfall events, but can be faster during unusually warm periods with high dew points.